Plasma-induced damage-free bifacial perovskite solar cells for photovoltaic windows

Bifacial perovskite solar cells (B-PSCs) have emerged as promising candidates for photovoltaic windows in smart buildings and automobiles owing to their ability to harvest light from both sides. However, direct sputtering of transparent conductive oxides onto a soft perovskite absorber layer (PAL) poses challenges due to plasma-induced damage. In this study, we developed a low-damage Ga/Ti co-doped In₂O₃ (IGTO) anode, combined with a thermally evaporated MoO_x buffer layer, to mitigate PAL degradation. Compared to a conventional sputtered indium–tin oxide anode, which severely affects the PAL and device performance, the IGTO/MoO_x structure enables the fabrication of stable B-PSCs even with ultrathin PAL layers without any passivation layer. As the PAL thickness decreases from 600 to 50 nm, the power conversion efficiency (Transmittance) of the IGTO/MoO_x-based B-PSCs varies from 17.50 % (0.34 % transmittance) to 5.08 % (46.4 % transmittance), highlighting the impact of light absorption. Similarly, the efficiency of Au-based opaque PSCs decreases from 17.92 % to 7.11 %, further demonstrating the role of low-damage sputtering in minimizing PAL degradation. Under optimized conditions (IGTO: 400 nm, MoO_x: 15 nm), the bifacial device achieves PCEs of 18.34 % (with a white sheet) and 20.60 % with standard sunlight and indoor lighting (1000 lx), respectively, in the front-side illumination mode. Rear-side illumination results in PCEs of 16.82 % (with a white sheet, outdoors) and 18.34 % (indoors). These results establish low-damage sputtering as a key strategy for achieving high-performance commercially viable B-PSCs and provide insights into the design of top cells for multijunction solar technologies.