Chapter 7 - Molybdenum back contact interface engineering of kesterite CZTSSe solar cells: Ultrathin intermediate engineering layers

Abstract

Back contact interface in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic device plays an important role in fabricating high quality of the semiconducting photoactive layer and improving carrier extraction efficiency. Unfortunately, the back contact interface between CZTSSe and Mo is chemically unstable during the high-temperature reactive annealing treatment process, which results in MoS(e)2 interface layer and secondary phases at the bottom of absorbing layer, deteriorating the photovoltaic performance of CZTSSe solar cell. In this chapter, insights into the key limiting factors of back contact and corresponding cutting-edge strategies are represented in detail, particularly focusing on the aspects of the composition of interface layer, energy band alignment, back electric field and interface passivation improvements. Moreover, the deeper understanding in kesterite photovoltaics involving these electrical limits are comprehensively discussed, and plausible promising directions for the future establishment of ideal back contact are also addressed.