Black orthorhombic (B-γ) CsSnI3 with low toxicity and excellent optoelectronic properties is a promising candidate for perovskite solar cell (PSC). However, the performance of the B-γ CsSnI3-based PSCs is much lower than their lead-based or organotin-based counterparts due to the heavy self-doping of Sn2+ to form Sn4+ under ambient-air conditions. Here, this undesirable oxidation in CsSnI3 is restricted by engineering the localized electron density with phthalimide (PTM) additive. The lone electron pairs of NH and two CO units of PTM are designed to form trigeminal coordination bonding with Sn2+, resulting in reduced defect density and relatively grain-ordered perovskite film. The champion efficiencies of 10.1% and 9.6% are obtained for the modified rigid and flexible B-γ CsSnI3-based PSCs, respectively. These encapsulated devices maintain 94.3%, 83.4%, and 81.3% of their initial efficiencies under inert (60 days), ambient (45 days), and 1 Sun continuous illumination at ∼70 °C (2000 min) conditions, respectively.

Fullerene derivative, such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM), is widely used as an electron-transport layer (ETL) in inverted perovskite solar cell (PSC). However, its low electron mobility, complexity in achieving quality film formation, and severe nonradiative recombination at perovskite/PCBM interface due to the large electron capture region, lead to lower efficiency for inverted PSCs compared to the normal structures. Herein, we demonstrate an effective and practical strategy to overcome these challenges. Conjugated n-type polymeric materials are mixed together with PCBM to form a homogeneous bulk-mixed (HBM) continuous film with high electron mobility and suitable energy level. HBM film is found to completely cap the perovskite surface to enhance the electron extraction. The critical electron capture radius of the HBM decreases to 12.52 nm from 14.89 nm of PCBM due to the large relative permittivity, resulting in reduced nonradiative recombination at perovskite/ HBM interface. The efficiency of inverted PSCs with HBM ETLs exceeds 20.6% with a high fill factor of 0.82. Further, the stability of devices is improved owing to the high hydrophobicity of the HBM ETLs. Under ambient air condition after 45 days, the efficiency of inverted PSCs based on HBM remains 80% of the initial value. This is significantly higher than the control devices which retain only 48% of the initial value under similar aging conditions. We believe these breakthroughs in improving efficiency and stability of inverted PSCs will expedite their transition.

Solution processability of photoactive halide perovskites differentiates them from traditional inorganic semiconducting materials that require multiple post-processing steps such as thermal/vacuum/blow- & solvent-assistant treatment. Here we report a technical breakthrough...