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Bandgap‐tunable mixed‐halide perovskite materials have attracted considerable interest because of their indispensability as top counterparts in tandem solar cells. However, the soft and disordered lattice always suffers from severe phase segregation under illumination, which is particularly susceptible to residual lattice strain. Herein, we report a strain regulation strategy by using alkenamides terminated Ti3C2Tx MXenes as an additive into perovskite precursor. Apart from the role of a template for grain growth to obtain high‐quality films, the stretchable alkyl chain promotes lattice shrinkage or expansion to form an elastic grain boundary to eliminate the spatially distributed stain and shut down ion migration channels. As a result, the all‐inorganic perovskite solar cells based on CsPbIBr2 and CsPbI2Br halides achieve prolonged device stability under harsh conditions and the best power conversion efficiencies up to 11.06% and 14.30%, respectively. An elastic interface is fabricated to release residual lattice compressive and tensile strain of mixed‐halide inorganic CsPbIB2 perovskite film by using a stretchable alkenamides terminated Ti3C2Tx MXene as an additive, universally healing the defective lattices to suppress the nonradiative recombination and improving the efficiency and stability of wide‐bandgap perovskite solar cells.

Inorganic mixed‐halide CsPbX3‐based perovskite solar cells (PeSCs) are emerging as one of the most promising types of PeSCs on account of their thermostability compared to organic–inorganic hybrid counterparts. However, dissatisfactory device performance and high processing temperature impede their development for viable applications. Herein, a facile route is presented for tuning the energy levels and electrical properties of sol–gel‐derived ZnO electron transport material (ETM) via the doping of a classical alkali metal carbonate Cs2CO3. Compared to bare ZnO, Cs2CO3‐doped ZnO possesses more favorable interface energetics in contact with the CsPbI2Br perovskite layer, which can reduce the ohmic loss to a negligible level. The optimized PeSCs achieve an improved open‐circuit voltage of 1.28 V, together with an increase in fill factor and short‐circuit current. The optimized power conversion efficiencies of 16.42% and 14.82% are realized on rigid glass substrate and flexible plastic substrate, respectively. A high thermostability can be simultaneously obtained via defect passivation at the Cs2CO3‐doped ZnO/CsPbI2Br interface, and 81% of the initial efficiency is retained after aging for 200 h at 85 °C. An all‐inorganic mixed‐halide perovskite solar cell with a power conversion efficiency of 16.42% is realized by using a Cs2CO3‐doped ZnO electron transport layer, which ascribes to the interfacial energy level tuning for reducing ohmic loss at the contact and enlarging the built‐in potential. A high thermostability is simultaneously obtained via surface defect passivation for improving the CsPbI2Br film against phase transformation.

Cesium‐based all‐inorganic wide‐bandgap perovskite solar cells (AIWPSCs) have been demonstrated with exceptional optoelectronic properties such as intrinsic optical wide‐bandgap and high thermal stability, which make them suitable candidates for the front sub‐cells of tandem solar cells (TSCs). Passivation of perovskite surface and interface is a matter of common interest in this community since all‐inorganic perovskites always suffer from non‐ideal crystallization such as phase impurity, high defect density, and non‐uniform morphology. Despite these shortcomings, numerous efforts have been devoted in recent years to pursuing high‐performance AIWPSCs, which exhibit an abruptly increased power conversion efficiency (PCE) from 2.9% to over 21.0%. In view of not having a thorough summary about the advancements on AIWPSCs, herein, a comprehensive review is given to highlight the recent device performance progress of AIWPSC, particularly focusing on the strategies to passivate the defects of all‐inorganic perovskite, namely, additive engineering, solvent engineering, interface modification, and the exploration of new charge transport materials (CTMs) for improving the phase stability and PCE of AIWPSCs. Finally, a conclusive outlook on AIWPSCs will be given to provide our perspectives aiming to inspire the further development of AIWPSCs. The progress in the device performance of all‐inorganic wide‐bandgap perovskite solar cells (AIWPSCs) with respect to their photovoltaic parameters (VOC, JSC, FF, and PCE), and optimization strategies (additive engineering, solvent engineering, and interface engineering) is comprehensively reviewed. This work consolidates the recent developments of AIWPSCs aiming to provide new inspirations for further advancements in AIWPSCs.

HighlightsA 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.

All-inorganic perovskites, adopting cesium (Cs + ) cation to completely replace the organic component of A-sites of hybrid organic–inorganic halide perovskites, have attracted much attention owing to the excellent thermal stability. However, all-inorganic iodine-based perovskites generally exhibit poor phase stability in ambient conditions. Herein, we propose an efficient strategy to introduce antimony (Sb 3+ ) into the crystalline lattices of CsPbI 2 Br perovskite, which can effectively regulate the growth of perovskite crystals to obtain a more stable perovskite phase. Due to the much smaller ionic radius and lower electronegativity of trivalent Sb 3+ than those of Pb 2+ , the Sb 3+ doping can decrease surface defects and suppress charge recombination, resulting in longer carrier lifetime and negligible hysteresis. As a result, the all-inorganic perovskite solar cells (PSCs) based on 0.25% Sb 3+ doped CsPbI 2 Br light absorber and screen-printable nanocarbon counter electrode achieved a power conversion efficiency of 11.06%, which is 16% higher than that of the control devices without Sb 3+ doping. Moreover, the Sb 3+ doped all-inorganic PSCs also exhibited greatly improved endurance against heat and moisture. Due to the use of low-cost and easy-to-process nanocarbon counter electrodes, the manufacturing process of the all-inorganic PSCs is very convenient and highly repeatable, and the manufacturing cost can be greatly reduced. This work offers a promising approach to constructing high-stability all-inorganic PSCs by introducing appropriate lattice doping.

The crystal distortion such as lattice strain and defect located at the surfaces and grain boundaries induced by soft perovskite lattice highly determines the charge extraction‐transfer dynamics and recombination to cause an inferior efficiency of perovskite solar cells (PSCs). Herein, the authors propose a strategy to significantly reduce the superficial lattice tensile strain by means of incorporating an inorganic 2D Cl‐terminated Ti3C2 (Ti3C2Clx) MXene into the bulk and surface of CsPbBr3 film. Arising from the strong interaction between Cl atoms in Ti3C2Clx and the under‐coordinated Pb2+ in CsPbBr3 lattice, the expanded perovskite lattice is compressed and confined to act as a lattice “tape”, in which the PbCl bond plays a role of “glue” and the 2D Ti3C2 immobilizes the lattice. Finally, the defective surface is healed and a champion efficiency as high as 11.08% with an ultrahigh open‐circuit voltage up to 1.702 V is achieved on the best all‐inorganic CsPbBr3 PSC, which is so far the highest efficiency record for this kind of PSCs. Furthermore, the unencapsulated device demonstrates nearly unchanged performance under 80% relative humidity over 100 days and 85 °C over 30 days. Arising from the formation of strong PbCl bonding, chlorine terminated Ti3C2Clx MXenes are used as lattice “tape” to reduce the defects and release tensile strain located at interfaces and grain boundaries of CsPbBr3 perovskite film, achieving a champion efficiency up to 11.08% with an ultrahigh voltage of 1.702 V for CsPbBr3 perovskite solar cells.

Over the past two decades, organic–inorganic hybrid perovskites have shown continuous improvement in photovoltaic performance. However, thermal instability and the presence of lead are still issues, and research efforts are aimed at combatting this. In addition, high power conversion efficiency remains the primary goal. Cesium-based inorganic perovskite compounds have emerged with more stable performance against varying environmental conditions. In this study, a low-lead cesium-based all-inorganic mixed-halide perovskite solar cell (IMH-PSC) was designed using the SCAPS-1D simulator. To enhance the photon absorption, a double-absorber-layer perovskite solar cell (DAL-PSC) architecture was considered for absorption of the high-/low-energy photons in the top/bottom perovskite layer (TPL/BPL), respectively. The IMH perovskites used in the DAL-PSC included CsPb0.625Zn0.375I2Br, CsPb0.625Zn0.375I2Cl, and CsPb0.625Zn0.375IBr2. After the performance of the DAL-IMH-PSC was analysed using SCAPS, machine learning models were trained and tested to predict the photovoltaic (PV) parameters and to determine the impact of input parameters such as absorber layer thickness and defect density on the PV performance of the DAL-IMH-PSC design. Using SCAPS-1D, a dataset of 29,400 combinations was extracted with varied input parameters: TPL thickness from 0.05 μm to 1 μm, BPL thickness from 0.05 μm to 0.5 μm, and TPL/BPL defect density from 1 × 1012 cm−3 to 1 × 1018 cm−3. The DAL-IMH-PSC layered as fluorine-doped tin oxide (FTO)/TiO2/CsPb0.625Zn0.375I2Cl/CsPb0.625Zn0.375IBr2/Spiro-MeOTAD/back electrode delivered the highest power conversion efficiency (PCE), at 30.36%. The random forest and extreme gradient boosting algorithms showed the best prediction performance. In addition, features of importance were identified with the help of SHAP (SHapley Additive exPlanations) plots, which showed the inverse dependence of bottom defect density on PCE.

Active oxygen highly affects the efficiency and stability of perovskite solar cells (PSCs) owing to the capacity to either passivate defects or decompose perovskite lattice. To better understand the in‐depth interaction, we demonstrate for the first time that photooxidation mechanism in all‐inorganic perovskite film dominates the phase deterioration kinetics by forming superoxide species in the presence of light and oxygen, which is significantly different from that in organic‒inorganic hybrid and even tin‐based perovskites. In all‐inorganic perovskites, the superoxide species prefer to oxidize longer and weaker Pb‒I bond to PbO and I2, leaving the much stable CsPbBr3 phase. From this chemical proof‐of‐concept, we employ an organic bioactive factor, Tanshinone IIA, as a superoxide sweeper to enhance the environmental tolerance of inorganic perovskite, serving as a “skincare” agent for anti‐aging organisms. Combined with another key point on healing defective lattice, the best carbon‐based all‐inorganic CsPbI2Br solar cell delivers an efficiency as high as 15.12% and superior stability against oxygen, light, humidity, and heat attacks. This method is also applicable to enhance the efficiency of p‒i‒n inverted (Cs0.05MA0.05FA0.9)Pb(I0.93Br0.07)3 cell to 23.46%. These findings not only help us understand the perovskite decomposition mechanisms in depth but also provide a potential strategy for advanced PSC platforms. We reveal the decomposition mechanism of all‐inorganic mixed‐halide perovskite under light/O2 exposure, which suffers from a photooxidation process by oxidizing Pb‒I bond to PbO and I2, leaving CsPbBr3 phase. A bioinspired “skincare” strategy by adding Tanshinone IIA into perovskite film is proposed to passivate defects and sweep superoxide species, remarkably enhancing the stability and efficiency of PSC.

This study thoroughly investigates the effects of different solvent engineering strategies on the structure and properties of SnO 2 electron transport layers (ETLs) and evaluates their performance-enhancing effects on carbon-based all-inorganic CsPbIBr 2 perovskite solar cells (PSCs). By comparing the SnO 2 ETLs prepared with ethanol (ET-SnO 2 ) and isopropanol (IPA-SnO 2 ) solvents and constructing corresponding CsPbIBr 2 PSCs devices, we comprehensively analysed the structure, morphology, wettability, light transmittance and electronic transport properties of the SnO 2 ETLs using characterization methods such as XRD, SEM, contact angle measurement, transmission spectroscopy, steady-state fluorescence spectroscopy and electrochemical impedance spectroscopy. Combined with the J-V characteristics of the device, we revealed the mechanism of the effect of solvent engineering on the performance of PSCs. The results showed that IPA-SnO 2 exhibited better performance with lower contact angle and higher compactness, which is conducive to electron transport and reduces interfacial defects. IPA-SnO 2 also promoted the growth of CsPbIBr 2 crystals, forming larger and denser crystal structures and reducing pinhole defects. In addition, IPA-SnO 2 improves the light transmittance of the FTO substrate and the light absorption of the CsPbIBr 2 film, thereby increasing the light trapping efficiency. Finally, the IPA-SnO 2 -based PSCs achieved a PCE of 5.95%, an improvement of 25% compared to ET-SnO 2 , demonstrating good application prospects. This study provides an important experimental basis for optimizing the preparation process of SnO 2 ETL and improving the performance of carbon-based CsPbIBr 2 PSCs. Graphical Abstract Highlights Investigation of the effects of different solvent engineering strategies (ethanol and isopropanol) on the structure and properties of SnO 2 ETLs. Fabrication and characterization of carbon-based CsPbIBr 2 PSCs with SnO 2 ETLs prepared using different solvents. Analysis of the effect of solvent engineering on the performance of PSCs, including device structure, energy level arrangement and material properties.

All-inorganic perovskite solar cells suffer from low performance due to unsatisfactory carrier transport and light harvesting efficiency. Semiconductor nanopillar arrays can reduce light reflection loss and suppress exciton recombination dynamics in optoelectronic devices. In all-inorganic perovskite solar cells, few studies employing TiO 2 nanopillar arrays (TiO 2 NaPAs) have been reported to improve the device performance. Herein, well-arranged TiO 2 NaPAs are chosen to enhance the interfacial contact between perovskite and electron transporting layers for improving the carrier transport. Notably, TiO 2 NaPAs can be directly fabricated on rigid/flexible substrates at roughly room temperature by unique glancing angle deposition, which is more available than high-temperature hydrothermal/solvothermal methods. By embedding TiO 2 NaPAs into chemical processable CsPbI 2 Br layers, continuous and intimate films are readily formed, guaranteeing large physical contact for facilitating more effective electron injection and charge separation. The vertically grown TiO 2 NaPAs also provide a straightforward electron transporting path to electrodes. In addition, TiO 2 NaPAs can guide the incident light and enhance the light-harvesting ability of CsPbI 2 Br films. As a result, the solar cell with TiO 2 NaPAs displays a power conversion efficiency of 11.35% higher than planar control of 10.04%, and exhibits better long-term thermal stability. This strategy provides an opportunity by constructing direct interfacial regulation towards the performance improvement of inorganic perovskite solar cells.