Design of High-Performance Photovoltaic Materials via Codoping of Cs₂AgPdX₅ (X = Cl, Br)

In the realm of photovoltaic applications, the quest to replace toxic lead halide perovskites has led to the design of double perovskites. A recent breakthrough has emerged with the synthesis of Cs₂AgPdX₅ (X = Cl, Br) double perovskites exhibiting intriguing 1D electronic dimensionality. However, these materials still face challenges with their indirect band gap and low optical absorption, rendering them less desirable for solar cells. In this study, on the basis of first-principles calculations, we propose to employ doping strategies to overcome these limitations. Introducing IIB elements (Zn, Cd, and Hg) yields a direct or quasi-direct band gap, while doping IIIA elements (Ga, In) significantly enhances optical absorption. Interestingly, the former is a geometric effect and the latter is an electronic effect. Therefore, they can be straightforwardly combined and codoping IIB and IIIA elements leads to a favorable band gap (1.00–1.68 eV) and at the same time a strong optical absorption. Remarkably, the codoped systems Cd–In–Cs₂AgPdCl₅ and Cd–In–Cs₂AgPdBr₅ show an exceptionally high power conversion efficiency of up to 30%. These findings open a new avenue for photovoltaic material design.