An efficient TeO2/Ag transparent top electrode for 20%-efficiency bifacial perovskite solar cells with a bifaciality factor exceeding 80%

Bifacial photovoltaic technology has been established as an effective strategy for increasing electric power generation while reducing the area-related costs of silicon solar cells. For third-generation solar cells of organolead halide perovskites, the monofacial power conversion efficiency (PCE) has exceeded 23%. Therefore, the development of efficient bifacial cells is expected, but the top transparent electrode is a crucial obstacle that must be overcome. In this work, ultrathin silver (Ag) film was selected as the top transparent electrode and, particularly, a tellurium oxide (TeO2) optical coupling layer was adopted to enhance the transmittance of the Ag film in the visible light region, which markedly increased the light absorption of devices. Compared with PSCs with a pure Ag electrode, the device with a TeO2 (40 nm)/Ag (11 nm) top electrode showed significantly enhanced bifacial short-circuit current-density and bifacial PCEs of 18.86% (illuminated from the ITO electrode) and 15.12% (illuminated from the Ag electrode). Consequently, in addition to its role as a transmittance enhancement layer, TeO2 acted as a back reflector when the device was illuminated from the ITO side. Furthermore, a previously proposed phenylethylammonium iodide treatment method was adopted to improve charge transport at the perovskite/fullerene interface. Remarkably, the device achieved champion bifacial PCEs of 20.96% (ITO side) and 17.36% (Ag side), a bifaciality factor of 82.82%, and a steady PCE output and good reproducibility. The large-area device (1 cm2) achieved bifacial PCEs of 12.42% (ITO side) and 10.55% (Ag side), with better performance predicted by simulations. Therefore, the TeO2/Ag films are promising transparent electrodes for fabricating cost-effective bifacial PSCs.