1D/3D Alloying Induced Phase Transition in Light Absorbers for Highly Efficient Sb2Se3 Solar Cells

A simple binary inorganic antimony selenide (Sb2Se3) compound is attractive as a promising light absorber for low-cost and high-efficiency photovoltaics. The external quantum efficiencies of Sb2Se3 solar cells are now approaching the optical limit values, which are comparable with the traditional well-developed solar cells (such as Si, CuInGaSe2, CdTe, etc). However, the power conversion efficiency of the Sb2Se3 devices is constrained by the open-circuit voltage (V-OC) deficit, due to the intrinsic high resistivity and low element-doping efficiency in such one-dimensional (1D) crystals. Herein, a highly conductive, three-dimensional (3D) crystal-structure AgSbSe2 phase, formed by phase transition from low symmetry binary Sb2Se3, is introduced to control the doping density in the alloyed (Sb2Se3)(x)(AgSbSe2)(1-x) films utilizing configurational entropy. Guided by this alloying concept, 1D-3D (Sb2Se3)(x)(AgSbSe2)(1-x) alloy films with tunable doping densities are obtained. As a consequence, a noticeable improvement in V-OC by >18% is observed in solar cells based on the (Sb2Se3)(x)(AgSbSe2)(1-x) alloy absorber layer, compared with the reference cell with a pure Sb2Se3 absorber, leading to a high conversion efficiency of 7.8%. This alloying model provides a universal approach to control the photoelectrical properties for high-efficiency Sb2Se3-based solar cells.