Integrating Ultrathin Bulk-Heterojunction Organic Semiconductor Intermediary for High-Performance Low- Bandgap Perovskite Solar Cells with Low Energy Loss
Guiying Xu1, Pengqing Bi2, Shuhui Wang1, Rongming Xue1, Jingwen Zhang1, Haiyang Chen1, Weijie Chen1, Xiaotao Hao2, Yaowen Li1，*（李耀文）, and Yongfang Li1,3
1State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials，Laboratory of Advanced Optoelectronic Materials，College of Chemistry，Chemical Engineering and Materials Science
Soochow University，Suzhou 215123, China
2School of Physics and State Key Laboratory of Crystal Materials，Shandong University，Jinan, Shandong 250100, China
3Beijing National Laboratory for Molecular Sciences Institute of Chemistry Chinese Academy of Sciences，Beijing 100190, China
Adv. Funct. Mater. 2018, 28, 1804427
Mixed tin (Sn)–lead (Pb) perovskite is considered the most promising lowbandgap photovoltaic material for both pursuing the theoretical limiting efficiency of single-junction solar cells and breaking the Shockley–Queisser limitation by constructing tandem solar cells. However, their power conversion efficiencies (PCEs) are still lagging behind those of medium-bandgap perovskite solar cells (pero-SCs) due to their serious energy loss (Eloss). Here, an ultrathin bulk-heterojunction (BHJ) organic semiconductor (PBDB-T:ITIC) layer is used as an intermediary between the hole transporting layer and Sn– Pb-based low-bandgap perovskite film to minimize Eloss. It is found that this BHJ PBDB-T:ITIC intermediary simultaneously provided a cascading energy alignment in the device, facilitated high-quality Sn–Pb perovskite film growth, and passivated the antisite defects of the perovskite surface. In this simple way, the Eloss of pero-SCs based on (FASnI3)0.6(MAPbI3)0.4 (bandgap ≈1.25 eV) is dramatically reduced below 0.4 eV, leading to a high open-circuit voltage (Voc) of 0.86 V. As a result, the best pero-SC showed a significantly improved PCE of 18.03% with negligible J–V hysteresis and high stability. As far as it is known, the PCE of 18.03% and Voc of 0.86 V are the highest values among the low-bandgap pero-SCs to date.