Bifunctional Ultrathin PCBM Enables Passivated Trap States and Cascaded Energy Level toward Efficient Inverted Perovskite Solar Cells
Dongyang Li, Weiguang Kong, Haichao Zhang, Deng Wang, Wang Li, Changwen Liu, Hong Chen, Weidong Song, Fangliang Gao, Abbas Amini, Baomin Xu, Shuti Li, Chun Cheng
Abstract
Inverted perovskite solar cells (PSCs) with a C60 framework are known for their common drawback of low power conversion efficiency (PCE) of <20% because of nonradiative recombination and inefficient charge transport at their perovskite interfaces. Here, we report an ultrathin [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a cap layer on perovskite films to overcome this issue. Such a functional cap layer efficiently passivates trap states and establishes a gradient energy level alignment onto perovskite, facilitating the efficient charge transfer and extraction. The as-fabricated inverted PSCs capped with such ultrathin PCBM exhibit a record PCE of 20.07%. After the storage under a N2 atmosphere for more than 500 h, the PCE of PSCs retains over 85% of its initial level. Our work provides an effective method to upgrade inverted PSCs with the C60 framework with improved efficiency and stability.