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 similar to 10(14) 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 CdSexTe1-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 10(16)-10(17) 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.