Back contact transparent conductive electrodes are essential components of semi-transparent perovskite solar cells, which are especially beneficial for tandem photovoltaics. In this Letter, we present a way to realize ultrathin metal layers in ITO-metal-ITO (IMI) electrode stacks, which are characterized by the superior infrared transmittance and electrical conductivity. The metal layers are deposited by the co-sputtering technique, which enables the realization of smooth metallic films, as thin as 5 nm. We applied the IMI electrodes to flexible high bandgap perovskite solar cells and demonstrated that the IMI electrodes based on the co-sputtered metals are outperforming the standard ITO electrodes in terms of cell performance, while maintaining similar transmission values. Furthermore, we show that the IMI electrodes are significantly more flexible than the standard ITO and, thus, are more suitable for flexible optoelectronic devices. The co-sputtering technique is compatible with the industrial production process. Overall, the co-sputtered IMI stack presented in this work paves the way for the commercial utilization of semi-transparent (visible or near-infrared range) photovoltaic devices, including high-efficiency tandem applications and window-integrated photovoltaics.

The synthesis and characterization of a family of indene-C₆₀ adducts obtained via Diels–Alder cycloaddition [4 + 2] are reported. The new C₆₀ derivatives include indenes with a variety of functional groups. These adducts show lowest unoccupied molecular orbital energy levels to be at the right position to consider these compounds as electron-transporting materials for planar heterojunction perovskite solar cells. Selected derivatives were applied into inverted (p–i–n configuration) perovskite device architectures, fabricated on flexible polymer substrates, with large active areas (1 cm²). The highest power conversion efficiency, reaching 13.61%, was obtained for the 6′-acetamido-1′,4′-dihydro-naphtho[2′,3′:1,2][5,6]fullerene-C₆₀ (NHAc-ICMA). Spectroscopic characterization was applied to visualize possible passivation effects of the perovskite’s surface induced by these adducts.