Dopant-free hole transport materials based on alkyl-substituted indacenodithiophene for planar perovskite solar cells

Xiaoyuan Liu, Ehsan Rezaee, Haiquan Shan, Jiaju Xu, Yin Zhang, Yaomiao Feng, Junfeng Dai, Zhi Kuan Chen, Wei Huang, Zong Xiang Xu