π‑Conjugated Lewis Base for Efficient Tin Halide Perovskite Solar Cells with Retarded Sn²⁺ Oxidation

Lead-free tin halide perovskite solar cells (TPSCs) have driven much research attention for their environmental friendliness. However, the low efficiency and large open-circuit voltage (Voc) deficit limit their further development. Here, we introduced a π-conjugated Lewis base, 1H-pyrrolo[2,3-b]pyridin-6-ylaamine (1H6An), a N donor for the unique electron-donating role of pyridine and pyrrole N with unpaired lone pair electrons to interact with the tin halide perovskites and thus retard the oxidation of Sn2+ during the aging process of precursors. Meanwhile, the interaction stabilized the perovskite lattice and decreased the microstrain of deposited films. The carrier kinetics further revealed a notably enhanced carrier extraction and transport as well as decreased nonradiative recombination with 1H6An. Consequently, this approach delivered an efficiency of 13.28% with a remarkable Voc enhancement from 853 to 907 mV. Meanwhile, the 1H6An device exhibited an extended lifespan of over 2500 h with around 90% retention of its initial value in a N2 atmosphere

Regulating the Crystallization and Carrier Dynamics for High-Performance Quasi-2D Tin Perovskite Solar Cells

Compared with three-dimensional (3D) tin halide perovskite, quasi-two-dimensional (2D) tin halide perovskite shows high stability and low defect density by introducing bulky organic spacers, which is beneficial to realize efficient and stable tin perovskite solar cells (TPSCs). However, the competitive growth between low-dimensional and three-dimensional (3D) structures leads to a complex and uncontrollable crystallization process, thus leading to the random orientation, disordered structure, and poor carrier dynamics in the corresponding devices. Here, we proposed a gradient thermal annealing (GTA) to deposit high-quality tin halide perovskite films with stable structure and low defect density by controlling the crystal growth process. Femtosecond transient absorptions confirmed that this strategy can adjust the growth speed of perovskites with different dimensions, and reduce the proportion of small n-phases which tend to grow parallel to the substrate. This further facilitated the charge transfer and enhanced the charge carrier transport and extraction. As a result, the power conversion efficiency (PCE) of the corresponding quasi-2D (⟨n⟩ = 10) Ruddlesden–Popper (RP) TPSCs was increased from 9.14% to 12.05% with strengthened environmental stability. Notably, this approach is also applicable in both RP and Dion-Jacobson (DJ) quasi-2D TPSCs, which provides a method to high efficiency quasi-2D TPSCs by regulating the carrier transport

Novel PHA Organic Spacer Increases Interlayer Interactions for High Efficiency in 2D Ruddlesden–Popper CsPbI₃ Solar Cells

The two-dimensional (2D) Ruddlesden–Popper (RP) CsPbI3 with hydrophobic organic spacers can significantly improve the environmental and phase stability of photovoltaic devices by suppressing ion migration and inducing steric hindrance. However, due to the multiple-quantum-well structure, these spacer cations lead to weak interactions in 2D RP CsPbI3, which seriously affect the carrier transport. Here, a novel N–H-group-rich phenylhydrazine spacer, namely, PHA, was developed for 2D RP CsPbI3 perovskite solar cells (PSCs). A series of characterizations confirm that the 2D perovskites using PHA spacers enhanced the N–H···I hydrogen-bonding interaction between the organic spacer cations and the [PbI6]4– inorganic layer and accelerated the crystallization rate of the perovskite film, which was beneficial to the preparation of high-quality films with preferred vertical orientation, large grain size, and dense morphology. Meanwhile, the trap state density of the as-prepared 2D RP perovskite films is significantly reduced to enable efficient charge carrier transport. As a result, the (PHA)2Cs4Pb5I16 PSCs achieved a performance of 16.23% with good environmental stability. This work provides a simple organic spacer selection scheme to realize interaction optimization in 2D RP CsPbI3 to develop efficient and stable PSCs