Single crystal elasticity constants of CuIn1-xGaxSe2 thin films for photovoltaic solar cells applications

Thin-films photovoltaic solar cells involving Cu(In_1-x, Ga_x)Se₂ (CIGS) have attracted much attention since they showed conversion efficiencies exceeding 20 %. However, they still suffer from a lack of stability. Extensive studies have been focused on the degradation of CIGS absorbers under light, humidity and thermal loading. However, only limited studies were conducted on mechanical stress gradients generated in CIGS absorber from fabrication and during service and its contribution to cell degradation. To quantify the residual stress gradients, X-ray elasticity constants (XEC) of CIGS are needed. However, the single crystal elasticity constants (SCEC) of CIGS are not known. This study focuses on the determination of the SCEC of CIGS. The SCEC were determined through inverse method by coupling in-situ four point bending laboratory X-ray diffraction and micro-mechanical modelling. The anisotropy and crystallographic texture were taken into account. The SCEC will permit the quantification of residual stress gradients and its evolution. It will allow a better understanding of the chemical and mechanical coupling that could appear in CIGS during degradation.