The engineering of the electron transport layer (ETL)/light absorber interface is explored in perovskite solar cells. Single‐crystalline TiO2 nanorod (NR) arrays are used as ETL and methylammonium lead iodide (MAPI) as light absorber. A dual ETL surface modification is investigated, namely by a TiCl4 treatment combined with a subsequent PC61BM monolayer deposition, and the effects on the device photovoltaic performance were evaluated with respect to single modifications. Under optimized conditions, for the combined treatment synergistic effects are observed that lead to remarkable enhancements in cell efficiency, from 14.2% to 19.5%, and to suppression of hysteresis. The devices show JSC, VOC, and fill factor as high as 23.2 mA cm−2, 1.1 V, and 77%, respectively. These results are ascribed to a more efficient charge transfer across the ETL/perovskite interface, which originates from the passivation of defects and trap states at the ETL surface. To the best of our knowledge, this is the highest cell performance ever reported for TiO2 NR‐based solar cells fabricated with conventional MAPI light absorber. Perspective wise, this ETL surface functionalization approach combined with more recently developed and better performing light absorbers, such as mixed cation/anion hybrid perovskite materials, is expected to provide further performance enhancements.

We investigate the co-catalytic activity of PtCu alloy nanoparticles for photocatalytic H2 evolution from methanol-water solutions. To produce the photocatalysts, a few nm-thick Pt-Cu bilayers are deposited on anodic TiO2 nanocavity arrays and converted by solid state dewetting, i.e. a suitable thermal treatment, into bimetallic PtCu nanoparticles. XRD and XPS results prove the formation of PtCu nanoalloys that carry a shell of surface oxides. XANES data support Pt and Cu alloying and indicate the presence of lattice disorder in the PtCu nanoparticles. The PtCu co-catalyst on TiO2 shows a synergistic activity enhancement and a significantly higher activity towards photocatalytic H2 evolution than Pt-or Cu-TiO2. We propose the enhanced activity to be due to Pt-Cu electronic interactions, where Cu increases the electron density on Pt favoring a more efficient electron transfer for H2 evolution. In addition, Cu can further promote the photo-activity by providing additional surface catalytic sites for hydrogen recombination. Remarkably, when increasing the methanol concentration up to 50 vol% in the reaction phase, we observe for PtCu-TiO2 a steeper activity increase compared to Pt-TiO2. A further increase in methanol concentration (up to 80 vol%) causes for Pt-TiO2 a clear activity decay, while PtCu-TiO2 still maintains a high level of activity. This suggests an improved robustness of PtCu nanoalloys against poisoning from methanol oxidation products such as CO.

We examine comparatively the performance of sputtered TiO2 rutile and anatase thin films as an electron transport layer (ETL) in MAPbI3‐based perovskite solar cells. Both anatase and rutile TiO2 ETLs are deposited (on fluorine‐doped tin oxide [FTO] substrates) by magnetron sputtering in the form of nanocrystalline thin films. We systematically investigate the role of crystallographic phase composition of TiO2 ETLs on the photovoltaic performance of perovskite solar cells. The champion power conversion efficiencies (PCEs) of 18.4% and 17.7% under reverse scan mode are obtained for perovskite solar cells based on TiO2 anatase and TiO2 rutile ETL, respectively. The results show that the magnetron sputtering deposited ETLs differ from each other only in their phase composition while the overall performance of the devices is not greatly affected by the crystallographic phase of the TiO2 ETLs. Our results point to an important fact that for a proper and reliable comparison between the performance of TiO2 anatase and rutile ETLs, it is crucial to investigate films of similar morphology and structure that are synthesize under similar conditions.