A review on the fundamental understanding and rational design of ideal, dopant-free HTMs for fabricating efficient and stable perovskite solar cells.

New ternary composites of MnO2 nanorods, polyaniline (PANI) and graphene oxide (GO) have been prepared by a two-step process. The 100 nm-long MnO2 nanorods with a diameter ~20 nm are conformably coated with PANI layers and fastened between GO layers. The MnO2 nanorods incorporated ternary composites electrode exhibits significantly increased specific capacitance than PANI/GO binary composite in supercapacitors. The ternary composite with 70% MnO2 exhibits a highest specific capacitance reaching 512 F/g and outstanding cycling performance, with ~97% capacitance retained over 5000 cycles. The ternary composite approach offers an effective solution to enhance the device performance of metal-oxide based supercapacitors for long cycling applications.

Layer-by-layer (LbL) solution processing is a cost-effective technology for the large-scale fabrication of organic solar cells (OSCs). In this work, LbL OSCs were fabricated using PTQ10/J71 as donors and ITC6-IC/IDIC/MeIC/ITCPTC/ITIC as non-fullerene acceptors (NFAs) without using orthogonal solvents and appropriate co-solvents. Compared with traditional bulk heterojunction (BHJ) OSCs, the corresponding solution-processed LbL devices exhibited higher or comparable power conversion efficiencies (PCEs), which had the advantages of reduced energy loss, stronger absorption spectra, better vertical phase separation, partially increased charge transport property and charge collection efficiency. Furthermore, taking the J71/ITC6-IC and PTQ10/IDIC LbL systems as examples, we fabricated large-area LbL OSCs using the doctor-blading process, which is closer to the roll-to-roll (R2R) technology. Importantly, both OSCs based on J71/ITC6-IC and PTQ10/IDIC LbL with an active area of 1.00 cm² demonstrated encouraging PCEs of over 10%, which is the record efficiency for large-area LbL OSCs reported in the literature to date. Our work indicates that the solution-processed LbL approach not only presents good generality and high device performance, but also is a superior alternative to the BHJ method for the initial evaluation of photovoltaic materials and the industrial production of R2R OSCs.

Highly efficient ternary polymer solar cells (PSCs) are fabricated from two well-compatible small molecular nonfullerene acceptors (INPIC-4F and MeIC1) and one polymer donor, PBDB-T. The power conversion efficiency (PCE) of the INPIC-4F or MeIC1 based binary PSCs reaches 12.55% and 11.53%. Based on these efficient binary PSCs, a high PCE of 13.73% is achieved in the ternary PSCs with 50 wt% MeIC1 in the acceptors, resulting from the simultaneously improved short circuit current (J_SC) of 21.86 mA cm⁻², open circuit voltage (V_OC) of 0.88 V and fill factor (FF) of 71.39%. The PCE improvement of the ternary PSCs should be mainly attributed to the simultaneously optimized photon harvesting and film morphology of the ternary active layers. This result may provide more in-depth insight into the material selection criteria for fabricating highly efficient ternary PSCs: (i) the complementary absorption spectra and good compatibility of the used materials; (ii) the complementary photovoltaic parameters of the corresponding two binary PSCs.