All-Solution-Processed Cu2ZnSnS4 Solar Cells with Self-Depleted Na2S Back Contact Modification Layer

Abstract

The thin‐film photovoltaic material Cu2ZnSnS4 (CZTS) has drawn worldwide attention in recent years due to its earth‐abundant, nontoxic element constitution, and remarkable photovoltaic performance. Although state‐of‐the‐art power conversion efficiency is achieved by hydrazine‐based methods, effort to fabricate such devices in a high throughput, environmental‐friendly way is still highlydesired. Here a hydrazine‐free all‐solution‐processed CZTS solar cell with Na2S self‐depleted back contact modification layer for the first time is demonstrated, using a ball‐milled CZTS as light absorber, low‐temperature solution‐processed ZnO electron‐transport layer as well as silver‐nanowire transparent electrode. The inserting of Na2S self‐depleted layer is proven to effectively stabilize the CZTS/Mo interface by eliminating a detrimental phase segregation reaction between CZTS and Mo‐coated soda lime glass, thus leading to a better crystallinity of CZTS light absorbing layer, enhanced carrier transportation at CZTS/Mo interface as well as a smaller series resistance. Furthermore, the self‐depletion feature of the Na2S modification layer also averts hole‐transportation barrier within the devices. The results show the vital importance of interfacial engineering for these CZST devices and the Na2S interface layer can be extended to other optoelectronic devices using Mo contact. Show more