Synergistic Interface Energy Band Alignment Optimization and Defect Passivation toward Efficient and Simple-Structured Perovskite Solar Cell

Efficient electron transport layer-free perovskite solar cells (ETL-free PSCs) with cost-effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small-molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier-free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state-of-the-art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL-free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification

Efficient planar heterojunction perovskite solar cells with enhanced FTO/SnO2 interface electronic coupling

Ultrathin and compact SnOx amorphous layers derived from SnCl4 were introduced at the interface of electron transport layer (ETL)/perovskite or FTO/ETL to enhance the electron coupling between layers, passivate the trapping defects and optimize the energy level alignment. As results of the increased interface electron collection and reduced interface recombination, the planer perovskite solar cell (PSC) with SnO2 nanocrystal (NC) ETL pre-treated by SnCl4 (Cl-SnO2) shows the power conversion efficiency (PCE) enhancement from 16.3% to 18.6%, and the device hysteresis has also been significantly restrained. In comparison, the planer PSCs with traditional SnCl4 (SnO2-Cl) post-treated SnO2 NC ETL makes the PCE increased from 16.3% to 17.3%. These results indicate that both two kinds of treated ways could improve the performance of the PSCs but compared with the post-treatment process, the devices based on Cl-SnO2 pre-treated ETL present superior performance, which is attributed to the closer contact and enhanced electron coupling between FTO and SnO2 NC ETL with Cl-SnO2 in between. (C) 2020 Published by Elsevier B.V