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A systematic study is conducted to compare the performances and stability of active layers employing a high performance electron donor (PBDB‐T) combined with state‐of‐the‐art fullerene (PC71BM), nonfullerene (ITIC), and polymer (N2200) electron acceptors. The impact of the chemical nature of the acceptor on the durability of organic solar cells (OSCs) is elucidated by monitoring their photovoltaic performances under light exposure or dark conditions in the presence of oxygen. PC71BM molecules exhibit a higher resistance toward oxidation compared to nonfullerene acceptors. Unencapsulated PBDB‐T:PC71BM OSCs display relatively stable performances at room temperature when stored in air for 3 months. However, when exposed to temperatures above 80 °C, their active materials demix causing notable reductions in the short‐circuit densities. Such detrimental demixing can also be seen for PBDB‐T:ITIC active layers above 120 °C. Although N2200 chains irreversibly degrade when exposed to air, thermally induced demixing does not occur in PBDB‐T:N2200 active layers annealed up to 200 °C. In summary, fullerene OSCs may be the best currently available choice for unencapsulated room temperature applications but if oxidation of the polymer acceptors can be avoided, all polymer active layers should enable the fabrication of highly durable OSCs with lifetimes matching the requirements for OSC commercialization.
Varun Vohra; Yumi Matsunaga; Tomoaki Takada; Ayumu Kiyokawa; Luisa Barba; William Porzio. Impact of the Electron Acceptor Nature on the Durability and Nanomorphological Stability of Bulk Heterojunction Active Layers for Organic Solar Cells. Small 2020, 17, e2004168 .
AMA StyleVarun Vohra, Yumi Matsunaga, Tomoaki Takada, Ayumu Kiyokawa, Luisa Barba, William Porzio. Impact of the Electron Acceptor Nature on the Durability and Nanomorphological Stability of Bulk Heterojunction Active Layers for Organic Solar Cells. Small. 2020; 17 (2):e2004168.
Chicago/Turabian StyleVarun Vohra; Yumi Matsunaga; Tomoaki Takada; Ayumu Kiyokawa; Luisa Barba; William Porzio. 2020. "Impact of the Electron Acceptor Nature on the Durability and Nanomorphological Stability of Bulk Heterojunction Active Layers for Organic Solar Cells." Small 17, no. 2: e2004168.
Using ultrafast spectroscopy, we investigate the photophysics of water-processable nanoparticles composed of a block copolymer electron donor and a fullerene derivative electron acceptor.
Lucia Ganzer; Stefania Zappia; Mattia Russo; Anna Maria Ferretti; Varun Vohra; Marianna Diterlizzi; Maria Rosa Antognazza; Silvia Destri; Tersilla Virgili. Ultrafast spectroscopy on water-processable PCBM: rod–coil block copolymer nanoparticles. Physical Chemistry Chemical Physics 2020, 22, 26583 -26591.
AMA StyleLucia Ganzer, Stefania Zappia, Mattia Russo, Anna Maria Ferretti, Varun Vohra, Marianna Diterlizzi, Maria Rosa Antognazza, Silvia Destri, Tersilla Virgili. Ultrafast spectroscopy on water-processable PCBM: rod–coil block copolymer nanoparticles. Physical Chemistry Chemical Physics. 2020; 22 (45):26583-26591.
Chicago/Turabian StyleLucia Ganzer; Stefania Zappia; Mattia Russo; Anna Maria Ferretti; Varun Vohra; Marianna Diterlizzi; Maria Rosa Antognazza; Silvia Destri; Tersilla Virgili. 2020. "Ultrafast spectroscopy on water-processable PCBM: rod–coil block copolymer nanoparticles." Physical Chemistry Chemical Physics 22, no. 45: 26583-26591.
Rubbing the donor in bilayer organic solar cells promotes the formation of adequate concentration gradients in the active layers. The improved charge collection yields large enhancements in the performances of fullerene and non-fullerene solar cells.
Mohd Zaidan Abdul Aziz; Koichi Higashimine; Nobutaka Shioya; Takafumi Shimoaka; Takeshi Hasegawa; Heisuke Sakai; Varun Vohra; Hideyuki Murata. Controlling the concentration gradient in sequentially deposited bilayer organic solar cells via rubbing and annealing. RSC Advances 2020, 10, 37529 -37537.
AMA StyleMohd Zaidan Abdul Aziz, Koichi Higashimine, Nobutaka Shioya, Takafumi Shimoaka, Takeshi Hasegawa, Heisuke Sakai, Varun Vohra, Hideyuki Murata. Controlling the concentration gradient in sequentially deposited bilayer organic solar cells via rubbing and annealing. RSC Advances. 2020; 10 (61):37529-37537.
Chicago/Turabian StyleMohd Zaidan Abdul Aziz; Koichi Higashimine; Nobutaka Shioya; Takafumi Shimoaka; Takeshi Hasegawa; Heisuke Sakai; Varun Vohra; Hideyuki Murata. 2020. "Controlling the concentration gradient in sequentially deposited bilayer organic solar cells via rubbing and annealing." RSC Advances 10, no. 61: 37529-37537.
The integration of noble metals nanostructures can be an effective method to improve the performance of organic solar cells by scattering the incident light that reaches the active layer. The resulting elongated active optical trail span of the incident photons can enhance the amount of absorbed photons in the active layer. Herein, this article reviews studies on the incorporation of noble metals and metal oxides nanostructures into bulk heterojunction polymer solar cells (BHJ PSCs) device architectures. In particular, we focus on presenting the latest progress in PCSs employing various fullerene electron acceptors with an emphasis on their performances, optical and structural properties upon integration of the mentioned nanostructure. We discuss the effect of metallic nanoparticles (NPs) integration, such as gold (Au) and silver (Ag), on the performance of PSCs according to theoretical interpretation. In addition to the metallic NPs, we discuss the influence of metal oxide nanoparticle incorporation, such as CuO, ZnO and TiO2, on the performance of the organic based solar cells.
Popoti J. Maake; Amogelang S. Bolokang; Christopher J. Arendse; Varun Vohra; Emmanuel I. Iwuoha; David E. Motaung. Metal oxides and noble metals application in organic solar cells. Solar Energy 2020, 207, 347 -366.
AMA StylePopoti J. Maake, Amogelang S. Bolokang, Christopher J. Arendse, Varun Vohra, Emmanuel I. Iwuoha, David E. Motaung. Metal oxides and noble metals application in organic solar cells. Solar Energy. 2020; 207 ():347-366.
Chicago/Turabian StylePopoti J. Maake; Amogelang S. Bolokang; Christopher J. Arendse; Varun Vohra; Emmanuel I. Iwuoha; David E. Motaung. 2020. "Metal oxides and noble metals application in organic solar cells." Solar Energy 207, no. : 347-366.
Conjugated polyelectrolytes are commonly employed as interlayers to modify organic solar cell (OSC) electrode work functions but their use as an electron donor in water-processed OSC active layers has barely been investigated. Here, we demonstrate that poly[3-(6’-N,N,N-trimethyl ammonium)-hexylthiophene] bromide (P3HTN) can be employed as an electron donor combined with a water-soluble fullerene (PEG-C60) into eco-friendly active layers deposited from aqueous solutions. Spin-coating a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layer prior to the P3HTN:PEG-C60 active layer deposition considerably increases the open-circuit voltage (Voc) of the OSCs to values above 1.3 V. Along with this enhanced Voc, the OSCs fabricated with the PEDOT:PSS interlayers exhibit 10-fold and 5-fold increases in short-circuit current density (Jsc) with respect to those employing bare indium tin oxide (ITO) and molybdenum trioxide coated ITO anodes, respectively. These findings suggest that the enhanced Jsc and Voc in the water-processed OSCs using the PEDOT:PSS interlayer cannot be solely ascribed to a better hole collection but rather to ion exchanges taking place between PEDOT:PSS and P3HTN. We investigate the optoelectronic properties of the newly formed polyelectrolytes using absorption and photoelectron spectroscopy combined with hole transport measurements to elucidate the enhanced photovoltaic parameters obtained in the OSCs prepared with PEDOT:PSS and P3HTN.
Varun Vohra; Shunsuke Shimizu; Yuko Takeoka. Water-Processed Organic Solar Cells with Open-Circuit Voltages Exceeding 1.3V. Coatings 2020, 10, 421 .
AMA StyleVarun Vohra, Shunsuke Shimizu, Yuko Takeoka. Water-Processed Organic Solar Cells with Open-Circuit Voltages Exceeding 1.3V. Coatings. 2020; 10 (4):421.
Chicago/Turabian StyleVarun Vohra; Shunsuke Shimizu; Yuko Takeoka. 2020. "Water-Processed Organic Solar Cells with Open-Circuit Voltages Exceeding 1.3V." Coatings 10, no. 4: 421.
Oxygen-barrier properties of PC71BM and MoO3 enable the production of long-lasting organic solar cells employing highly oxygen-sensitive small electron donors.
Takayuki Uchiyama; Takashi Sano; Yoshiko Okada-Shudo; Varun Vohra. Durable organic solar cells produced by in situ encapsulation of an air-sensitive natural organic semiconductor by the fullerene derivative and the metal oxide layer. Journal of Materials Chemistry C 2020, 8, 7162 -7169.
AMA StyleTakayuki Uchiyama, Takashi Sano, Yoshiko Okada-Shudo, Varun Vohra. Durable organic solar cells produced by in situ encapsulation of an air-sensitive natural organic semiconductor by the fullerene derivative and the metal oxide layer. Journal of Materials Chemistry C. 2020; 8 (21):7162-7169.
Chicago/Turabian StyleTakayuki Uchiyama; Takashi Sano; Yoshiko Okada-Shudo; Varun Vohra. 2020. "Durable organic solar cells produced by in situ encapsulation of an air-sensitive natural organic semiconductor by the fullerene derivative and the metal oxide layer." Journal of Materials Chemistry C 8, no. 21: 7162-7169.
Two terthiophene-isoindigo copolymers (P3TI-O and P3TI-D) were successfully designed and synthesized. Octyl(O) and dodecyl(D) alkyl side chains were appended at the third position of the first and fourth position of the last thiophene on the terthiophene donor units in P3TI-O and P3TI-D, respectively. The band gaps of these copolymers were less than 1.7 eV. We found intramolecular charge transfer states in both copolymers which were generated with time constants of 4.5 ps and 13 ps for the copolymers with short and long alkyl side chains on their donor units, respectively. These results indicate that an almost 3-fold faster intramolecular charge transfer process occurs when the alkyl side chain are shortened by four methyl units. Owing to a better interchain charge transfer, P3TI-O exhibits a more efficient exciton diffusion compared to P3TI-D, thus leading to longer exciton lifetimes in the copolymer with shorter alkyl side chains. Consequently, when blended with PC71BM in bulk heterojunctions, P3TI-O showed a better exciton dissociation efficiency compared to P3TI-D. These results correlate well with the higher short circuit current densities observed in P3TI-O:PC71BM inverted architecture organic solar cells compared to the P3TI-D:PC71BM ones .
Newayemedhin A. Tegegne; Zelalem Abdissa; Wendimagegn Mammo; Takayuki Uchiyama; Yoshiko Okada-Shudo; Francesco Galeotti; William Porzio; Mats R. Andersson; Derck Schlettwein; Varun Vohra; Heinrich Schwoerer. Effect of Alkyl Side Chain Length on Intra- and Intermolecular Interactions of Terthiophene–Isoindigo Copolymers. The Journal of Physical Chemistry C 2020, 124, 9644 -9655.
AMA StyleNewayemedhin A. Tegegne, Zelalem Abdissa, Wendimagegn Mammo, Takayuki Uchiyama, Yoshiko Okada-Shudo, Francesco Galeotti, William Porzio, Mats R. Andersson, Derck Schlettwein, Varun Vohra, Heinrich Schwoerer. Effect of Alkyl Side Chain Length on Intra- and Intermolecular Interactions of Terthiophene–Isoindigo Copolymers. The Journal of Physical Chemistry C. 2020; 124 (18):9644-9655.
Chicago/Turabian StyleNewayemedhin A. Tegegne; Zelalem Abdissa; Wendimagegn Mammo; Takayuki Uchiyama; Yoshiko Okada-Shudo; Francesco Galeotti; William Porzio; Mats R. Andersson; Derck Schlettwein; Varun Vohra; Heinrich Schwoerer. 2020. "Effect of Alkyl Side Chain Length on Intra- and Intermolecular Interactions of Terthiophene–Isoindigo Copolymers." The Journal of Physical Chemistry C 124, no. 18: 9644-9655.
Tomoaki Takada; Takayuki Uchiyama; Yoshiko Okada-Shudo; Katsuhito Hoshino; Ko Koizumi; Yuko Takeoka; Varun Vohra. High Performance Organic Solar Cells Fabricated Using Recycled Transparent Conductive Substrates. ACS Sustainable Chemistry & Engineering 2020, 8, 5807 -5814.
AMA StyleTomoaki Takada, Takayuki Uchiyama, Yoshiko Okada-Shudo, Katsuhito Hoshino, Ko Koizumi, Yuko Takeoka, Varun Vohra. High Performance Organic Solar Cells Fabricated Using Recycled Transparent Conductive Substrates. ACS Sustainable Chemistry & Engineering. 2020; 8 (14):5807-5814.
Chicago/Turabian StyleTomoaki Takada; Takayuki Uchiyama; Yoshiko Okada-Shudo; Katsuhito Hoshino; Ko Koizumi; Yuko Takeoka; Varun Vohra. 2020. "High Performance Organic Solar Cells Fabricated Using Recycled Transparent Conductive Substrates." ACS Sustainable Chemistry & Engineering 8, no. 14: 5807-5814.
Ternary blend active layers that include an additional electron donor or electron acceptor material provide the means to easily tune the transmission properties of semitransparent organic solar cells (OSCs) by simply changing the relative concentration of each active material. We added a non-fullerene acceptor (ITIC) into a well-studied donor:acceptor active layer (PCDTBT:PC71BM) that can be produced in air and demonstrates long term operational stability. We investigated the optoelectronic properties of the resulting OSCs and observed that partially replacing the fullerene electron acceptor, PC71BM, with ITIC produces uniformly absorbing active layers which, however, generate a slight decrease in photovoltaic performances compared to the reference binary OSCs. On the other hand, adding ITIC to an optimized PCDTBT:PC71BM ratio of 1:4 leads to a slight increase in short-circuit current density from these ternary OSCs with respect to the binary ones. In semitransparent OSCs fabricated with a PCDTBT:PC71BM:ITIC ratio of 1:4:1, power conversion efficiencies of 4%, average visible transparencies around 40% and color rendering indices of 97 are produced. As the addition of ITIC does not affect the long term operational stability of the unencapsulated PCDTBT:PC71BM OSCs, our study opens the path to the fabrication of stable semitransparent OSCs with balanced optoelectronic properties which could readily be applied as solar energy-harvesting photovoltaic windows.
Takashi Sano; Shusei Inaba; Varun Vohra. Ternary Active Layers for Neutral Color Semitransparent Organic Solar Cells with PCEs over 4%. ACS Applied Energy Materials 2019, 2, 2534 -2540.
AMA StyleTakashi Sano, Shusei Inaba, Varun Vohra. Ternary Active Layers for Neutral Color Semitransparent Organic Solar Cells with PCEs over 4%. ACS Applied Energy Materials. 2019; 2 (4):2534-2540.
Chicago/Turabian StyleTakashi Sano; Shusei Inaba; Varun Vohra. 2019. "Ternary Active Layers for Neutral Color Semitransparent Organic Solar Cells with PCEs over 4%." ACS Applied Energy Materials 2, no. 4: 2534-2540.
Push-coating is a simple process that can be employed for extremely low-cost polymer electronic device production. Here, we demonstrate its application to the fabrication of poly(2,7-carbazole-alt-dithienylbenzothiadiazole) (PCDTBT):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) active layers processed in air, yielding similar photovoltaic performances as thermally annealed spin-coated thin films when used in inverted polymer solar cells (PSCs). During push-coating, the polydimethylsiloxane (PDMS) layer temporarily traps the deposition solvent, resulting in a simultaneous film formation and solvent annealing effect. This removes the necessity for a post-deposition thermal annealing step which is required for spin-coated PSCs to produce high photovoltaic performances. Optimized PSC active layers are produced with a push-coating time of 5 min at room temperature with 20 times less hazardous solvent and 40 times less active material than spin-coating. Annealed spin-coated active layers and active layers push-coated for 5 min both produce average power conversion efficiencies (PCEs) of 5.77%, while those push-coated for a shorter time of 1 min yield a slightly lower value of 5.59%. We demonstrate that, despite differences in their donor:acceptor vertical concentration gradients, unencapsulated PCDTBT:PC71BM active layers push-coated for 1 min produce PSCs with similar operational stability and up-scaling capacity as thermally annealed spin-coated ones. As fast device fabrication can be achieved with short-time push-coating, we further demonstrate the potential of this deposition technique by manufacturing push-coated PSC-based semi-transparent photovoltaic devices with a PCE of 4.23%, relatively neutral colors and an average visible transparency of 40.2%. Our work thus confirms that push-coating is not limited to the widely employed poly(3-hexylthiophene-2,5-diyl) but can also be used with low bandgap copolymers and opens the path to low-cost and eco-friendly, yet efficient and stable PSCs.
Shusei Inaba; Ryosuke Arai; Geanina Valentina Mihai; Oana Lazar; Calin Moise; Marius Enachescu; Yuko Takeoka; Varun Vohra. Eco-Friendly Push-Coated Polymer Solar Cells with No Active Material Wastes Yield Power Conversion Efficiencies over 5.5%. ACS Applied Materials & Interfaces 2019, 11, 10785 -10793.
AMA StyleShusei Inaba, Ryosuke Arai, Geanina Valentina Mihai, Oana Lazar, Calin Moise, Marius Enachescu, Yuko Takeoka, Varun Vohra. Eco-Friendly Push-Coated Polymer Solar Cells with No Active Material Wastes Yield Power Conversion Efficiencies over 5.5%. ACS Applied Materials & Interfaces. 2019; 11 (11):10785-10793.
Chicago/Turabian StyleShusei Inaba; Ryosuke Arai; Geanina Valentina Mihai; Oana Lazar; Calin Moise; Marius Enachescu; Yuko Takeoka; Varun Vohra. 2019. "Eco-Friendly Push-Coated Polymer Solar Cells with No Active Material Wastes Yield Power Conversion Efficiencies over 5.5%." ACS Applied Materials & Interfaces 11, no. 11: 10785-10793.
β-carotene (bCar) is an abundant natural organic semiconductor that can be extracted from tomatoes or carrots at extremely low costs. Using natural bCar as electron donor combined with a C70 derivative (PC71BM) as electron acceptor in bulk heterojunction active layers, we successfully fabricated efficient inverted organic solar cells (OSCs) processed in air without encapsulation. Unlike conventional OSCs produced with synthetic materials, higher short-circuit current densities are achieved in ultrathin active layers (~30 nm) compared to thicker ones (~ 90 nm). This peculiar behavior can be ascribed to the limited hole transport properties of bCar that limits the charge collection efficiency in 90 nm-thick bCar:fullerene OSCs. Our results demonstrate that higher boiling point solvents induce crystalline transformation of bCar in thin active layers resulting in OSCs with fill factors around 35% and average power conversion efficiencies (PCEs) of 0.58%. These devices demonstrate stable operation under constant illumination and are the best performing bCar-based OSCs published to date. They exhibit a 4-fold increase in PCE compared to previously reported bCar:fullerene OSCs, thus opening the path to low-cost yet efficient bCar biophotovoltaic device fabrication.
Varun Vohra; Takayuki Uchiyama; Shusei Inaba; Yoshiko Okada-Shudo. Efficient Ultrathin Organic Solar Cells with Sustainable β-Carotene as Electron Donor. ACS Sustainable Chemistry & Engineering 2019, 7, 4376 -4381.
AMA StyleVarun Vohra, Takayuki Uchiyama, Shusei Inaba, Yoshiko Okada-Shudo. Efficient Ultrathin Organic Solar Cells with Sustainable β-Carotene as Electron Donor. ACS Sustainable Chemistry & Engineering. 2019; 7 (4):4376-4381.
Chicago/Turabian StyleVarun Vohra; Takayuki Uchiyama; Shusei Inaba; Yoshiko Okada-Shudo. 2019. "Efficient Ultrathin Organic Solar Cells with Sustainable β-Carotene as Electron Donor." ACS Sustainable Chemistry & Engineering 7, no. 4: 4376-4381.
Natural photosynthetic systems contain several dyes such as carotenoids or chlorophylls which are adequately arranged to produce efficient photoinduced charge separation and electron transfer. Several research groups have attempted integrating these natural dyes and photosynthetic systems into functional organic solar cells (OSCs) producing power conversion efficiencies (PCEs) up to 0.99%. The studies presented in this short review emphasize that functionalization of natural dyes can considerably improve their PCEs. For instance, chlorophyll derivatives can yield PCEs up to 2.1%, and copolymers produced with isoindigo as an electron-deficient unit generate high PCEs up to 8%, respectively, when combined with fullerene C70 based electron acceptors in the OSC active layers. An alternative approach for natural dye integration into OSC architectures is to place these light-harvesting antennas at the interface between the active layer and the charge collection layers in these low-cost photovoltaic devices. This strategy produces large PCE increases up to 35% with respect to OSCs prepared without the interlayer. When light-harvesting systems are combined with silver nanoprisms as interlayers, additional localized surface plasmon resonance effects result in high-performance OSCs that integrate natural photosynthetic systems and demonstrate a PCE over the milestone value of 10%.
Varun Vohra. Natural Dyes and Their Derivatives Integrated into Organic Solar Cells. Materials 2018, 11, 2579 .
AMA StyleVarun Vohra. Natural Dyes and Their Derivatives Integrated into Organic Solar Cells. Materials. 2018; 11 (12):2579.
Chicago/Turabian StyleVarun Vohra. 2018. "Natural Dyes and Their Derivatives Integrated into Organic Solar Cells." Materials 11, no. 12: 2579.
We fabricate self-assembled templates to produce textured polydimethylsiloxane (PDMS) with quasi-random dimension distributions which are employed as light manipulation coatings in polymer solar cells (PSCs). When deposited at the PSC glass/air interface, PDMS films with microdome-like structures enhance the short-circuit current density (Jsc) by 7.9% through combined anti-reflective and scattering effects. The PSC power conversion efficiency can thus be improved from 6.75% to 7.28% and a maximum Jsc increase of 21% is observed for incident light tilted by 30 degrees. We compare structures with different diameter dispersities and confirm that quasi-randomness in textured coatings can increase their light scattering ability. GRAPHICAL ABSTRACT IMPACT STATEMENT Unlike costly lithographic techniques, this self-assembled approach opens the path to low-cost fabrication of quasi-random microtextured coatings for PSCs to efficiently harvest sunlight throughout the day (at various incident angles).
Takahiro Takumi; Savanna Lloyd; Hideyuki Murata; Varun Vohra. Low-cost light manipulation coatings for polymer solar cell photocurrent increase under various incident angles. Materials Research Letters 2018, 7, 68 -74.
AMA StyleTakahiro Takumi, Savanna Lloyd, Hideyuki Murata, Varun Vohra. Low-cost light manipulation coatings for polymer solar cell photocurrent increase under various incident angles. Materials Research Letters. 2018; 7 (2):68-74.
Chicago/Turabian StyleTakahiro Takumi; Savanna Lloyd; Hideyuki Murata; Varun Vohra. 2018. "Low-cost light manipulation coatings for polymer solar cell photocurrent increase under various incident angles." Materials Research Letters 7, no. 2: 68-74.
Sunlight is among the most abundant energy sources available on our planet. Finding adequate solutions to properly and efficiently harvest it is of major importance to potentially solve the global energy crisis. Polymer solar cells have been introduced in the late 20th century as low‐cost and easily processed alternative to the state‐of‐the‐art silicon photovoltaics. Their power conversion efficiencies, which were initially rather low, are constantly improving and now reach values close to 15 %. As their optical properties can be easily tuned, designing active layer which absorb homogeneously throughout the visible spectrum is relatively simple. These peculiar characteristics enable the possibility to fabricate visibly transparent solar cells with high color rendering indices which can be employed as photovoltaic windows. After reviewing some of the most successful examples of polymer solar cell‐based transparent photovoltaic window fabrication, I will discuss the possibility to produce these devices in a sustainable and/or eco‐friendly manner while maintaining their performances.
Varun Vohra. Can Polymer Solar Cells Open the Path to Sustainable and Efficient Photovoltaic Windows Fabrication? The Chemical Record 2018, 19, 1166 -1178.
AMA StyleVarun Vohra. Can Polymer Solar Cells Open the Path to Sustainable and Efficient Photovoltaic Windows Fabrication? The Chemical Record. 2018; 19 (7):1166-1178.
Chicago/Turabian StyleVarun Vohra. 2018. "Can Polymer Solar Cells Open the Path to Sustainable and Efficient Photovoltaic Windows Fabrication?" The Chemical Record 19, no. 7: 1166-1178.
Push-coating is a green and extremely low-cost process in which only few microliters of conjugated polymer solutions are used to produce thin films using capillary forces. Here, we adapt this fabrication technique to replicate self-assembled nanoporous structures on green and red light-emitting conjugated polymer thin films. These films display ring-like photoluminescence and are successfully integrated into polymer light-emitting devices as emitting layers. At low applied voltages, the green-emitting devices exhibit electroluminescence from hexagonally arranged nanopixel arrays resulting from a stronger electric field in the thinner areas inside the pores. By gradually increasing the voltage up to 10V, the emission extends to the areas around the pores. At voltages higher than 10V, a non-reversible nanopixel to nanoring-like switching of the electroluminescence can be observed. After filling the pores with a second blue-emitting conjugated polymer, voltage-dependent reversible color tuning of the electroluminescence is achieved in the nanostructured light-emitting bilayers.
Varun Vohra; Francesco Galeotti; Umberto Giovanella; Wojciech Mróz; Mariacecilia Pasini; Chiara Botta. Nanostructured Light-Emitting Polymer Thin Films and Devices Fabricated by the Environment-Friendly Push-Coating Technique. ACS Applied Materials & Interfaces 2018, 10, 11794 -11800.
AMA StyleVarun Vohra, Francesco Galeotti, Umberto Giovanella, Wojciech Mróz, Mariacecilia Pasini, Chiara Botta. Nanostructured Light-Emitting Polymer Thin Films and Devices Fabricated by the Environment-Friendly Push-Coating Technique. ACS Applied Materials & Interfaces. 2018; 10 (14):11794-11800.
Chicago/Turabian StyleVarun Vohra; Francesco Galeotti; Umberto Giovanella; Wojciech Mróz; Mariacecilia Pasini; Chiara Botta. 2018. "Nanostructured Light-Emitting Polymer Thin Films and Devices Fabricated by the Environment-Friendly Push-Coating Technique." ACS Applied Materials & Interfaces 10, no. 14: 11794-11800.
Facile detection and the identification of hazardous organic solvents are essential for ensuring global safety and avoiding harm to the environment caused by industrial wastes. Here, we present a simple method for the fabrication of silver-coated monodisperse polystyrene nanoparticle photonic structures that are embedded into a polydimethylsiloxane (PDMS) matrix. These hybrid materials exhibit a strong green iridescence with a reflectance peak at 550 nm that originates from the close-packed arrangement of the nanoparticles. This reflectance peak measured under Wulff-Bragg conditions displays a 20 to 50 nm red shift when the photonic sensors are exposed to five commonly employed and highly hazardous organic solvents. These red-shifts correlate well with PDMS swelling ratios using the various solvents, which suggests that the observable color variations result from an increase in the photonic crystal lattice parameter with a similar mechanism to the color modulation of the chameleon skin. Dynamic reflectance measurements enable the possibility of clearly identifying each of the tested solvents. Furthermore, as small amounts of hazardous solvents such as tetrahydrofuran can be detected even when mixed with water, the nanostructured solvent sensors we introduce here could have a major impact on global safety measures as innovative photonic technology for easily visualizing and identifying the presence of contaminants in water.
Ayaka Sato; Yuya Ikeda; Koichi Yamaguchi; Varun Vohra. Strongly Iridescent Hybrid Photonic Sensors Based on Self-Assembled Nanoparticles for Hazardous Solvent Detection. Nanomaterials 2018, 8, 169 .
AMA StyleAyaka Sato, Yuya Ikeda, Koichi Yamaguchi, Varun Vohra. Strongly Iridescent Hybrid Photonic Sensors Based on Self-Assembled Nanoparticles for Hazardous Solvent Detection. Nanomaterials. 2018; 8 (3):169.
Chicago/Turabian StyleAyaka Sato; Yuya Ikeda; Koichi Yamaguchi; Varun Vohra. 2018. "Strongly Iridescent Hybrid Photonic Sensors Based on Self-Assembled Nanoparticles for Hazardous Solvent Detection." Nanomaterials 8, no. 3: 169.
The preparation of water-processable nanoparticles (NPs) of polymer semiconductors assembled using an amphiphilic rod-coil block copolymer (BCP), and their application to active layer sustainable fabrication of organic photovoltaic devices are reported. The hydrophobic rod is a p-type semiconductor, while the hydrophilic coil is a short chain of poly-4-vinylpyridine strongly interacting with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). Through miniemulsion technique stable water-suspended blend NPs are obtained, avoiding nonconducting surfactant use. The amphiphilic BCP fulfills a dual function, as surfactant for stabilizing the blend NPs and as electron donor material in the active layer. After mild annealing of obtained films, blend NPs interconnect with each other forming compact and uniform layers with adequate morphology for efficient charge percolation to the electrodes. Space-charge limited hole mobility of ≈5 × 10−3 cm2 V−1 s−1 in BCP-only NP films annealed at 120 °C (corresponding to a tenfold increase in mobility as compared to the p-type semiconductor films spin-coated from chlorinated solvents) indicates strong p–p interactions in the self-assembled NPs. Blend NPs were covered with thin PC61BM layer and used as active layers in photovoltaic devices displaying high photocurrents (11.5 mA cm−2) and average power conversion efficiency of 2.53% after annealing at 90 °C.
Stefania Zappia; Guido Scavia; Anna Maria Ferretti; Umberto Giovanella; Varun Vohra; Silvia Destri. Water-Processable Amphiphilic Low Band Gap Block Copolymer:Fullerene Blend Nanoparticles as Alternative Sustainable Approach for Organic Solar Cells. Advanced Sustainable Systems 2018, 2, 1 .
AMA StyleStefania Zappia, Guido Scavia, Anna Maria Ferretti, Umberto Giovanella, Varun Vohra, Silvia Destri. Water-Processable Amphiphilic Low Band Gap Block Copolymer:Fullerene Blend Nanoparticles as Alternative Sustainable Approach for Organic Solar Cells. Advanced Sustainable Systems. 2018; 2 (3):1.
Chicago/Turabian StyleStefania Zappia; Guido Scavia; Anna Maria Ferretti; Umberto Giovanella; Varun Vohra; Silvia Destri. 2018. "Water-Processable Amphiphilic Low Band Gap Block Copolymer:Fullerene Blend Nanoparticles as Alternative Sustainable Approach for Organic Solar Cells." Advanced Sustainable Systems 2, no. 3: 1.
Due to their macromolecular nature, conjugated polymers can be relatively easily aligned by applying a variety of processes resulting in either elongation or ordering of their conjugated backbones. Processes that induce chain alignment include electrospinning, mechanical rubbing, epitaxial growth, and nanoconfinement and unidirectional deposition techniques such as off-center spin-coating. In this study, we compare these deposition techniques by applying them to a green-emitting conjugated polymer material that exhibits liquid crystalline phase behavior. Our study reveals that while methods such as electrospinning and mechanical rubbing can be useful to locally generate polymer chain alignment, the combination of epitaxial growth using 1,3,5-trichlorobenzene as crystallizing agent with off-center spin-coating results in the formation of anisotropic nanofiber-like structures with enhanced crystallinity degree and polarized light-emission properties. The unidirectional epitaxial growth was also applied to a red-emitting polymer that exhibits polarization ratios up to 4.1. Our results emphasize that this simple solution formulation and process can be used for the fabrication of polarized thin films of a variety of conjugated polymers with potential applications in the advanced display technologies or analytical equipment fields.
Takuya Anzai; William Porzio; Varun Vohra. Polarized Emission from Conjugated Polymer Chains Aligned by Epitaxial Growth during Off-Center Spin-Coating. Journal of Chemistry 2017, 2017, 1 -9.
AMA StyleTakuya Anzai, William Porzio, Varun Vohra. Polarized Emission from Conjugated Polymer Chains Aligned by Epitaxial Growth during Off-Center Spin-Coating. Journal of Chemistry. 2017; 2017 ():1-9.
Chicago/Turabian StyleTakuya Anzai; William Porzio; Varun Vohra. 2017. "Polarized Emission from Conjugated Polymer Chains Aligned by Epitaxial Growth during Off-Center Spin-Coating." Journal of Chemistry 2017, no. : 1-9.
Recent studies have demonstrated the advantage of developing pressure-sensitive devices with light-emitting properties for direct visualization of pressure distribution, potential application to next generation touch panels and human-machine interfaces. To ensure that this technology is available to everyone, its production cost should be kept as low as possible. Here, simple device concepts, namely, pressure sensitive flexible hybrid electrodes and OLED architecture, are used to produce low-cost resistive or light-emitting pressure sensors. Additionally, integrating solution-processed self-assembled micro-structures into the flexible hybrid electrodes composed of an elastomer and conductive materials results in enhanced device performances either in terms of pressure or spatial distribution sensitivity. For instance, based on the pressure applied, the measured values for the resistances of pressure sensors range from a few MΩ down to 500 Ω. On the other hand, unlike their evaporated equivalents, the combination of solution-processed flexible electrodes with an inverted OLED architectures display bright green emission when a pressure over 200 kPa is applied. At a bias of 3 V, their luminance can be tuned by applying a higher pressure of 500 kPa. Consequently, features such as fingernails and fingertips can be clearly distinguished from one another in these long-lasting low-cost devices.
Rie Shimotsu; Takahiro Takumi; Varun Vohra. All solution-processed micro-structured flexible electrodes for low-cost light-emitting pressure sensors fabrication. Scientific Reports 2017, 7, 6921 .
AMA StyleRie Shimotsu, Takahiro Takumi, Varun Vohra. All solution-processed micro-structured flexible electrodes for low-cost light-emitting pressure sensors fabrication. Scientific Reports. 2017; 7 (1):6921.
Chicago/Turabian StyleRie Shimotsu; Takahiro Takumi; Varun Vohra. 2017. "All solution-processed micro-structured flexible electrodes for low-cost light-emitting pressure sensors fabrication." Scientific Reports 7, no. 1: 6921.
Because of both its easy processability and compatibility with roll-to-roll processes, polymer electronics is considered to be the most promising technology for the future generation of low-cost electronic devices such as light-emitting diodes and solar cells. However, the state-of-the-art deposition technique for polymer electronics (spin-coating) generates a high volume of chlorinated solution wastes during the active layer fabrication. Here, we demonstrate that devices with similar or higher performances can be manufactured using the push-coating technique in which a poly(dimethylsiloxane) (PDMS) layer is simply laid over a very small amount of solution (less than 1μL/covered cm2), which is then left for drying. Using mm thick PDMS provides a means to control the solvent diffusion kinetics (sorption/retention) and removes the necessity for additional applied pressure to generate the desired active layer thickness. Unlike spin-coating, push-coating is a slow drying process that induces a higher degree of crystallinity in the polymer thin film without the necessity for a post-annealing step. The polymer light-emitting diodes and solar cells prepared by push-coating exhibit slightly higher performances with respect to the reference spin-coated devices, whereas at the same time reduce the amounts of active layer materials and chlorinated solvents by 50 and 20 times, respectively. These increased performances can be correlated to the higher polymer crystallinities obtained without applying a post-annealing treatment. As push-coating is a roll-to-roll compatible method, the results presented here open the path to low-cost and eco-friendly fabrication of a wide range of emerging devices based on conjugated polymer materials.
Varun Vohra; Wojciech Mroz; Shusei Inaba; William Porzio; Umberto Giovanella; Francesco Galeotti. Low-Cost and Green Fabrication of Polymer Electronic Devices by Push-Coating of the Polymer Active Layers. ACS Applied Materials & Interfaces 2017, 9, 25434 -25444.
AMA StyleVarun Vohra, Wojciech Mroz, Shusei Inaba, William Porzio, Umberto Giovanella, Francesco Galeotti. Low-Cost and Green Fabrication of Polymer Electronic Devices by Push-Coating of the Polymer Active Layers. ACS Applied Materials & Interfaces. 2017; 9 (30):25434-25444.
Chicago/Turabian StyleVarun Vohra; Wojciech Mroz; Shusei Inaba; William Porzio; Umberto Giovanella; Francesco Galeotti. 2017. "Low-Cost and Green Fabrication of Polymer Electronic Devices by Push-Coating of the Polymer Active Layers." ACS Applied Materials & Interfaces 9, no. 30: 25434-25444.