Cation reactivity inhibits perovskite degradation in efficient and stable solar modules

Fluid Chemistry of Metal Halide Perovskites

Solution-processed metal halide perovskites (MHPs) have been rapidly developed worldwide, with much attention to fluid dynamic, fluid crystallization, and fluid interfaces, all falling within the realm of fluid chemistry. It is widely recognized that the theory of fluid chemistry has been proven to provide an effective means for the improvement of perovskite crystallization and the enhancement of perovskite solar cells (PSCs) performance. In this review, the fluid behavior, microfluidic synthesis, and aging process of perovskite materials are first investigated, with emphasis on the related improvement methods and chemical mechanisms. Second, the internal crystallization chemistry, external interface chemistry, and the large-area PSCs based on the fluid chemistry are discussed. Finally, four specific directions for future studies of fluid chemistry of MHPs are proposed, aiming to harness the theoretical advantages of fluid chemistry and contribute to the industrialization of PSCs.

Mitigating Carrier and Energy Losses via Interface Modulator Toward High-Performance Perovskite Solar Cells

Interface engineering has become the main force in reforming the photogenerated carrier and energy losses in perovskite solar cells (PSCs). Here, a multifaceted hole-selective molecule C-DPT, is designed and synthesized with methoxy-triphenylamine-carbazole and diphenyl-triazine units, which is employed as the interface modulator between perovskite and hole transport layer. The introduction of C-DPT endows the perovskite/hole transport layer heterojunction with a more flat physical contact, lower trap density, and faster hole extraction. The combined theoretical and experimental results decipher that C-DPT possessing the compatible contact and favorable perovskite binding ability can efficiently boost the interfacial defect restoration, compensate the interfacial energetic offset, and promote the interfacial carrier transportation. As a result, C-DPT-modified PSC delivers a champion power conversion efficiency of 24.02% in conjunction with the pronouncedly improved long-term ambient, thermal, and humidity stability.

Crystallization Modulation and Comprehensive Defect Passivation by Carbonyl Functionalized Spacer Cation Towards High-Performance Inverted Perovskite Solar Cells

The inverted cesium/formamidinium (CsFA)-based methylammonium-free perovskite solar cells possess great potential in simultaneously realizing high power conversion efficiency (PCE) and excellent stability. However, the uncontrollable crystallization process and poor film quality hinder further enhancement of photovoltaic performance and operational stability. Herein, we propose a synergistic modulation strategy of perovskite crystallization and the defects at grain boundaries (GBs) and interface by using a novel carbonyl functionalized spacer cation. L-Alanine benzyl ester hydrochloride (L-ABEHCl) containing carbonyl functionalized ammonium cation is incorporated into perovskite precursor solution, increasing the nucleation rate and reducing the crystal growth rate because of its strong interaction with precursor components, leading to increased grain size and crystallinity. No 2D perovskite is formed for L-ABEHCl as additive whereas 2D perovskite is formed upon L-ABEHCl post-treatment. It is revealed that FA+ and Cs+ in precursor solution suppress the formation of 2D perovskite. As a result, the L-ABEHCl passivates the defects at GBs in the form of organic salts and passivates interface defects in the form of 2D perovskite. Due to minimized carrier nonradiative recombination losses, the inverted devices using synergistic modulation strategy achieve a maximum PCE of 25.77 % (certified stabilized PCE of 25.59 %), which is one of the highest PCEs ever reported for the devices based on vacuum flash evaporation method. The unencapsulated target device maintains 90.85 % of its initial PCE after 2300 h of continuous maximum power point tracking, among the most excellent stabilities accomplished by inverted devices.

Self-cleaning Spiro-OMeTAD via multimetal doping for perovskite photovoltaics

Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) are usually achieved using organic spiro-OMeTAD. However, conventional doping with hygroscopic dopants (LiTFSI and tBP) leads to compromised device stability. We introduce a synergistic mixed doping strategy that utilizes a combination of metal-TFSI dopants-LiTFSI, KTFSI, NaTFSI, Ca(TFSI)2, and Mg(TFSI)2-to enhance doping efficiency while effectively removing hygroscopic contaminants from the Spiro-OMeTAD solution. This approach achieves PCEs exceeding 25% and significantly improves stability under harsh environmental conditions. Notably, Ca(TFSI)2 and Mg(TFSI)2 facilitate enhanced oxidative doping, while NaTFSI promotes interstitial doping in the bulk perovskite. Additionally, KTFSI serves as a catalytic agent, lowering the reaction energy barrier for the other dopants, thereby accelerating spiro-OMeTAD ion radical production. These findings underscore the potential of synergistic doping in optimizing the performance and longevity of photovoltaic devices.

Light in heart, forge ahead-Professor Rui Wang's adventures in perovskite solar cell frontiers

EDITORIAL

As depicted in ancient Greek mythology, Prometheus couldn't bear the sight of humanity struggling in the darkness, crafted a long reed, and took the risk of approaching the sun to steal fire. He fearlessly brought this light to the world, defying what Zeus had ordered the gods not to do. His brave act ushered in the dawn of civilization for mankind. In this issue of "Light People", Professor Rui Wang is invited to share stories about his adventures in improving perovskite solar cells for the full utilization of sunlight in daily lives, much like Prometheus bringing the gift of light to humanity. Perovskite solar cells hold great potential for both civilian applications and commercial purposes, such as rooftop solar panels, solar chargers, and solar-powered vehicles.

C60-based ionic salt electron shuttle for high-performance inverted perovskite solar modules

Although C60 is usually the electron transport layer (ETL) in inverted perovskite solar cells, its molecular nature of C60 leads to weak interfaces that lead to non-ideal interfacial electronic and mechanical degradation. Here, we synthesized an ionic salt from C60, 4-(1',5'-dihydro-1'-methyl-2'H-[5,6] fullereno-C60-Ih-[1,9-c]pyrrol-2'-yl) phenylmethanaminium chloride (CPMAC), and used it as the electron shuttle in inverted PSCs. The CH2-NH3+ head group in the CPMA cation improved the ETL interface and the ionic nature enhanced the packing, leading to ~3-fold increase in the interfacial toughness compared to C60. Using CPMAC, we obtained ~26% power conversion efficiencies (PCEs) with ~2% degradation after 2,100 hours of 1-sun operation at 65°C. For minimodules (four subcells, 6 centimeters square), we achieved the PCE of ~23% with <9% degradation after 2,200 hours of operation at 55°C.

Extendable Synthesis of Organic Cations for In Situ Construction of Hybrid Metal Halides with Near-Unity Photoluminescence and Strong Second Harmonic Generation

The A-site organic components of organic-inorganic hybrid metal halides (OIHMHs) significantly impact their crystal structure and optoelectronic properties. However, chemical modification of A-site cations has been mostly limited to commercial organic precursors, which restricts the structural variability of OIHMHs for optimal functionalities. Herein we have proposed an extendable synthesis approach to the direct procurability of various organic cations with desireable structures for the in situ construction of a library of OIHMH materials. The template condensation reaction between dimethyl sulfoxide and acetone derivatives yields A-site organic cations with exquisite control of modularization and regioselectivity within the OIHMH crystallization system. The as-fabricated OIHMHs demonstrated highly efficient linear optical photoluminescence or nonlinear optical second harmonic generation, promising potential applications in photonic devices. This in situ synthetic strategy offers a structural extension of OIHMHs and establishes a fundamental methodological platform for screening functional OIHMH materials.

1.5D Chiral Perovskites Mediated by Hydrogen-Bonding Network with Remarkable Spin-Polarized Property

In this study, we developed new chiral hybrid perovskites, (R/S-MBA)(GA)PbI4, by incorporating achiral guanidinium (GA+) and chiral R/S-methylbenzylammonium (R/S-MBA+) into the perovskite framework. The resulting materials possess a distinctive structural configuration, positioned between 1D and 2D perovskites, which we describe as 1.5D. This structure is featured by a hydrogen-bonding-network-induced arrangement of zigzag inorganic chains, further forming an organized layered architecture. The structural dimensionality affects both electronic and spin-related properties. Density functional theory (DFT) calculations reveal Rashba splitting induced by the inversion asymmetry of the crystal structure, while circularly polarized transient absorption spectroscopy confirms spin lifetime on the nanosecond timescale. Magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements demonstrate exceptional chiral-induced spin selectivity (CISS) with maximum spin polarization degrees of (92±1)% and (-94±2)% for (R-MBA)(GA)PbI4 and (S-MBA)(GA)PbI4, respectively. These findings underscore the potential of (R/S-MBA)(GA)PbI4 as promising candidates for next-generation spintronic devices, also highlight the critical role of chemical environment in sculpturing the structural dimension and spin-polarized property of chiral perovskites.

Strategic Integration of Machine Learning in the Design of Excellent Hybrid Perovskite Solar Cells

The photoelectric conversion efficiency (PCE) of perovskites remains beneath the Shockley-Queisser limit, despite its significant potential for solar cell applications. The present focus is on investigating potential multicomponent perovskite candidates, particularly on the application of machine learning to expedite band gap screening. To efficiently identify high-performance perovskites, we utilized a data set of 1346 hybrid organic-inorganic perovskites and employed 11 machine learning models, including decision trees, convolutional neural networks (CNNs), and graph neural networks (GNNs). Four descriptors were utilized for high-throughput screening: sine matrix, Ewald sum matrix, atom-centered symmetry functions (ACSF), and many-body tensor representation (MBTR). The results indicated that LightGBM and CatBoost somewhat surpassed XGBoost in decision tree models, but random forests lagged. Among the CNN models utilizing the same four descriptors, CustomCNN and VGG16 surpassed Xception, while EfficientNetV2B0 exhibited the least favorable performance. When the sine matrix and Ewald sum matrix served as adjacency matrices in GNN models, GCSConv exhibited a considerable improvement over GATConv and a slight advantage over GCNConv. Significantly, GCSConv outperformed other models when utilized with the Ewald sum matrix. The ideal combination of descriptors and algorithms identified was MBTR + CustomCNN, with an R2 of 0.94. Subsequently, three perovskites exhibiting appropriate Heyd-Scuseria-Ernzerhof (HSE06) band gaps were identified to define the defects. Among them, CH3C(NH2)2SnI3 exhibited superior performance in both vacancy and substitutional defects compared to C3H8NSnI3 and (CH3)2NH2SnI3. This high-throughput screening method with machine learning establishes a robust foundation for selecting solar materials with exceptional photoelectric properties.