Exceeding 20% Efficiency with in situ Group V Doping in Polycrystalline CdTe Solar Cells

CdTe-based solar technology has achieved one of the lowest levelized costs of electricity among all energy sources as well as state-of-the-art field stability. Yet, there is still ample headroom to improve. For decades, mainstream technology has combined fast CdTe deposition with a CdCl₂ anneal and Cu doping. The resulting defect chemistry is strongly compensated and limits the useful hole density to ~10¹⁴ cm⁻³, creating a ceiling for fill factor, photovoltage and efficiency. In addition, Cu easily changes energy states and diffuses spatially, creating a risk of instabilities that must be managed with care. Here, we demonstrate a significant shift by doping polycrystalline CdSe_xTe_{1 − x} and CdTe films with As while removing Cu entirely from the solar cell. The absorber majority-carrier density is increased by orders of magnitude to 10¹⁶–10¹⁷ cm⁻³ without compromising the lifetime, and is coupled with a high photocurrent greater than 30 mA cm⁻². We demonstrate pathways for fast dopant incorporation in polycrystalline thin films, improved stability and 20.8% solar cell efficiency.