Perovskite CsPbIBr2 is attracting ever‐increasing attention for carbon‐based, all‐inorganic solar cells, owing to its well‐balanced band gap and stability features. However, significant interfacial recombination of charge carriers in solar cells fabricated with this active layer, which is intrinsically associated with the unwanted conduction band misalignment between CsPbIBr2 and the commonly used TiO2 electron transport layer, has limited power conversion efficiency (PCE) values. Herein, we demonstrate successful conduction band alignment engineering at the TiO2/CsPbIBr2 heterojunction by modifying TiO2 with CsBr clusters. Such modification triggers a beneficial increase in the conduction band minimum (CBM) of TiO2 from −4.00 to −3.81 eV and decreases the work function from 4.11 to 3.86 eV, thus promoting favorable band alignment at the heterojunction, suppressing recombination, and improving extraction and transport of charge carriers. As a result, the carbon‐based, all‐inorganic CsPbIBr2 solar cells exhibit over 20 % enhancement in average PCE. The champion device achieves a PCE of 10.71 %, a record among pure CsPbIBr2‐based cells, open‐circuit voltage of 1.261 V, and excellent stability.

The inferior crystallinity and phase stability of CsPbI2Br films have severely hindered the development of carbon-based, all-inorganic perovskite solar cells (PSCs). Herein, we demonstrate the preparation of CsPbI2Br films by the top-seeded solution growth (TSSG) technique. It is performed through spin-coating of CH3NH3Br (MABr) atop CsPbI2Br precursor film prior to annealing, during which perovskite seeds are generated atop it. These perovskite seeds not only serve as nuclei to regulate the growth of CsPbI2Br grains but also provide additional Br– anions to generate a thin Br-rich layer atop the final CsPbI2Br film. The former contributes to the formation of CsPbI2Br film with full coverage, larger grains, higher crystallinity, and fewer electronic defects, while the latter gives rise to residual compressive strain along the film and thus markedly boosts its phase stability. Consequently, the optimized carbon-based, all-inorganic PSC exhibits a much better efficiency of 14.84% coupled with favored storage and operational stability.

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl3–Cs4PbCl6 films. It is achieved by spin-coating of a certain dose of CH3NH3Cl/CsCl solution onto a CsI–PbBr2–dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl3–Cs4PbCl6 film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl3–Cs4PbCl6 film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310–420 nm, a high responsivity (R) peak value of 61.8 mA W–1, an exceptional specific detectivity (D*) maximum of 1.35 × 1012 Jones, and a particularly fast response speed of 2.1/5.3 μs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.

HIGHLIGHTS • A novel interface design of producing interfacial voids is proposed for CsPbIBr 2 perovskite solar cells (PSCs), which is free of any extra modification layer. • Interfacial voids improve absorption of CsPbIBr 2 film, reduce saturation current density, and enlarge built-in potential of the PSCs. • The PSC yields a superior efficiency of 10.20% with a record-high photovoltage of 1.338 V.

Carbon-based, all-inorganic perovskite solar cells (PSCs) have drawn enormous attention recently on account of their ungraded stability and reduced costs. However, their power conversion efficiencies (PCEs) still lag behind the ones with conventional architecture. Moreover, the high cost of FTO substrates and energy-consuming sintering process of TiO 2 electrontransporting layers should be further addressed. Herein, it is demonstrated that the FTO/TiO 2 substrates could be separated simply from degraded CsPbIBr 2 PSCs for fabricating the new ones again, which thus reduces the production costs of resulting PSCs and makes them renewable and sustainable. Meanwhile, the characterization results reveal that there are some residual CsPbIBr 2derived species on recycled FTO/TiO 2 substrates, which enable the upper CsPbIBr 2 films with suppressed halide phase separation and reduced defects, the diminished work function of TiO 2 layers from 4.13 to 3.89 eV, along with decreased conduction band minimum (CBM) difference of CsPbIBr 2 /TiO 2 interface from 0.51 to 0.36 eV. Consequently, the average PCE of CsPbIBr 2 PSCs is improved by 20%, from 6.51 ± 0.62% to 8.14 ± 0.63%, wherein the champion one yields the exceptional value of 9.12%. These findings provide an avenue for simultaneous performance enhancement and cost-saving of carbonbased, all-inorganic PSCs to promote their commercialization.