Control of aggregation and dissolution of small molecule hole transport layers via a doping strategy for highly efficient perovskite solar cells

Abstract

Recently, small molecule hole transporting layers (HTLs) have attracted growing interest in perovskite solar cells due to their low-cost, excellent stability, and better energy level alignment with the perovskites. Nonetheless, an amorphous and coarse surface film is one of the main obstructions to the performance of these small molecule HTLs. Herein, a small molecule, namely, N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) was doped with a polymer to overcome the formation of molecular aggregation in an HTL. This polymer doping strategy resulted in a very smooth surface, which improved the photo-physical and electrochemical properties at the HTL/perovskite interface. Consequently, a maximum power conversion efficiency (PCE) of 17.80%, 32% higher than that of the control, i.e., the NPB-based device (13.57%), has been achieved. This study reveals the critical influence of molecular aggregations on the performance of perovskite solar cells, which impairs the development of an efficient device based on small molecule HTLs.