Intermediate Phase Free α-FAPbI3 Perovskite via Green Solvent Assisted Perovskite Single Crystal Redissolution Strategy

Ethanol purification enables high-quality α-phase FAPbI3 perovskite microcrystals for commercial photovoltaic applications

Reliable quality and sustainable processes must be developed for commodities to enter the commercial stage. For next-generation photovoltaic applications such as perovskite solar cells, it is essential to manufacture high-quality photoactive perovskites via eco-friendly processes. We demonstrate that ethanol, an ideal green solvent, can be applied to yield efficient alpha-phase FAPbI3 perovskite microcrystals.

Room Temperature Ionic Liquid Capping Layer for High Efficiency FAPbI3 Perovskite Solar Cells with Long-Term Stability

Ionic liquid salts (ILs) are generally recognized as additives in perovskite precursor solutions to enhance the efficiency and stability of solar cells. However, the success of ILs incorporation as additives is highly dependent on the precursor formulation and perovskite crystallization process, posing challenges for industrial-scale implementation. In this study, a room-temperature spin-coated IL, n-butylamine acetate (BAAc), is identified as an ideal passivation agent for formamidinium lead iodide (FAPbI3) films. Compared with other passivation methods, the room-temperature BAAc capping layer (BAAc RT) demonstrates more uniform and thorough passivation of surface defects in the FAPbI3 perovskite. Additionally, it provides better energy level alignment for hole extraction. As a result, the champion n-i-p perovskite solar cell with a BAAc capping layer exhibits a power conversion efficiency (PCE) of 24.76%, with an open-circuit voltage (Voc) of 1.19 V, and a Voc loss of ≈330 mV. The PCE of the perovskite mini-module with BAAc RT reaches 20.47%, showcasing the effectiveness and viability of this method for manufacturing large-area perovskite solar cells. Moreover, the BAAc passivation layer also improves the long-term stability of unencapsulated FAPbI3 perovskite solar cells, enabling a T80 lifetime of  3500 h when stored at 35% relative humidity at room temperature in an air atmosphere.

Room Temperature Crystallized Phase-Pure α-FAPbI3 Perovskite with In-Situ Grain-Boundary Passivation

Energy loss in perovskite grain boundaries (GBs) is a primary limitation toward high-efficiency perovskite solar cells (PSCs). Two critical strategies to address this issue are high-quality crystallization and passivation of GBs. However, the established methods are generally carried out discretely due to the complicated mechanisms of grain growth and defect formation. In this study, a combined method is proposed by introducing 3,4,5-Trifluoroaniline iodide (TFAI) into the perovskite precursor. The TFAI triggers the union of nano-sized colloids into microclusters and facilitates the complete phase transition of α-FAPbI3 at room temperature. The controlled chemical reactivity and strong steric hindrance effect enable the fixed location of TFAI and suppress defects at GBs. This combination of well-crystallized perovskite grains and effectively passivated GBs leads to an improvement in the open circuit voltage (Voc ) of PSCs from 1.08 V to 1.17 V, which is one of the highest recorded Voc without interface modification. The TFAI-incorporated device achieved a champion PCE of 24.81%. The device maintained a steady power output near its maximum power output point, showing almost no decay over 280 h testing without pre-processing.

Strain Engineering for Electrocatalytic Overall Water Splitting

Strain engineering is a novel method that can achieve superior performance for different applications. The lattice strain can affect the performance of electrochemical catalysts by changing the binding energy between the surface-active sites and intermediates and can be affected by the thickness, surface defects and composition of the materials. In this review, we summarized the basic principle, characterization method, introduction strategy and application direction of lattice strain. The reactions on hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are focused. Finally, the present challenges are summarized, and suggestions for the future development of lattice strain in electrocatalytic overall water splitting are put forward.

Dual Buried Interface Engineering for Improving Air-Processed Inverted FAPbI3 Perovskite Solar Cells

Fabricating perovskite solar cells (PSCs) in an ambient environment provides low-cost preparation routes for solar cells that are suitable for large-scale production. Compared with methylammonium (MA)- based perovskite materials, formamidinium lead iodide (FAPbI3) possesses a more favorable bandgap for light harvesting and better thermostability. However, the phase transition from the α-phase to the δ-phase easily occurs, making it challenging for ambient-air processing. Herein, we develop a buried interface engineering strategy via two molecules including 1,4-bis(diphenylphosphino)butane (DPPB) as well as [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) to optimize air-processed inverted FAPbI3 PSCs. This strategy regulates the crystallization process of the air-fabricated FAPbI3 perovskite film, leading to a purer α-phase with significantly enhanced crystallinity and enlarged grain sizes. Apart from improving the bulk perovskite film, the defects at the NiOx/perovskite interface are passivated, and the energy levels are better matched in the modified device, which facilitates efficient carrier extraction. Resultantly, the target device processed in the open air achieves a dramatically improved power conversion efficiency from 11.37% to 18.45%, in association with an enhanced device stability.

Epitaxial Growth of α-FAPbI3 at a Well-Matched Heterointerface for Efficient Perovskite Solar Cells and Solar Modules

Although the FAPbI3 perovskite system exhibits an impressive optoelectronic characteristic and thermal stability because of its energetically unstable black phase at room temperature, it is considerably challenging to attain a controllable and oriented nucleation of α-FAPbI3 . To overcome this challenge, a 2D perovskite with a released inorganic octahedral distortion designed by weakening the hydrogen interactions between the organic interlayer and [PbI6 ]4- octahedron is presented in this study. A highly matched heterointerface can be formed between the (002) facet of the 2D structure and the (100) crystal plane of the cubic α-FAPbI3 , thereby lowering the crystallization energy and inducing a heterogeneous nucleation of α-FAPbI3 . This "epitaxial growth" mechanism results form the highly preferred crystallographic orientation of the (100) facets, improved crystal quality and film uniformity, substantially increased charge transporting characteristics, and suppressed nonradiative recombination losses. An impressive power conversion efficiency (PCE) of 25.4% (certified 25.2%) is achieved using target PSCs, which demonstrates outstanding ambient and operational stability. The feasibility of this strategy is proved for the scalable deposition of homogeneous and high-quality perovskite thin films by demonstrating the remarkably increased PCE of the large-area perovskite solar module, from 18.2% to 20.1%.

Crystallization Regulation by Self-Assembling Liquid Crystal Template Enables Efficient and Stable Perovskite Solar Cells

It is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1-Dodecyl-3-methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC-modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.

Controlling Thin Film Morphology Formation during Gas Quenching of Slot-Die Coated Perovskite Solar Modules

Transferring record power conversion efficiency (PCE) >25% of spin coated perovskite solar cells (PSCs) from the laboratory scale to large-area photovoltaic modules requires significant advances in scalable fabrication techniques. In this work, we demonstrate the fundamental interrelation between drying dynamics of slot-die coated precursor solution thin films and the quality of resulting slot-die coated gas-quenched polycrystalline perovskite thin films. Well-defined drying conditions are established using a temperature-stabilized, movable table and a flow-controlled, oblique impinging slot nozzle purged with nitrogen. The accurately deposited solution thin film on the substrate is recorded by a tilted CCD camera, allowing for in situ monitoring of the perovskite thin film formation. With the tracking of crystallization dynamics during the drying process, we identify the critical process parameters needed for the design of optimal drying and gas quenching systems. In addition, defining different drying regimes, we derive practical slot jet adjustments preventing gas backflow and demonstrate large-area, homogeneous, and pinhole-free slot-die coated perovskite thin films that result in solar cells with PCEs of up to 18.6%. Our study reveals key interrelations of process parameters, e.g., the gas flow and drying velocity, and the exact crystallization position with the morphology formation of fabricated thin films, resulting in a homogeneous performance of corresponding 50 × 50 mm2 solar minimodules (17.2%) with only minimal upscaling loss. In addition, we validate a previously developed model on the drying dynamics of perovskite thin films on small-area slot-die coated areas of ≥100 cm2. The study provides methodical guidelines for the design of future slot-die coating setups and establishes a step forward to a successful transfer of solution processes towards industrial-scale deposition systems beyond brute force optimization.