ZnO nanowire based CIGS solar cell and its efficiency enhancement by the piezo-phototronic effect

Cu(In,Ga)Se-2(CIGS)-based heterostructures have been thought to be one of the most prospective thin film solar cells. However, considering cost competitiveness, researchers are still seeking for new methods to improve the power conversion efficiency (PCE). In this work, the ZnO nanowires are first introduced into the CIGS-based solar cells to substitute the ZnO film for well developing the piezoelectric effect. Interestingly, the solar cells exhibit very good photovoltaic performances with PCE of 9.83% for rigid device and 5.43% for flexible device, the PCE of which is even larger than that of the corresponding ZnO film CIGS devices. Moreover, by exerting piezo-phototronic effect of the ZnO nanowires, the PCE of the rigid device is modulated from 9.83% to 11.40% with vertical pressure increasing from 0 to 2 MPa, and the PCE of the flexible device improves from 4.82% to 5.96% with external strain changing from a 0.74% tensile strain to a -0.74% compressive strain. This study demonstrates that introducing ZnO nanowires as well as the associated piezo-phototronic effect provides an ideal approach for improving the performances of CIGS-based solar cells.