Water-Free, Conductive Hole Transport Layer for Reproducible Perovskite–Perovskite Tandems with Record Fill Factor
Md Arafat Mahmud, Jianghui Zheng, Shi Tang, Chwenhaw Liao, Guoliang Wang, Jueming Bing, Tik Lun Leung, Anh Dinh Bui, Hongjun Chen, Jianpeng Yi, Stephen Bremner, Hieu T. Nguyen, Anita Ho‐Baillie
Abstract
State-of-the-art perovskite–perovskite tandem solar cells incorporate a water-based poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole transport layer in its low bandgap subcell. However, there is a limitation regarding its use due to the moisture sensitivity of perovskites and the insulating property of PSS. Here, we overcome the limitation by using a water-free and PSS-free PEDOT-based hole transport layer for low bandgap single-junction perovskite solar cells and in perovskite–perovskite tandems. The champion tandem cell produces an efficiency of 21.5% and a fill factor of 85.8%, the highest for any perovskite-based double-junction tandems. Results of photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and conductive atomic force microscopy reveal evidence of enhanced conductivity of water-free and PSS-free PEDOT compared to its conventional counterpart. The use of water-free and PSS-free PEDOT also eliminates decomposition of high bandgap subcell with its interfacing layer stack in a tandem that otherwise occurs with conventional PEDOT:PSS. This leads to enhanced reproducibility of perovskite–perovskite tandems.