Highly efficient bifacial CsPbIBr2 solar cells with a TeO2/Ag transparent electrode and unsymmetrical carrier transport behavior

Abstract

Bright red CsPbIBr₂ films possess intrinsic semitransparent features, which make them promising materials for smart photovoltaic windows, power plants, curtain walls, top cells for tandem solar cells, and bifacial photovoltaics. In this work, bifacial CsPbIBr₂ perovskite solar cells (PSCs) have been fabricated by adopting an ultrathin silver (Ag) film transparent anode and a tellurium oxide (TeO₂) optical modifying layer. The results showed that the transmittance of the TeO₂ (40 nm)/Ag (11 nm) transparent top anode matched well with the light absorption range of the CsPbIBr₂ film, and the resulting bifacial PSCs exhibited PCEs of 8.04% and 5.32% when illuminated from the FTO and Ag sides, respectively. By introducing cesium iodide-treated CsPbIBr₂ layers, the PSCs achieved superior PCEs of 8.46% (FTO side) and 6.40% (Ag side) with a bifacial factor of 75.65%, which is the best performance of bifacial CsPbIBr₂ PSCs reported to date. Interestingly, an identical cell showed a significantly higher fill factor, more efficient carrier transport, and better efficiency and stability when illuminated from the Ag side than from the FTO side, a phenomenon strongly related to the parasitic absorption of the spiro-OMeTAD layer below 420 nm. Consequently, we have found a route similar to “shooting fish in a barrel” to enhance the carrier transport, suppress the carrier recombination, and improve the stability of bifacial semitransparent CsPbIBr₂ PSCs: turning the Ag side towards the sun.