Dopant-free hole transporting materials with supramolecular interactions and reverse diffusion for efficient and modular p-i-n perovskite solar cells
Rongming Xue1, Moyao Zhang1, Deying Luo2, Weijie Chen1, Rui Zhu2, Yang (Michael) Yang3, Yaowen Li1*（李耀文）& Yongfang Li1,4
1Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
2State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, China
3State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
4Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Sci China Chem, 63, 987--996(2020)
The rational design of dopant-free organic hole-transporting layer (HTL) materials is still a challenge for realizing high-efficient and stable p-i-n planar perovskite solar cells (pero-SCs). Here, we synthesized two π-conjugated small-molecule HTL materials through tailoring the backbone and conjugated side chain to carefully control molecular conformation. The resultant BDT-TPAsTh containing a planar fused benzo[1,2-b:4,5-b′]dithiophene (BDT) core and a conjugated thiophene side chain showed the planar conformation. X-ray crystallography showed a favorable stacking model in solid states under the parallel-displaced π-π and additional S-π weak-bond supramolecular interactions, thus achieving an obviously increased hole mobility without dopants. As an HTL material in p-i-n planar pero-SCs, the marginal solubility of BDT-TPA-sTh enabled inverse diffusion into the perovskite precursor solution for assisting the subsequent perovskite film growth and passivating the uncoordinated Pb2+ ion defects. As a result, the planar p-i-n pero-SCs exhibited a champion power conversion efficiency (PCE) of 20.5% and enhanced moisture stability. Importantly, the BDT-TPA-sTh HTL material also showed weak thickness-photovoltaic dependence, and the pero-SCs with blade-coated BDT-TPA-sTh as a HTL achieved a 15.30% PCE for the 1-cm2 modularized device. This HTL material design strategy is expected to pave the way toward high-performance, dopant-free and printing large-area planar p-i-n pero-SCs.