Metal-halide perovskites have been widely investigated in the photovoltaic sector due to their promising optoelectronic properties and inexpensive fabrication techniques based on solution processing. Here we report the development of inorganic CsPbBr 3 -based photoanodes for direct photoelectrochemical oxygen evolution from aqueous electrolytes. We use a commercial thermal graphite sheet and a mesoporous carbon scaffold to encapsulate CsPbBr 3 as an inexpensive and efficient protection strategy. We achieve a record stability of 30 h in aqueous electrolyte under constant simulated solar illumination, with currents above 2 mA cm −2 at 1.23 V RHE . We further demonstrate the versatility of our approach by grafting a molecular Ir-based water oxidation catalyst on the electrolyte-facing surface of the sealing graphite sheet, which cathodically shifts the onset potential of the composite photoanode due to accelerated charge transfer. These results suggest an efficient route to develop stable halide perovskite based electrodes for photoelectrochemical solar fuel generation.

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Perovskite solar cells have gained increasing interest, especially after reaching performances which are comparable with mature silicon PV technologies. However, the perovskite crystalline structure CH 3 NH 3 PbI 3 is unstable in the presence of moisture, which leads to fast degradation under ambient conditions. The commercialisation of perovskite solar cells will only be achieved with the engineering of long term stable materials. We report a modified perovskite absorber layer obtained by adding methylammonium iodide (MAI) and tetrabutylammonium (TBA) iodide. The incorporation of TBA improves the film coverage, reducing the number of pinholes. X-ray diffraction analysis suggests that, in common with other mixed larger cation perovskites, two distinct phases coexist: a 3D perovskite material and a 2D layered material. The TBA containing perovskite films showed improved hydrophobicity, which contributed to significantly higher moisture stability. The cells maintained their original PCE after 45 days under ambient conditions without encapsulation. In comparison, the CH 3 NH 3 PbX 3 3D perovskite device lost more than 60% of its original efficiency over the same time.

Tin halide perovskites have recently emerged as promising materials for low bandgap solar cells. Much effort has been invested on controlling the limiting factors responsible for poor device efficiencies, namely...

We show that pristine thin films made of tin halide perovskite have external photoluminescence quantum yield comparable to that of lead halide perovskite, i.e., the material in use to prepare state-of-the-art perovskite solar cells.

Mesoporous carbon solar cells were prepared by infiltrating the porous substrate with inorganic CsPbBr3 solution. The films were post-annealed at different temperatures; post-annealing at 400 °C strongly enhances the open circuit voltage (1.44 V) and cell efficiency (8.2%).

The instability of halide perovskites toward moisture is one of the main challenges in the field that needs to be overcome to successfully integrate these materials in commercially viable technologies. One of the most popular ways to ensure device stability is to form 2D/3D interfaces by using bulky organic molecules on top of the 3D perovskite thin film. Despite its promise, it is unclear whether this approach is able to avoid 3D bulk degradation under accelerated aging conditions, i.e., thermal stress and light soaking. In this regard, it is crucial to know whether the interface is structurally and electronically stable or not. In this work, we use the bulky phenethylammonium cation (PEA+) to form 2D layers on top of 3D single- and triple-cation halide perovskite films. The dynamical change of the 2D/3D interface is monitored under thermal stress and light soaking by in situ photoluminescence. We find that under pristine conditions the large organic cation diffuses only in 3D perovskite thin films of poor structural stability, i.e., single-cation MAPbI3. The same diffusion and a dynamical change of the crystalline structure of the 2D/3D interface are observed even on high-quality 3D films, i.e., triple-cation MAFACsPbI3, upon thermal stress at 85 °C and light soaking. Importantly, under such conditions, the resistance of the thin film to moisture is lost.

Bandgap tuning is a crucial characteristic of metal-halide perovskites, with benchmark lead-iodide compounds having a bandgap of 1.6 eV. To increase the bandgap up to 2.0 eV, a straightforward strategy is to partially substitute iodide with bromide in so-called mixed-halide lead perovskites. Such compounds are prone, however, to light-induced halide segregation resulting in bandgap instability, which limits their application in tandem solar cells and a variety of optoelectronic devices. Crystallinity improvement and surface passivation strategies can effectively slow down, but not completely stop, such light-induced instability. Here we identify the defects and the intragap electronic states that trigger the material transformation and bandgap shift. Based on such knowledge, we engineer the perovskite band edge energetics by replacing lead with tin and radically deactivate the photoactivity of such defects. This leads to metal halide perovskites with a photostable bandgap over a wide spectral range and associated solar cells with photostable open circuit voltages.