Impact of selenization temperature on the performance of sequentially evaporated CuInSe2 thin film solar cells

Abstract

In the present work, modified stacking of sequentially evaporated metallic precursors and two-step selenization was performed to examine the photovoltaic quality of the copper indium diselenide (CISe) thin films. The photovoltaic device performance as a function of selenization temperatures was investigated. Structural analysis showed that the chalcopyrite CISe thin films' crystallinity steadily improved as selenization temperatures increased from 450 to 550 °C. The grain size of the CISe thin films increased up to 1.0 μm with increasing selenization temperatures. The optical band gap energy fluctuated between 0.99 and 1.02 eV depending upon selenization temperatures. The uniform distribution of elements in the films' depth profile was investigated from secondary ion mass spectroscopy (SIMS). Open circuit voltage (Voc) increased from 258 to 543 mV upon increasing the selenization temperature due to enhanced crystal quality and concentration of sodium diffused through the soda-lime glass (SLG) substrate. A fabricated CISe solar cell attained 9.37% of best conversion efficiency at 550 °C of selenization temperature. These results demonstrate the selenization of evaporated metallic precursors at room temperature to synthesize good quality CISe based absorbers, which substantiate the viability of the proposed approach to obtain solar cells with high efficiency.