CdTe single-crystal heterojunction photovoltaic cells

Most recent gains in CdTe photovoltaic (PV) device efficiency have been in short-circuit current density (J_sc) and fill factor (FF), rather than open-circuit voltage (V_oc). Because J_sc is nearing its theoretical limit, further improvements in device efficiency will require increasing V_oc beyond 860 mV and increasing FF. V_oc and FF may be improved by increasing both the carrier concentration and minority-carrier lifetime of the CdTe. However, V_oc may be limited for other reasons, including Fermi-level pinning and surface recombination. In this study, we used doped CdTe single crystals to test whether higher carrier concentration and lifetime can overcome traditional V_oc barriers. In our work to date, we have fabricated heterojunction CdTe PV cells with V_oc up to 929 mV, FF of ~60%, and efficiencies of 10%.