Reducing Energy Disorder of Hole Transport Layer by Charge Transfer Complex for High Performance p–i–n Perovskite Solar Cells
Guiying Xu1, Rongming Xue1, Samuel J. Stuard2, Harald Ade2, Chenjie Zhang1, Jianlin Yao1, Yaowen Li1, *（李耀文）, and Yongfang Li1,3
1 Laboratory of Advanced Optoelectronic Materials，College of Chemistry Chemical Engineering and Materials Science，Soochow University，Suzhou 215123, China
2Department of Physics and Organic and Carbon Electronic Laboratories (ORaCEL)，North Carolina State University，Raleigh, NC 27695, USA
3Beijing National Laboratory for Molecular Sciences Institute of Chemistry，Chinese Academy of Sciences，Beijing 100190, China
Adv. Mater. 2021, 2006753
Solution‐processed organic semiconductor charge‐transport layers (OS‐CTLs) with high mobility, low trap density, and energy level alignment have dominated the important progress in p–i–n planar perovskite solar cells (pero‐SCs). Unfortunately, their inevitable long chains result in weak molecular stacking, which is likely to generate high energy disorder and deteriorate the charge‐transport ability of OS‐CTLs. Here, a charge‐transfer complex (CTC) strategy to reduce the energy disorder in the OS‐CTLs by doping an organic semiconductor, 4,4′‐(4,8‐bis(5‐(trimethylsilyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(N,N‐bis(4‐methoxyphenyl)aniline) (BDT‐Si), in a commercial hole‐transport layer (HTL), poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl)amine (PTAA), is proposed. The formation of the CTC makes the PTAA conjugated backbone electron‐deficient, resulting in a quinoidal and stiffer character, which is likely to planarize the PTAA backbone and enhance the ordering of the film in nanoscale. The resultant HTL exhibits a reduced energy disorder, which simultaneously promotes hole transport in the HTL, hole extraction at the interface, energy level alignment, and quasi‐Fermi level splitting in the device. As a result, the p–i–n planar pero‐SCs with optimized HTL exhibit the best power conversion efficiency of 21.87% with good operating stability. This finding demonstrates that the CTC strategy is an effective way to reduce the energy disorder in HTLs and to improve the performance of planar pero‐SCs.