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We present that atomic layer deposition (ALD) of TiO 2 thin layer on SnO 2 electron transport layer (ETL) could simultaneously boost the crystallization control of CsPbIBr 2 absorber film and band alignment of all-inorganic perovskite solar cell (PSC). The former awards the desired CsPbIBr 2 film characterized by high crystallinity, weak halide phase separation, as well as extremely uniform- and large-sized grains. And, the latter brings a cascade pathway for electron extraction and transport in the cell. Such combined morphology tailoring and interface engineering are extremely beneficial to suppress both bulk recombination and interfacial recombination of charge carrier. As a result, the cell' efficiency can be boosted from 6.11% to 9.31%, which is beyond all the pure CsPbIBr 2 -based PSCs reported to date. Therefore, our works highlight the dual functions of ALD-processed TiO 2 interfacial layer in processing high-performance all-inorganic PSC. Atomic layer deposition (ALD) of TiO 2 thin layer on SnO 2 electron transport layer could simultaneously boost the crystallization control of CsPbIBr 2 absorber film and band alignment of all-inorganic perovskite solar cell. Thus, the cell efficiency can be boosted from 6.11% to the record-high value of 9.31%. Image 1 • ALD-processed TiO 2 on SnO 2 ETL triggers dual functions of crystallization control and band alignment in CsPbIBr 2 PSC. • Crystallization control enables high crystallinity, weak phase separation, and uniformly large-sized grains in CsPbIBr 2 film. • Band alignment facilitates a cascade pathway for electron extraction and transport. • The dual functions of TiO 2 thin layer boost efficiency of pure CsPbIBr 2 -based cell to the record-high value of 9.31%. [ABSTRACT FROM AUTHOR]

Highlights: A novel interface design of producing interfacial voids is proposed for CsPbIBr2 perovskite solar cells (PSCs), which is free of any extra modification layer. Interfacial voids improve absorption of CsPbIBr2 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. A novel interface design is proposed for carbon-based, all-inorganic CsPbIBr2 perovskite solar cells (PSCs) by introducing interfacial voids between TiO2 electron transport layer and CsPbIBr2 absorber. Compared with the general interfacial engineering strategies, this design exempts any extra modification layer in final PSC. More importantly, the interfacial voids produced by thermal decomposition of 2-phenylethylammonium iodide trigger three beneficial effects. First, they promote the light scattering in CsPbIBr2 film and thereby boost absorption ability of the resulting CsPbIBr2 PSCs. Second, they suppress recombination of charge carriers and thus reduce dark saturation current density (J0) of the PSCs. Third, interfacial voids enlarge built-in potential (Vbi) of the PSCs, awarding increased driving force for dissociating photo-generated charge carriers. Consequently, the PSC yields the optimized efficiency of 10.20% coupled with an open-circuit voltage (Voc) of 1.338 V. The Voc achieved herein represents the best value among CsPbIBr2 PSCs reported earlier. Meanwhile, the non-encapsulated PSCs exhibit an excellent stability against light, thermal, and humidity stresses, since it remains ~ 97% or ~ 94% of its initial efficiency after being heated at 85 °C for 12 h or stored in ambient atmosphere with relative humidity of 30–40% for 60 days, respectively. [ABSTRACT FROM AUTHOR]