Zhaojie Zhang1,Hamza Javaid1,Emily Smith1,Dhandapani Venkataraman1
University of Massachusetts, Amherst1
Zhaojie Zhang1,Hamza Javaid1,Emily Smith1,Dhandapani Venkataraman1
University of Massachusetts, Amherst1
Copper halides are promising hole transport materials for inverted perovskite solar cells (PSCs) due to their advantages of low cost, tunable energy levels, good hole mobility, and excellent stability. However, the understanding of the role of mixed copper halides with fine-tuned energy levels and conducting properties in highly efficient inverted PSCs is still unclear. Here, we demonstrate that using CuI<sub>x</sub>Br<sub>1-x</sub> with an optimized Br/I ratio as HTL leads to a champion power conversion efficiency of 19.2% compared to PTAA (17.7%), CuI (16.6%), and CuBr (17.6%) based PSCs. We systematically investigate the influence of electronic properties of CuI<sub>x</sub>Br<sub>1-x</sub>, including hole mobility, hole density, energy level, and band gap on the performance (V<sub>oc</sub>, J<sub>sc</sub>, and FF) and stability of PSCs. We used hyperspectral photoluminescence imaging to quantify charge carrier transport dynamics and recombination loss. PSCs with fine-tuned CuI<sub>x</sub>Br<sub>1-x</sub> have a more homogeneous distribution of quasi-fermi level splitting and more efficient charge extraction, leading to improved fill factor. CuI<sub>x</sub>Br<sub>1-x</sub> also suppresses ion migration and phase segregation in mixed-halide perovskite films. This work provides design guidelines for improving the performance and stability of PSCs by tuning the electronic properties of hole transport layers.