Efficiency Enhancement of Bifacial Sb₂Se₃ Photovoltaic Devices with Cu₂O Back Buffer: A Modeling Study

Thin-film solar cells based on an Antimony Selenide (Sb₂Se₃) absorber layer have been emerging as third-generation photovoltaic devices with promising properties. A Sb₂Se₃ absorber has 1.1 eV bandgap, a high absorption coefficient at visible light (&gt;10⁵ cm⁻¹), good carrier mobility (&lt;15 cm²/Vs), long carrier lifetime (&lt;67 ns), and simple binary compound with high vapor pressure and low melting point (550 °C).<br/>Due to the versatility of Sb₂Se₃ thin-films, Sb₂Se₃ has been studied by varying compositions and concentrations of incorporated elements for various applications. In particular, Ge-incorporated Sb₂Se₃ thin-films (hereafter, Ge- Sb₂Se₃) have been reported as a good polycrystalline absorber candidate with Ge concentration &lt;15 %.<br/>To further improve the efficiency of polycrystalline Sb₂Se₃ devices, both front and rear-side illumination could be captured by utilizing the bifacial device configuration of Sb₂Se₃ devices. However, developing bifacial devices has stagnated in thin-film photovoltaic technologies due to the short carrier lifetime (&lt;100 nS) as compared to polysilicon counterparts. For instance, the record efficiency of rear-side illumination is reported as 9.2 % for CIGS, 8.0 % for CdTe, and 9.0 % for Kesterite solar cells, respectively. Designing a bifacial photovoltaic structure has been studied by several research groups and recently, a few studies of thin-film devices with a thin absorber (&lt;2 um) such as CIGS, CdTe, and Kesterite have been reported. By carefully selecting a transparent back buffer layer coupled with a transparent conducting back contact, a bifacial device configuration needs to be optimized in thickness and doping concentration to maximize a bifaciality factor, which is the ratio of rear-to-front efficiency to the same irradiation.<br/>In this contribution, we have theoretically studied bifacial Ge Sb₂Se₃ devices after fabricating Ge Sb₂Se₃absorber thin-films, followed by characterizing the optical properties. The optical properties of a Ge- Sb₂Se₃ absorber layer were used as input parameters for modeling and numerical simulation of the bifacial device configuration. For our analytical simulation, we have used in-house MATLAB modeling suites that have been developed in our group. We have proposed new bifacial devices to improve the overall device performance and optimized developed device models with various parameters. With a Cu₂O 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 %). For the rear-side illumination, the performance is 13.0 %, Voc (724.5 mV), Jsc (31.6 mA/cm2), and FF (56.7 %). Consequently, the bifaciality factor is 66 %.