Sputter-deposited CdMgTe for rear contact to CdSeTe/CdTe solar cells

Abstract

CdTe-based photovoltaic device performance improvement is predominantly limited by open-circuit voltage. This work approaches the voltage deficit challenge through the incorporation of a cadmium magnesium telluride (CdMgTe) electron reflector layer at the back of 1.5- μm CdSeTe/CdTe absorbers to reduce back-surface recombination through a conduction band offset. A sputtered CdMgTe electron reflector layer permitted low fabrication temperatures and circumvented the intolerance of CdMgTe to thermal processing present in traditional close-space sublimation (CSS)-deposited CdMgTe devices. We demonstrate that sputtered CdMgTe simultaneously promotes the retention of chlorine passivation and magnesium which is not feasible with CSS fabrication. We also show the importance of the Cu and Te back contact order in CdMgTe devices. Through the optimization of the sputtered CdMgTe substrate temperature, doping, and back structure configuration, 1.5 μm CdSeTe/CdTe devices with a sputtered CdMgTe layer achieved an efficiency of 16.0%, significantly higher than with CSS CdMgTe, and demonstrated partial enactment of electron-reflector behavior. • Sputtered CdMgTe electron reflector solar cells achieve higher efficiencies than close-space sublimation-deposited. • Low temperatures of sputtered CdMgTe reduce magnesium diffusion and chlorine loss. • CdTe devices with CdMgTe electron reflectors require back contact optimization. • CdTe voltage improvement with CdMgTe limited by a partial negative back valence band offset.