Reducing Parasitic Loss and Deep Defect Formation via Copper Doping Toward Highly Efficient Sb2Se3 Solar Cells

Abstract Antimony selenide (Sb 2 Se 3 ) has great potential as a light‐absorbing layer in thin‐film photovoltaics because of its excellent photoelectric properties and superior stability. Presently, high‐efficiency Sb 2 Se 3 solar cells use a heterojunction consisting of a p‐type Sb 2 Se 3 absorber and an n‐type CdS layer. The power conversion efficiency (PCE) of Sb 2 Se 3 solar cells is restricted by the low carrier concentration in the CdS layer, complex intrinsic deep defects of Sb 2 Se 3 , and unsuitable energy level band alignment in the junction. This paper presents a copper (Cu) doping strategy that achieves a synergistic doping effect, enabling controllable doping in both the n‐type CdS layer and p‐type Sb 2 Se 3 absorber. First, proper Cu doping significantly enhances the short‐wavelength transmittance of CdS films and increases their n‐type carrier concentration. The V bi in the CdS/Sb 2 Se 3 heterojunction improves from 521 to 751 mV. Second, a post‐annealing process is performed to facilitate Cu diffusion from the CdS layer to the Sb 2 Se 3 absorber. This approach successfully passivates intrinsic deep defect E2 and reduces the interfacial trap‐assisted nonradiative recombination losses. As a result, the Cu‐doped Sb 2 Se 3 /CdS solar cell presents a PCE of 10.23%, representing a 40% enhancement in PCE compared to the undoped CdS/Sb 2 Se 3 heterojunction device.