Enhanced Bifaciality Factor with Sb2Se3 Devices Modeling Cu2O Back Buffer

We have investigated bifacial Ge-incorporated Sb
2
Se
3
thin-film solar cells by modeling and simulating a back buffer layer including Cu
2
O to optimize the performance of bifacial devices. We proposed Ge-incorporated Sb
2
Se
3
absorber layers for bifacial devices, which were used as modeling input parameters after characterizing the absorber film. With extracted parameters (bandgap, 1.23 eV and the absorption coefficient, 3 × 10
⁵
cm
⁻¹
at 600 nm), we investigated the impact of various back buffer layers on bifacial device performance. The simulated device structure is ZnO:Al/i-ZnO/CdS/Ge-Sb
2
Se
3
/back buffer layer/TCO. First, the impact of conduction and valence band offsets was investigated, showing the significant dependence of device performance on valence band offset. To minimize the Schottky hole barrier at the back contact region, high back buffer doping concentration (1 × 10
¹⁵
cm
⁻³
or higher) is required to improve device performance, whereas low absorber doping concentration (<1 × 10
¹⁴
cm
⁻³
) enables higher efficiency due to the enlarged energy band bending. With a Cu
2
O back buffer layer, the best efficiency of front-side illumination is 19.7 %, Voc (744.4 mV), Jsc (40.14 mA/cm2), and FF (66.1 %) and that of the rear-side illumination is 13.0 %, Voc (724.5 mV), Jsc (31.6 mA/cm2), and FF (56.7 %). Consequently, the bifaciality factor is 66 %.