CIS solar cells with ZnO buffer layers

This paper describes investigations of CIS solar cells with ZnO buffer layers. Studies concentrate on determining optimum ZnO buffer layer properties that will yield the maximum ZnO/CIS solar cell efficiency. Buffer layers are grown by chemical vapor deposition (CVD) by reacting a zinc adduct with tetrahydrofuran to grow ZnO. Substrate temperatures (T_sub) have been varied from 100°C to 350°C, with the best device performance obtained for T_sub≈225°C to 250°C. ZnO/CIS solar cells were fabricated by first depositing a ZnO buffer layer, followed by deposition of a low resistivity ZnO top contact layer and a Al/Ag collector grid. Several cells have been fabricated with an area of 0.44 cm² that have total area efficiencies greater than 11%. In particular, a cell was fabricated with a Siemens substrate that exhibited a total area efficiency of 11.3%, and one based on a NREL substrate that has a total area efficiency of 12%. This work has focused on determining optimum deposition parameters for CVD ZnO buffer layers. It is clear that in order to achieve efficient ZnO/CIS cells, the buffer layer must be deposited with a high resistivity