The potential of textured front ZnO and flat TCO/metal back contact to improve optical absorption in thin Cu(In,Ga)Se2 solar cells

The role of additionally textured front transparent conductive oxide - TCO (ZnO:Al) and flat TCO/metal contact on optical improvements in thin Cu(In,Ga)Se, (CIGS) solar cells are investigated by means of numerical simulations.A de-coupled analysis of two effects related to additional texturing of front surface of ZnO:Al TCO - (i) enhancement of light scattering and (ii) decreased total reflectance (antireflective effect) - reveals that the improvements in quantum efficiency, QE, and short-circuit current, J(SC), of the solar cell originate from an antireflective effect only. In order to improve optical properties of the back contact the introduction of a TCO layer (undoped ZnO) between CIGS and back metal contact is investigated from the optical point of view. In addition to ZnO/Mo, a highly reflective ZnO/Ag contact (ZnO is also assumed to work as a protection layer for Ag) is also included in simulations. Results show significant increase in reflectance related to introduced ZnO in front of Mo. Drastically increased reflectance is obtained if ZnO/Mo is substituted with ZnO/Ag. The improvements in QE and J(SC) of a thin CIGS solar cell, related to ZnO/metal contacts are presented. (C) 2006 Elsevier B.V. All rights reserved.