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The favorable contact and matching energy level at the electrode/perovskite interface as well as the high-quality perovskite film are prerequisites for high photovoltaic performance perovskite solar cells (PSCs). Herein, an innovative interface engineering strategy has been proposed to modify TiO2 as well as the perovskite film simultaneously by introducing ammonium chloride (AC), which not only improves the contact and energy level matching at the TiO2/perovskite interface but also provides a high-quality perovskite film with larger grain size by regulating the crystallization kinetics of CsPbBr3. Furthermore, chlorine anions in AC tend to combine with TiO2 to passivate its surface defects; the ammonium cation can bond with the uncoordinated ionic defects of perovskite. As a result, a remarkably enhanced charge extraction and retarded charge recombination within inorganic CsPbBr3 PSCs is acquired through the interface engineering of AC, and the power conversion efficiency of the modified device is increased from the original 6.59% to 9.60%. By compensating the energy level at the perovskite/carbon interface by setting an efficient hole-transporting layer of zinc phthalocyanine (ZnPc), the best efficiency up to 10.12% was achieved for the device with AC and ZnPc interface modification, which is much higher than 7.87% efficiency for the ZnPc-only PSCs, further demonstrating the important positive effects of AC modification on device performance. Moreover, the optimized device without any encapsulation presents an exceptional long-term stability under persistent attack by 80% RH air atmosphere at 25 °C for 720 h. [ABSTRACT FROM AUTHOR]

Carbon‐based CsPbBr3 perovskite solar cells (PSCs) without hole‐transporting layers (HTLs) have aroused extensive attention due to their low manufacturing cost and prominent ambient stability. However, the defects of perovskite film and the poor charge extraction within PSCs result in severe charge recombination, which restricts the further enhancement of device efficiency. In view of this critical point, a compositional engineering of CsPbBr3 perovskite via doping with Cl− ions is presented herein to decrease the trap states and enhance the charge extraction. It is revealed that the doping of Cl− ions not only enlarges the grain size and thereby reduces the trap‐state density, but also optimizes the energy‐level alignment and improves the hole mobility of the perovskite film, leading to an evidently suppressed charge recombination and improved charge extraction and transportation. As a result, a champion power conversion efficiency (PCE) of 9.73% is achieved for carbon‐based HTL‐free CsPbBr2.98Cl0.02 PSC, yielding a marked enhancement in comparison with 6.69% efficiency for the control. Meanwhile, the thermal and moisture stabilities of unencapsulated CsPbBr2.98Cl0.02 PSC are improved, maintaining 93% and 95% of the initial PCE after expose to air atmosphere with 80% relative humidity (RH) and at 80 °C over 60 days, respectively. [ABSTRACT FROM AUTHOR]

The defect passivation of perovskite films is an efficacious way to further boost the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). In this work, ionic liquids (ILs) of 1-butyl-2,3-dimethylimidazolium chloride ([BMMIm]Cl) are used as a modification layer in perovskite films in carbon-based CsPbBr 3 PSCs without a hole-transporting material (HTM) for passivating the surface defects. The preliminary results demonstrate that the [BMMIm]Cl modifier passivates the surface defects of the perovskite film and reduces the valence band of perovskite close to the work function of the carbon electrode, which causes a remarkably inhibited nonradiative and radiative charge recombination, improved energy-level matching, and decreased energy loss. After optimization, a champion efficiency of 9.92% with a V oc as high as 1.61 V is achieved for the [BMMIm]Cl tailored carbon-based CsPbBr 3 PSC without HTM, which is improved by 61.3% in comparison with 6.15% for the control device. Furthermore, the encapsulation-free PSC presents good long-term stability after storage in an air atmosphere with 70% RH at 20 °C or 0% RH at 80 °C as well as under continuous illumination conditions for 30 days. The significantly improved PCE and stability in high humidity or temperature suggest that the perovskite passivation by ILs is an effective strategy for fabricating high-PCE and stable PSCs.