Homogeneous and Graded Ag Alloying in (Cu1‐xAgx)2ZnSnSe4 Solar Cells. Issue 9 (11th March 2020) - Grenet, Louis
Abstract : Cu2 ZnSn(S, Se)4 (CZTSSE)‐based solar cell performances are limited by band tailing due to a large amount of CuZn 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 (Cu1‐ x Ag x )2 ZnSnSe4 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 (Cu1‐ x Ag x )2 ZnSnSe4 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. Abstract : The synthesis of homogeneous and high‐quality (Cu1‐ x Ag x )ZnSnSe4 absorbers with 0 ≤ x ≤ 50% is demonstrated. However, performances of solar cells decrease with increasing Ag content in the absorber. Absorbers with graded compositions are fabricated as well. Increasing the Ag content toward the interfaces allows to improve the carrier collection and reduce recombination. Thus, the device performance is improved.