Grain Boundary Healing of Organic-Inorganic Halide Perovskites for Moisture Stability

The balancing act between high electronic and low ionic transport influenced by perovskite grain boundaries

A better understanding of the materials' fundamental physical processes is necessary to push hybrid perovskite photovoltaic devices towards their theoretical limits. The role of the perovskite grain boundaries is essential to optimise the system thoroughly. The influence of the perovskite grain size and crystal orientation on physical properties and their resulting photovoltaic performance is examined. We develop a novel, straightforward synthesis approach that yields crystals of a similar size but allows the tuning of their orientation to either the (200) or (002) facet alignment parallel to the substrate by manipulating dimethyl sulfoxide (DMSO) and tetrahydrothiophene-1-oxide (THTO) ratios. This decouples crystal orientation from grain size, allowing the study of charge carrier mobility, found to be improved with larger grain sizes, highlighting the importance of minimising crystal disorder to achieve efficient devices. However, devices incorporating crystals with the (200) facet exhibit an s-shape in the current density-voltage curve when standard scan rates are used, which typically signals an energetic interfacial barrier. Using the drift-diffusion simulations, we attribute this to slower-moving ions (mobility of 0.37 × 10-10 cm2 V-1 s-1) in combination with a lower density of mobile ions. This counterintuitive result highlights that reducing ion migration does not necessarily minimise hysteresis.

Multifunctional Two-Dimensional Benzodifuran-Based Polymer for Eco-Friendly Perovskite Solar Cells Featuring High Stability

Perovskite solar cells (PSCs) have been regarded as an exceptional renewable energy conversion technology due to their rapidly increasing photovoltaic efficiency, while their practical application is highly retarded by their intrinsic instability and potential lead ion leakage. Here, a two-dimensional (2D) π-conjugated benzodifuran-based polymer, PBDFP-Bz, is adopted to modify the perovskite film. Note that PBDFP-Bz could neutralize surface defects, fine-tune interfacial energetics, and hamper moisture ingression into the perovskite film. Therefore, high-quality perovskite films featuring reduced trap state density and enhanced moisture tolerance could be obtained after modification via PBDFP-Bz. Consequently, PBDFP-Bz-modified devices deliver a higher efficiency of 21.73% versus 19.55% of control ones. Meanwhile, PBDFP-Bz-modified devices can preserve 82.7 and 90.8% of their initial efficiency under continuous heating at 85 °C or light soaking for 500 h. However, the corresponding retained values of control devices are only 56.4 and 70.2%, respectively. Moreover, PBDFP-Bz can effectively prevent the leakage of lead ions in modified devices relative to control ones. This work not only reveals that PBDFP-Bz features high potential for fabricating high-performance and robust PSCs but also indicates that 2D π-conjugated benzodifuran-based polymers can endow PSCs with great security for sustainable development without the concern of lead ion leakage.

Unnatural Hygroscopic Property of Nicotinic Acid by Restructuring Molecular Density: Self-Healing Halide Perovskites

An unnatural hygroscopic property of nonhygroscopic nicotinic acid (NA) is demonstrated by tuning the intermolecular distance. After addition of NA into methylammonium lead iodide, (MAPbI₃) NA molecules are preferentially aligned on the interface of the three-dimensional (3D) MAPbI₃ crystal structure by a hydrogen bond. This unique behavior allows NA to be used as a versatile additive to improve the water durability of MAPbI₃. After exposure under a high humidity atmosphere (RH 100%, 35 °C), MAPbI₃ films with NA exhibited self-healing phenomena against moisture while bare MAPbI₃ rapidly lost its own intrinsic property. Density functional theory (DFT) calculations were conducted to reveal how H₂O molecules can effectively be absorbed by NA according to its planar molecular density. Also, further optimization of photovoltaic device performances was carried out by investigating the relationship between NA concentration and additive alignment.

Moisture-Triggered Self-Healing Flexible Perovskite Photodetectors with Excellent Mechanical Stability

Flexible devices are urgently required to meet the demands of next-generation optoelectronic devices and metal halide perovskites are proven to be suitable materials for realizing flexible photovoltaic devices. However, the tolerance to moisture corrosion and repeated mechanical bending remains a critical challenge for flexible perovskite devices. Herein, a self-healing formamidinium lead iodide (FAPbI₃ ) film is fabricated to cure mechanical damage by absorbing moisture from the surrounding environment. A poly(vinyl alcohol) microscaffold is designed not only to stabilize the black phase of the FAPbI₃ film but also to endow it with self-healing ability in a humid environment. The photodetector based on a self-healing film exhibits a high responsivity of 11.3 A W^-1 and recovers to over 90% of the initial responsivity after the self-healing process. This work provides an effective self-healing strategy to stabilize the operation of flexible perovskite devices under normal high-humidity environmental conditions.

High-Valent Iodoplumbate-Rich Perovskite Precursor Solution via Solar Illumination for Reproducible Power Conversion Efficiency

The power conversion efficiency (PCE) of solution-processed organic-inorganic hybrid perovskite solar cells has been drastically improved. Despite this considerable progress, systematic research on precursor solution chemistry and its effects on photovoltaic parameters has been limited thus far. Herein, we report on the tracking of changes in chemical species in a precursor solution under solar illumination and investigate the correlation between the equilibrium change and the corresponding perovskite film formation. The illuminated perovskite precursors display a higher density of high-valent iodoplumbate, where the resulting perovskite film exhibits reduced defect density with uniform film formation. Conclusively, the perovskite solar cells prepared by the photoaged precursor solution demonstrate not only improved average PCE but also enhanced reproducibility with a narrow PCE distribution. This discovery shows robust control of perovskite precursor solutions from a simple treatment and suggests that the resulting uniform film may be applicable to various halide perovskite-based devices.