Heinemann, M.D.; Ruske, F.; Greiner, D.; Jeong, A.R.; Rusu, M.; Rech, B.; Schlatmann, R.; Kaufmann, C.A.: Advantageous light management in Cu(In,Ga)Se2 superstrate solar cells. Solar Energy Materials and Solar Cells 150 (2016), p. 76-81
10.1016/j.solmat.2016.02.005

Abstract:
The superstrate configuration of Cu(In,Ga)Se2 (CIGS) photovoltaic devices exhibits the potential for improved light harvesting compared to the standard substrate configuration. Due to the limited power conversion efficiency of superstrate devices caused by the poor hetero-interface between the p-type CIGS and the n-type component, these advantages have not been fully considered so far. This work shows that the superstrate configuration can significantly improve the light management within CIGS devices. Experimentally, it is shown that the electric and optical properties of ZnO window layer strongly improve during the CIGS deposition, allowing the use of structured ZnO layers for efficient light-trapping. A highly reflective and scattering back contact is realized by using the high work function material MoO3−x for the hole-transport layer in combination with a low work function Ag metal layer. Combined with the unique Ga gradient achievable in the superstrate configuration, simulation results show that a strong reduction of the CIGS layer thickness is possible while increasing the power conversion efficiency. This proof of concept highlights the appeal of the superstrate configuration for the future of cost-effective CIGS solar cell production.