Progress on defects of antimony chalcogenide thin film solar cells
As a kind of new photovoltaic materials,antimony chalcogenide(Sb2(SxSe1_x)3,0≤x≤1)thin films have been considered as a promising low-cost solar cell absorption layer material due to its excellent photoelectric performance and stability.Since the Nair group first applied Sb2S3 materials to sensitized structured solar cells in 2009,the preparation method and device structure of Sb2(SxSe1_x)3 have been continuously improved,and the photoelectric conversion efficiency(PCE)has been steadily improved to 10.75％.Despite the rapid progress,the device performance of antimony chalcogenide solar cells is still far from its theoretical limit.One of the key factors limiting the PCE of Sb2(SxSe1_x)3 thin film solar cells is defects.Generally,due to the influence of material properties and fabrication technology,it can be expected that there will be non-negligible defects in the absorption layer and interface of the Sb2(SxSe1_x)3 thin film solar cells.These defects can be formed internally or introduced externally,which have significant effects on the conductivity,carrier concentration,and recombination properties.According to the position of the defect transition level in the band gap,the influence of the defect on the properties of the semiconductor material can be divided into two aspects:(1)The defect near the band edge can contribute to the carrier concentration and adjust the Fermi level,thus determining the conduction type of the semiconductor(p-type or n-type).(2)Defects located deep in the band gap will limit the transmission of photogenerated carriers.Carriers trapped by defects deep in the band gap are extremely difficult to ionize at room temperature,leading to severe non-radiative recombination near the defects.Given the significant impact of defects on carrier transport properties and device performance,an in-depth understanding of defect properties in Sb2(SxSe1-x)3 materials is critical.The defect properties of Sb2(SxSe1-x)3 have been investigated using first-principles calculations based on density functional theory(DFT).Theoretical calculation shows that due to complex defects of Sb2(SxSe1-x)3,especially deep-level defects,Sb2(SxSe1_x)3 thin film solar cells have low carrier concentration and severe carrier recombination.Specifically,serious donor-acceptor compensation leads to low carrier concentration.Furthermore,high-concentration intrinsic defects have transition energy levels located deep in the band gap and can act as SRH recombination centers,further reducing carrier lifetime.Reasonable defect engineering of solar cells is considered to be an important strategy to improve the carrier concentration,reduce the Voc deficit and improve the device performance.The basic idea of defect engineering is to make use of favorable defects and effectively reduce or inhibit deep-level defects.In this review,we summarize the recent advances in the field of defects engineering of Sb2(SxSe1_x)3 thin film solar cells.On one hand,based on the comprehensive understanding of the material defect properties,rational use of defects or manufacturing defects control semiconductor material properties,such as doping.On the other hand,eliminating or inhibiting harmful defects,such as the improvement of preparation methods,optimization of precursors,control of film components,oxygen group element passivation,halogen element passivation,post-annealing technology,and the construction of ultra-thin interface layer,etc.Finally,the prospects for future research and development of Sb2(SxSe1-x)3 solar cells are discussed.
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