Application of Bifacial Semitransparent CuInSe₂ Absorber to the Bottom Cell in Bifacial Semitransparent Perovskite/CuInSe₂ Tandem Solar Cell for Albedo Environment

Abstract Although various types of bifacial solar cells exist, few studies have been conducted on bifacial semitransparent CuInSe₂ solar cells (BS‐CISe SCs) despite the attractive potential in power generation from both sides in an albedo environment. The optimized BS‐CISe SCs with 300 and 800 nm‐thick absorber via a streamlined single‐stage co‐evaporation process exhibit a power conversion efficiency (PCE) of 6.32% and 10.6%, respectively. When double‐sided total 2.0 sun illumination is assumed in an albedo environment, the bifacial power generation densities (BPGD) of them increases to 9.41% and 13.9%. Four‐terminal bifacial semitransparent tandem solar cells (4T‐BST SCs) are fabricated to increase the BPGD by mechanically stacking a BS‐perovskite (PVK) top cell on top of a BS‐CISe bottom cell with the 300 and 800 nm‐thick absorber layers. When summed up, the best top and bottom cell PCEs of the 4T‐BST SC with 300 and 800 nm‐thick BS‐CISe SC are 18.8% and 21.1%, respectively. However, the practical BPGD values of the 4T‐BST SC under total 2 sun illumination are interestingly 23.4% and 24.4%, respectively. This is because the BS‐CISe bottom cell's thickness affects how much rear‐side illumination is transmitted to the BS‐PVK top cell, increasing its current density and BPGD.