Radiative Efficiency and Charge‐Carrier Lifetimes and Diffusion Length in Polycrystalline CdSeTe Heterostructures

CdTe‐based photovoltaics is a rapidly developing energy technology with one of the lowest levelized costs of electricity. But nonradiative Shockley–Read–Hall (SRH) recombination limits the efficiency of CdTe solar cells. Partial mitigation of bulk and grain‐boundary SRH recombination was achieved by alloying CdTe with Se, and CdSe x Te 1− x absorbers are used in high‐efficiency solar cells. Recently, interface recombination was significantly reduced with alumina passivation, but other properties of Al 2 O 3 /CdSe x Te 1− x /Al 2 O 3 heterostructures have not yet been investigated. Herein, further progress in understanding and developing polycrystalline heterostructures with x = 0.2 is reported. It is shown that external photoluminescence quantum yield is increased to 0.2%, quasi‐Fermi‐level splitting to 950 mV, minority carrier lifetimes to 750 ns, and mobility to 100 cm 2 Vs −1 . Such polycrystalline CdSe x Te 1− x electronic characteristics match or exceed CdTe single‐crystal properties. The resulting charge‐carrier diffusion length of ≈14 μm is several times greater than the absorber thickness in test structures and in typical CdTe solar cells. Herein, with passivation and absorbers, polycrystalline CdSeTe solar cell open‐circuit voltage is increased from the current 76% of the Shockley–Queisser limit to 82%, or close to 1 V is reported.