Advances in CuInSe2 and CdTe thin film solar cells

Abstract

Research on CuInSe₂ and CdTe thin film solar cells is discussed. CuInSe₂ was deposited by selenization of Cu/In layers and was used to make a 10% efficient CuInSe₂/(CdZn)S cell. Characterization of the reaction mechanisms is described. The open-circuit voltage $\text{V}{}_{\mathrm{<mtext>oc</mtext>}}$ of CuInSe₂/(CdZn)S cells is dominated by recombination in the space charge region, so increasing the band gap or decreasing the width of this region should increase $\text{V}{}_{\mathrm{<mtext>oc</mtext>}}$. Increasing the band gap with a thin Cu(InGa)Se₂ layer at the CuInSe₂ surface has demonstrated increased $\text{V}{}_{\mathrm{<mtext>oc</mtext>}}$ with collection out to the CuInSe₂ band gap. A post-deposition treatment and contacting process for evaporated CdS/CdTe cells was developed and high efficiency cells were made. Several steps in the process, including a CdCl₂ coating, a 400 °C heat treatment, and a contact containing copper are critical. ZnTe films were deposited from an aqueous solution as a contact to CdTe.