Impact of in-situ Cd saturation MOCVD grown CdTe solar cells on As doping and V_OC

In-situ Cd-saturated growth of polycrystalline CdTe:As thin film was performed by metal organic chemical vapour deposition at a low temperature of 350 °C, to investigate the impact on As doping and device VOC. Device characterization showed conversion efficiency of ∼14%, and VOC of 772 mV, which is an improvement to the baseline device with CdTe:As absorber layer grown at 390 °C under non-saturated conditions. When the low temperature Cd-saturated growth was combined with chlorine heat treatment at a higher temperature of 440 °C (in contrast with the standard 420 °C) for 10 min, device efficiency improved to ∼17% with a high VOC of 877 mV. As a result, ∼100 mV boost in VOC from baseline is demonstrated with Cd-saturated CdTe:As device. Micro-photoluminescence and time-resolved photoluminescence measurements performed on these Cd-saturated CdTe:As devices confirmed that minority carrier lifetime significantly improved.</p

Achieving 21.4% efficient CdSeTe/CdTe solar cells using highly resistive intrinsic ZnO buffer layers

In this study, the use of intrinsic and highly insulating ZnO buffer layers to achieve high conversion efficiencies in CdSeTe/CdTe solar cells is reported. The buffer layers are deposited on commercial SnO2:F coated soda‐lime glass substrates and then fabricated into arsenic‐doped CdSeTe/CdTe devices using an absorber and back contact deposited by First Solar. The ZnO thickness is varied from 30 to 200 nm. The devices incorporating a 50 nm ZnO buffer layer achieved an efficiency of 21.23% without an anti‐reflection coating. An improved efficiency of 21.44% is obtained on a substrate with a multilayer anti‐reflection coating deposited prior to device fabrication. The highly efficient ZnO based devices are stable and do not develop anomalous J‐V behavior following environmental tests. High resolution microstructural analysis reveals the formation of a high‐quality ZnO/CdSeTe interface. Unusually, chlorine is not detected as a discrete layer at the interface, these observations point to a high‐quality interface. The extrapolation of Voc to 0 K indicates that interface recombination dominates, suggesting that further improvement is possible. Using device modeling, an attempt is made to understand how this type of device performs so well.</p