Research On Novel Photoanode Charge Transport Properties Of Perovskite Solar Cells

Perovskite solar cells have becomed a hotspot for research, because of its simple process and low cost. It is a very big enhancement that the efficiency is increase from 3.9% to 20.1% since 2009. Planar heterojunction perovskite solar cells have the advantages of simple structure which made it become a hotspot for research, but the hysteresis phenomenon is serious. Mesoporous perovskite solar cells structure is complex and the hysteretic phenomena is not as severe as planar heterojunction perovskite solar cells, but it has serious charge recombination. This paper intends to explore a way to improve the performance of the perovskite solar.We present here planar heterojunction perovskite solar cells employing α-Fe₂O₃ as electron transporting layer（ETL）, exhibiting non-obvious hysteresis characteristics and higher steady-state power conversion efficiency（PCE） compared to the conventional TiO₂ based device. It is attributed to the higher built in potential across the perovskite layer in the device with α-Fe₂O₃ ETL, leading to more efficient charge extraction/transport and less charge recombination than that using TiO₂ ETL, as evidenced by higher steady-state photocurrent. As a consequence, a significant reduction in the charge accumulation at the perovskite/α-Fe₂O₃ interface makes the J-V test much less sensitive to scanning rate and direction. Furthermore, α-Fe₂O₃ based devices display good stability over 30 days of storage time with exposure to the ambient air, the efficiency is reduced by about 5%, which is ascribed to more hydrophobic of α-Fe₂O₃ than that of TiO₂.Thermoelectric NaCo₂O₄ nanofibers coated with a thin layer of TiO₂ nanoparticles（NaCo₂O₄/TiO₂） are randomly distributed in the m-TiO₂ layer as composite photoanodes for PSCs. The NaCo₂O₄/TiO₂ core/shell nanocable structure provided increased interface to facilitate electrons transfer from m-TiO₂ to NaCo₂O₄ with high charge mobility. Our results indicate that NaCo₂O₄ can convert heat generated in the photoanode to thermo-electromotive force to promote the electron transport and collection, and thus suppress the charge recombination.The electron injection efficiency was also found to be significantly improved. The best power conversion efficiency（PCE） was achieved in a PSC device with 9.1wt% NaCo₂O₄/TiO₂, which is mainly attributing to the increased short circuit current density（Jsc） and consequently result in an overall PCE improvement of ²0%.