Rare earth ions doped NiO hole transport layer for efficient and stable inverted perovskite solar cells

Hole transport layer plays a critical role in achieving high performance and stable inverted perovskite solar cells (PSCs). Doping has been proved to be an effective strategy to modify the electrical and optical properties of semiconductor oxides. Herein, rare earths (REs: Ce, Nd, Eu, Tb, and Yb) elements are systemically doped into the NiOx hole transport layer (HTL) via a simple solution-based method. The results demonstrate that the REs doping could considerably modify the compactness, conductivity, and band alignment of the NiOx HTL, leading to the highly improved permanence of the inverted PSCs. The PSCs using 3% Eu:NiOx HTL yielded the optimum power conversion efficiency of 15.06%, relatively improved 23.4% compared with the PSC using pristine NiOx HTL (12.20%). It also demonstrated much better long time stability. The improved photovoltaic properties of the device can be attributed to the more efficient charge extraction and suppressed interfacial recombination rate by the introduction of appropriate REs in the NiOx HTL. This work indicates that RE doping is a very effective and promising strategy to achieve adjustable hole extraction material for high and stable inverted PSCs.