Hybrid functional calculation of intrinsic defects in SbSeI

In recent years, the quasi-one-dimensional semiconductor Sb₂Se₃ has achieved a remarkable efficiency breakthrough over 10% [1] as a solar absorber. Due to their similar structures, SbSeI has also received significant attention. Particularly, the lone pair electrons in the valence band cause strong anti-bonding states formed by the hybridization of Sb 5s-Se 4p, as well as Sb 5s-I 5p orbitals, so the electronic properties can be more benign. However, its efficiency still remains at 4.1% [2]. Considering the crucial role of deep-level defects in limiting the photovoltaic efficiency of Sb₂Se₃, it is essential to investigate the defect properties of SbSeI to explore strategies for enhancing its photovoltaic performance. First-principles calculation reveals that SbSeI is, in fact, a semiconductor with high defect tolerance. Defects with high concentrations (10¹⁷-10¹⁸ cm^-3) in SbSeI are shallow (Se_I and I_Se), thus eliminating non-radiative recombination centers. However, these defects induce severe donor-acceptor compensation effect, resulting in carrier concentrations below 10¹¹ regardless of the growth condition and thus limiting the photovoltaic efficiency. To overcome the deficiency, we propose that p-type doping is favorable under Se-rich conditions, whereas under Sb-poor conditions, n-type doping is favored. Given the high defect tolerance of this material, it is expected that proper doping can significantly enhance the efficiency of photovoltaic devices.