Investigation of electrically-active defects in Sb₂Se₃ thin-film solar cells with up to 5.91% efficiency via admittance spectroscopy

Admittance measurements were performed on Sb₂Se₃-based thin-film solar cells with energy conversion efficiencies from 3.85% to 5.91%. Three defects located at different energy levels above the valence band maximum (VBM) in the ranges of 0.3–0.4, 0.2–0.6 and 0.5–0.6 eV were identified for all cells and denoted D1, D2 and D3, respectively; the exact energy level of each defect within these ranges varied between cells. Correlations between the defect properties and the cell efficiencies were investigated and it was found that the activation energies of both D1 and D2 increased with decreasing efficiencies, the capture lifetime of holes increased with increasing efficiencies for both D1 and D2, and no obvious relationship with efficiency was found for D3. This indicated that D1 and D2 may play more important roles that affect the efficiencies in the measured samples. DC reverse bias-dependent admittance measurements enabled identification of D1 and D2 as bulk-type defects while D3 was identified as an interface or near-interface type defect. Finally, large parasitic series resistance and inductance effect, instead of defects, were considered to dominate the admittance spectra in the high frequency range (> 10⁵ Hz).