Enhanced Efficiency and Long-Term Stability of Perovskite Solar Cells by Synergistic Effect of Nonhygroscopic Doping in Conjugated Polymer-Based Hole-Transporting Layer

Abstract

A face-on oriented and p-doped semicrystalline conjugated polymer, poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c] [1,2,5]-thiadiazole) (PPDT2FBT), was studied as a hole transport layer (HTL) in methylammonium lead triioclidebased perovskite solar cells (PVSCs). PPDT2FBT exhibits a mid-band gap (1.7 eV), high vertical hole mobility (7.3 X 10(-3) cm(2)/V-s), and well-aligned frontier energy levels with a perovskite layer for efficient charge transfer/transport, showing a maximum power conversion efficiency (PCE) of 16.8%. Upon doping the PPDT2FBT HTL with a nonhygroscopic Lewis acid, tris(pentafluorophenyl)borane (BCF, 2-6 wt %), the vertical conductivity was improved by a factor of approximately 2, and the resulting PCE was further improved up to 17.7%, which is higher than that of standard PVSCs with 2,2',7,7'-tetralds(N,N-di-p-methoxyphenylamine)-9,9'-spirobilluorene (spiroOMeTAD) as an HTL. After BCF doping, the clearly enhanced carrier diffusion coefficient, diffusion length, and lifetime were measured using intensity-modulated photocurrent and photovoltage spectroscopy. Furthermore, compared to the standard PVSCs with spiro-OMeTAD, the temporal device stability was remarkably improved, preserving the similar to 60% of the original PCE for SOO h without encapsulation under light-soaking condition (1 sun AM 1.5G) at 85 degrees C and 85% humidity, which is mainly due to the highly crystalline conjugated backbone of PPDT2FBT and nonhygroscopic nature of BCF. In addition, formamidinium lead iodide/bromide (FAPbI(3-x)Br(x))-based PVSCs with the BCF-doped PPDT2FBT as an HTL was also prepared to show 18.8% PCE, suggesting a wide applicability of PPDT2FBT HTL for different types of PVSCs.,