Antimony triselenide (Sb₂Se₃) has become a very promising candidate for next-generation thin-film solar cells due to the merits of their low-cost, low-toxic and excellent optoelectronic properties. Despite Sb₂Se₃ thin-film photovoltaic technology having undergone rapid development over the past few years, insufficient doping concentration and severe recombination have been the most challenging limitations hindering further breakthroughs for the Sb₂Se₃ solar cells. Post-annealing treatment of the Sb₂Se₃/CdS heterojunction was demonstrated to be very helpful in improving the device performance previously. In this work, post-annealing treatments were applied to the Sb₂Se₃/CdS heterojunction under a vacuum and in the air, respectively. It was found that compared to the vacuum annealing scenario, the air-annealed device presented notable enhancements in open-circuit voltage. Ultimately a competitive power conversion efficiency of 7.62% was achieved for the champion device via air annealing. Key photovoltaic parameters of the Sb₂Se₃ solar cells were measured and the effects of post-annealing treatments using different scenarios on the devices were discussed.

This work explores the effect of a Zn_1−xSn_xO_y (ZTO) layer as a potential replacement for CdS in Sb₂(S,Se)₃ devices. Through the use of Afors-het software v2.5, it was determined that the ZTO/Sb₂(S,Se)₃ interface exhibits a lower conduction band offset (CBO) value of 0.34 eV compared to the CdS/Sb₂(S,Se)₃ interface. Lower photo-generated carrier recombination can be obtained at the interface of the ZTO/Sb₂(S,Se)₃ heterojunction. In addition, the valence band offset (VBO) value at the ZTO/Sb₂(S,Se)₃ interface increases to 1.55 eV. The ZTO layer increases the efficiency of the device from 7.56% to 11.45%. To further investigate the beneficial effect of the ZTO layer on the efficiency of the device, this goal has been achieved by five methods: changing the S content of the absorber, changing the thickness of the absorber, changing the carrier concentration of ZTO, using various Sn/(Zn+Sn) ratios in ZTO, and altering the thickness of the ZTO layer. When the S content in Sb₂(S,Se)₃ is around 60% and the carrier concentration is about 10¹⁸ cm⁻³, the efficiency is optimal. The optimal thickness of the Sb₂(S,Se)₃ absorber layer is 260 nm. A ZTO/Sb₂(S,Se)₃ interface with a Sn/(Zn+Sn) ratio of 0.18 exhibits a better CBO value. It is also found that a ZTO thickness of 20 nm is needed for the best efficiency.

The near-infrared (NIR) organic dyes with strong ultrafast nonlinear optical (NLO) activities are of importance for various applications. However, such kinds of dyes are still scarce. In this work, we have compared the NLO properties of two NIR Aza-BODIPY derivatives, in which the strong electron-donating groups, namely 4-(N, N-dimethylamino) phenyl and 1-ethyl-1,2,3,4-tetrahydroquinoline groups, are connected with the cores of Aza-BODIPY. Z-Scan experimental results show that two Aza-BODIPY derivatives exhibit strong saturation absorption and large modulation depth under the excitation of femtosecond pulses at 800 nm. Under 1300 nm excitation, two derivatives exhibit strong nonlinear refraction. In addition, the Aza-BODIPY derivatives also display effective two-photon excited fluorescence emission in the wavelength range of 1200-1600 nm. Based on the experimental results, it is found that 1-ethyl-1,2,3,4-tetrahydroquinoline group can more effectively enhance the NLO properties of Aza-BODIPY derivatives compared with the 4-(N, N-dimethylamino) phenyl group, thus providing new possibilities for the design and development of NIR NLO materials.

Near-infrared (NIR) organic dyes with strong ultrafast nonlinear optical (NLO) activities are important for various applications. However, the study of the wavelength-dependent NLO properties of NIR dyes is still ongoing. In this work, we present the first comparison of the NLO properties of two NIR boron-dipyrromethene (BODIPY) derivatives at different excitation wavelengths, in which strong electron-donating groups, namely 4-(N,N-dimethylamino)phenyl and 1-ethyl-1,2,3,4-tetrahydroquinoline groups, are connected through the BODIPY cores. Results obtained from Z-scan experiments show that the two BODIPY derivatives exhibit strong saturable absorption and large modulation depth when excited by femtosecond pulses at 800 nm. With 1300 nm excitation, both derivatives exhibit strong nonlinear refraction. In addition, the derivatives also display effective two-photon action cross-sections in the wavelength range of 1200–1600 nm. They are potentially excellent nonlinear optical materials. This comprehensive comparison of the NLO properties of BODIPY derivatives can suggest new possibilities for the design and development of NIR NLO materials.