Homogeneous and Graded Ag Alloying in (Cu_1‐xAg_x)₂ZnSnSe₄ Solar Cells

Abstract

Cu 2 ZnSn(S,Se) 4 (CZTSSE)-based solar cell performances are limited by band tailing due to a large amount of Cu Zn antisite defects. Partially replacing the Cu atoms by larger Ag ones can significantly reduce the prevalence of these defects, which are particularly detrimental close to the front interface. Herein, the possibility of synthesizing (Cu 1-x Ag x) 2 ZnSnSe 4 absorbers with various Ag contents by vacuum-based processes is demonstrated. Although the synthesis of high-quality materials is demonstrated, their use in thin film photovoltaic devices does not exhibit performance improvement compared with efficient pure CZTSSE-based solar cells. Moreover, the comparison with literature data reopens the debate of the beneficial effect of homogeneous Ag alloying in kesterite. On the contrary, a new method is proposed to fabricate graded (Cu 1-x Ag x) 2 ZnSnSe 4 absorbers with increased Ag content at the interfaces. The solar cells with graded absorbers exhibit better performances than the reference Ag-free ones. Particularly, improved current collection at the back contact and slight reduction of the front interface recombination are demonstrated.

Effect of Pre‐annealing Treatment on Growth and Properties of (Cu0.5Ag0.5)2ZnSnSe4 Thin Films

“…So far, limited reports have been accessible on Ag alloying in CZTSe thin films and its device performance, where twostep methods were adopted for the preparation of Ag-alloyed CZTSe thin films comprising of deposition of metallic thin films by physical and chemical techniques such as sputtering, solution proceeds, co-evaporation, and thermal evaporation followed by annealing/selenization at elevated temperature (≥500 °C). [1,[28][29][30][32][33][34][35][36][37] However, due to the high diffusivity of silver at high temperatures, it rapidly distributes throughout the depth of the CAZTSe films and it is difficult to control its uniform distribution across the film thickness at elevated temperatures. [28] In this connection, low-temperature selenization (≤480 °C) was explored for the uniform distribution of Ag in CZTSe thin films.…”