Doping in Efficient Polycrystalline CdSeTe Solar Cells via AsCl₃ Vapor Annealing

Doping in cadmium telluride (CdTe) thin-film solar cells is a critical step in producing highly efficient CdTe solar modules. To date, copper (Cu) ex-situ diffusion doping and group V in situ doping (such as arsenic, As) have been effectively used in manufacturing CdTe solar modules. However, Cu doping is prone to rapid degradation, whereas the low activation ratio of the dopants constrains group V in situ doping. Recently, ex-situ group V doping has been developed, showing an improved doping activation ratio through a solution process. In this study, we developed a vapor-based AsCl₃ doping method for diffusion doping of polycrystalline CdSeTe devices. AsCl₃ vapor annealing can promote the diffusion of As into the bulk CdSeTe through a surface chemical reaction between CdTe and AsCl₃. This approach has led to a long carrier lifetime of over 72 ns, V_oc of 850 mV, and power conversion efficiency of ∼18% with Au metal electrodes. The vapor-based ex situ group V doping approach offers an effective means to perform group V diffusion doping into the CdSeTe device.