Enhancing the Efficiency and Stability of Inverted Formamidinium-Cesium Lead-Triiodide Perovskite Solar Cells through Lewis Base Pretreatment of Buried Interfaces.

Mixed components of formamidinium(FA) and cesium (Cs)-based perovskite solar cells are the most hopeful for commercialization owing to their excellent operational and phase stabilities, especially for devices with inverted structure. The nonradiative recombination of carriers can be effectively suppressed through interface optimization, therefore, the performance of devices can be improved. Notably, the buried interface emerges as critical aspects such as charge transport, charge recombination kinetics, and morphology of perovskite films. This study focuses on a straightforward yet effective approach to overcome buried interface challenges between organic polymers (poly(-triarylamine) (PTAA) and FACs-based perovskite films. The PTAA substrate is pretreated with a Lewis base known as 2-butynoic acid (BA) with a C═O functional group. First, it can be an interfacial buffering layer, harmonizing stress mismatch between the perovskite and PTAA layers, consequently optimizing crystallization and improving perovskite film quality. Second, Pb2+ defect can be passivated at the buried interface of the perovskite film through binding with the C═O group of the BA molecule. This dual-function strategy leads to a substantial enhancement in both photoelectric conversion efficiency (PCE) and stability of devices. Finally, the PCE of the device-modified buried interface with BA reaches an impressive 23.33%. Furthermore, unencapsulated devices with BA treatment maintain approximately 94% of their initial efficiency after aging at maximum power point tracking for 1000 h.

Investigation of Perovskite Solar Cells Using Guanidinium Doped MAPbI3 Active Layer.

In this work, guanidinium (GA+) was doped into methylammonium lead triiodide (MAPbI3) perovskite film to fabricate perovskite solar cells (PSCs). To determine the optimal formulation of the resulting guanidinium-doped MAPbI3 ((GA)x(MA)1-xPbI3) for the perovskite active layer in PSCs, the perovskite films with various GA+ doping concentrations, annealing temperatures, and thicknesses were systematically modulated and studied. The experimental results demonstrated a 400-nm-thick (GA)x(MA)1-xPbI3 film, with 5% GA+ doping and annealed at 90 °C for 20 min, provided optimal surface morphology and crystallinity. The PSCs configured with the optimal (GA)x(MA)1-xPbI3 perovskite active layer exhibited an open-circuit voltage of 0.891 V, a short-circuit current density of 24.21 mA/cm2, a fill factor of 73.1%, and a power conversion efficiency of 15.78%, respectively. Furthermore, the stability of PSCs featuring this optimized (GA)x(MA)1-xPbI3 perovskite active layer was significantly enhanced.

Body weight-based iodinated contrast immersion timing for human fetal postmortem microfocus computed tomography.

Objectives: The aim of this study was to evaluate the length of time required to achieve full iodination using potassium tri-iodide as a contrast agent, prior to human fetal postmortem microfocus computed tomography (micro-CT) imaging. Methods: Prospective assessment of optimal contrast iodination was conducted across 157 human fetuses (postmortem weight range 2-298 g; gestational age range 12-37 weeks), following micro-CT imaging. Simple linear regression was conducted to analyse which fetal demographic factors could produce the most accurate estimate for optimal iodination time. Results: Postmortem body weight (r2 = 0.6435) was better correlated with iodination time than gestational age (r2 = 0.1384), producing a line of best fit, y = [0.0304 × body weight (g)] - 2.2103. This can be simplified for clinical use whereby immersion time (days) = [0.03 × body weight (g)] - 2.2. Using this formula, for example, a 100-g fetus would take 5.2 days to reach optimal contrast enhancement. Conclusions: The simplified equation can now be used to provide estimation times for fetal contrast preparation time prior to micro-CT imaging and can be used to manage service throughput and parental expectation for return of their fetus. Advances in knowledge: A simple equation from empirical data can now be used to estimate preparation time for human fetal postmortem micro-CT imaging.

Practical four-electron zinc-iodine aqueous batteries enabled by orbital hybridization induced adsorption-catalysis.

The successive I-/I0/I+ redox couples in the four-electron zinc-iodine aqueous battery (4eZIB) is plagued by the instability of the electrophilic I+ species, which could either be hydrolyzed or be neutralized by the I3- redox intermediates. We present an adsorption-catalysis approach that effectively suppresses the hydrolysis of ICl species and also provides an enhanced reaction kinetics to surpass the formation of triiodide ions. We elucidate that the improved stability is attributed to the pronounced orbital hybridization between the d orbitals of Fe-N4 moieties (atomic Fe supported on nitrogen doped carbon) and the p orbitals of iodine species (I2 and ICl). Such d-p orbital hybridization leads to enhanced adsorption for iodine species, increased energy barrier for proton detachment from the ICl·HOH intermediate during hydrolysis, and efficient catalysis of the iodine redox reactions with high conversion efficiency. The proposed 4eZIB demonstrates practical areal capacity (>3 mAh cm-2) with a near-unity coulombic efficiency, high energy density of 420 Wh kg-1 (based on cathode mass), and long-term stability (over 10,000 cycles). Even at -20 °C, the battery exhibits stable performance for over 1000 cycles with high iodine utilization ratio.

Spontaneous Appearance of Triiodide Covering the Topmost Layer of the Iodide Solution Interface Without Photo-Oxidation.

Ions containing iodine atoms at the vapor-aqueous solution interfaces critically affect aerosol growth and atmospheric chemistry due to their complex chemical nature and multivalency. While the surface propensity of iodide ions has been intensely discussed in the context of the Hofmeister series, the stability of various ions containing iodine atoms at the vapor-water interface has been debated. Here, we combine surface-specific sum-frequency generation (SFG) vibrational spectroscopy with ab initio molecular dynamics simulations to examine the extent to which iodide ions cover the aqueous surface. The SFG probe of the free O-D stretch mode of heavy water indicates that the free O-D group density decreases drastically at the interface when the bulk NaI concentration exceeds ∼2 M. The decrease in the free O-D group density is attributed to the spontaneous appearance of triiodide that covers the topmost interface rather than to the surface adsorption of iodide. This finding demonstrates that iodide is not surface-active, yet the highly surface-active triiodide is generated spontaneously at the water-air interface, even under dark and oxygen-free conditions. Our study provides an important first step toward clarifying iodine chemistry and pathways for aerosol formation.

Nonvolatile Memristive Effect in Few-Layer CrI3 Driven by Electrostatic Gating.

The potential of memristive devices for applications in nonvolatile memory and neuromorphic computing has sparked considerable interest, particularly in exploring memristive effects in two-dimensional (2D) magnetic materials. However, the progress in developing nonvolatile, magnetic field-free memristive devices using 2D magnets has been limited. In this work, we report an electrostatic-gating-induced nonvolatile memristive effect in CrI3-based tunnel junctions. The few-layer CrI3-based tunnel junction manifests notable hysteresis in its tunneling resistance as a function of gate voltage. We further engineered a nonvolatile memristor using the CrI3 tunneling junction with low writing power and at zero magnetic field. We show that the hysteretic transport observed is not a result of trivial effects or inherent magnetic properties of CrI3. We propose a potential association between the memristive effect and the newly predicted ferroelectricity in CrI3 via gating-induced Jahn-Teller distortion. Our work illuminates the potential of 2D magnets in developing next-generation advanced computing technologies.

Decoupling the anodic and cathodic behavior in asymmetric electrochemical hydroiodic acid decomposition cell for hydrogen production in the iodine-sulfur thermochemical cycle.

The HI section of the iodine-sulfur (I-S) thermochemical cycle for hydrogen production is one of the most energy-intensive sections and with significant material handling challenges, primarily due to the azeotrope formation and the corrosive nature of the hydroiodic acid-iodine-water mixture (HIx). As an alternative, the single-step direct electrochemical decomposition of the hydroiodic acid (HI) to generate hydrogen can circumvent the challenges associated with the conventional multistep HI section in the I-S cycle. In this work, we present new insights into the electrochemical HI decomposition process by deconvoluting the contributions from the anodic and the cathodic sections in the electrochemical cell system, specifically, the redox reactions involved and the overpotential contribution of the individual sections (anolyte and catholyte) in the overall performance. The studies on the redox reactions indicate that the HIx solution output from the Bunsen reaction section should be used as the anolyte. In contrast, aqueous HI without any iodine (I2) should be used as the catholyte. In the anodic section, the oxidation proceeds with I2 as the final oxidized species at low bias potentials. Higher positive potentials result in iodate formation along with oxygen evolution. For the catholyte section, I2 and tri-iodide ion reduction precede the hydrogen evolution reaction when I2 is present along with HI. Furthermore, the potential required for hydrogen production becomes more negative with an increasing I2/HI ratio in the catholyte. Polarization studies were conducted with simultaneous deconvolution of the anodic and cathodic behavior in a two-compartment cell. Model fitting of the polarization data revealed that the anolyte section's activation overpotential is negligibly low. In contrast, the activation overpotential requirement of the catholyte section is higher and dictates the onset of hydrogen production in the cell. Furthermore, the catholyte section dominates the total overpotential losses in the cell system. Operation in the ohmic resistance-dominated zone resulted in close to 90% current efficiency for the electrochemical HI decomposition. The results highlight that the potential for process improvement lies in reducing the ohmic resistance of the anolyte section and in lowering the activation overpotential of hydrogen evolution in the catholyte section.

Decoupling Electrochromism and Energy Storage for Flexible Quasi-Solid-State Aqueous Electrochromic Batteries with High Energy Density.

Currently, reported aqueous electrochromic batteries (ECBs) show only limited capacity with insufficient energy density and power density. Such a limitation is naturally imposed by the rationale that the cathode of ECBs stores charge by an ion intercalation/deintercalation mechanism, where the inherent inhibition of ion diffusion and structural collapse of cathode materials through repetitive charge/discharge cycles lead to low areal capacity and unsatisfactory electrochemical performance with short lifetime. Herein, we decouple the dual functions of electrochromism and energy storage in conventional cathodes of ECBs by introducing a polyaniline/triiodide composite cathode that is in situ formed by direct electrolysis of an iodide-based quasi-solid-state aqueous electrolyte during charging. When paired with a zinc metal anode, the composite cathode can synergistically utilize the electrochromic property of polyaniline, the high-efficiency energy storage of the Zn-I2 system, as well as the effective anchorage of polyiodide by polyaniline to suppress the shuttle effect of triiodide. By selecting 1-butyl-3-methylimidazolium ion (BMI+) as the cation, a liquid-solid cathode/quasi-solid-state electrolyte interface can be achieved to facilitate the interfacial charge transfer, rendering quasi-solid-state aqueous electrochromic batteries with a high areal capacity of 1363 µAh cm-2, energy density of 1650 µWh cm-2, and power density of 5186 µW cm-2.

Valence and Core Photoelectron Spectra of Aqueous I3- from Multi-Reference Quantum Chemistry.

The I3- molecule is known to undergo substantial structural reorganization upon solvation by a protic solvent, e.g., water. However, the details of this process are still controversially discussed in the literature. In the present study, we combined experimental and theoretical efforts to disentangle this controversy. The valence (5p), N4,5 (4d), and M4,5 (3d) edge photoelectron spectra were measured in an aqueous solution and computed using high-level multi-reference methods. Our previous publication mainly focused on obtaining reliable experimental evidence, whereas in the present article, we focused primarily on theoretical aspects. The complex electronic structure of I3- requires the inclusion of both static and dynamic correlation, e.g., via the multi-configurational perturbation theory treatment. However, the resulting photoelectron spectra appear to be very sensitive to problems with variational stability and intruder states. We attempted to obtain artifact-free spectra, allowing for a more reliable interpretation of experiments. Finally, we concluded that the 3d Photoelectron Spectrum (PES) is particularly informative, evidencing an almost linear structure with a smaller degree of bond asymmetry than previously reported.

Triiodide Attacks the Organic Cation in Hybrid Lead Halide Perovskites: Mechanism and Suppression.

Molecular I2 can be produced from iodide-based lead perovskites under thermal stress; triiodide, I3 - , is formed from this I2 and I- . Triiodide attacks protic cation MA+ - or FA+ -based lead halide perovskites (MA+ , methylammonium; FA+ , formamidinium) as explicated through solution-based nuclear magnetic resonance (NMR) studies: triiodide has strong hydrogen-bonding affinity for MA+ or FA+ , which leads to their deprotonation and perovskite decomposition. Triiodide is a catalyst for this decomposition that can be obviated through perovskite surface treatment with thiol reducing agents. In contrast to methods using thiol incorporation into perovskite precursor solutions, no penetration of the thiol into the bulk perovskite is observed, yet its surface application stabilizes the perovskite against triiodide-mediated thermal stress. Thiol applied to the interface between FAPbI3 and Spiro-OMeTAD ("Spiro") prevents oxidized iodine species penetration into Spiro and thus preserves its hole-transport efficacy. Surface-applied thiol affects the perovskite work function; it ameliorates hole injection into the Spiro overlayer, thus improving device performance. It helps to increase interfacial adhesion ("wetting"): fewer voids are observed at the Spiro/perovskite interface if thiols are applied. Perovskite solar cells (PSCs) incorporating interfacial thiol treatment maintain over 80% of their initial power conversion efficiency (PCE) after 300 h of 85 °C thermal stress.

Comparative Evaluation of Chemical and Photolytic Denitrosation Methods for Chemiluminescence Detection of Total N-Nitrosamines in Wastewater Samples.

N-Nitrosamines form as byproducts during oxidative water treatment and occur as impurities in consumer and industrial products. To date, two methods based on chemiluminescence (CL) detection of nitric oxide liberated from N-nitrosamines via denitrosation with acidic triiodide (HI3) treatment or ultraviolet (UV) photolysis have been developed to enable the quantification of total N-nitrosamines (TONO) in environmental water samples. In this work, we configured an integrated experimental setup to compare the performance of HI3-CL and UV-CL methods with a focus on their applicability for TONO measurements in wastewater samples. With the use of a large-volume purge vessel for chemical denitrosation, the HI3-CL method achieved signal stability and detection limits comparable to those achieved by the UV-CL method which utilized a microphotochemical reactor for photolytic denitrosation. Sixty-six structurally diverse N-nitroso compounds (NOCs) yielded a range of conversion efficiencies relative to N-nitrosodimethylamine (NDMA) regardless of the conditions applied for denitrosation. On average, TONO measured in preconcentrated raw and chloraminated wastewater samples by the HI3-CL method were 2.1 ± 1.1 times those measured by the UV-CL method, pointing to potential matrix interferences as further confirmed by spike recovery tests. Overall, our comparative assessment of the HI3-CL and UV-CL methods serves as a basis for addressing methodological gaps in TONO analysis.

Protic Amine Carboxylic Acid Ionic Liquids Additives Regulate α-FAPbI3 Phase Transition for High Efficiency Perovskite Solar Cells.

The α-phase formamidinium lead tri-iodide (α-FAPbI3 ) has become the most promising photovoltaic absorber for perovskite solar cells (PSCs) due to its outstanding semiconductor properties and astonishing high efficiency. However, the incomplete crystallization and phase transition of α-FAPbI3 substantially undermine the performance and stability of PSCs. In this work, a series of the protic amine carboxylic acid ion liquids are introduced as the precursor additives to efficiently regulate the crystal growth and phase transition processes of α-FAPbI3 . The MA2 Pb3 I8 ·2DMSO phase is inhibited in annealing process, which remarkably optimizes the phase transition process of α-FAPbI3 . It is noted that the functional groups of carboxyl and ammonium passivate the undercoordinated lead ions, halide vacancies, and organic vacancies, eliminating the deleterious nonradiative recombination. Consequently, the small-area devices incorporated with 2% methylammonium butyrate (MAB) and 1.5% n-butylammonium formate (BAFa) in perovskite show champion efficiencies of 25.10% and 24.52%, respectively. Furthermore, the large-area modules (5 cm × 5 cm) achieve PCEs of 21.26% and 19.27% for MAB and BAFa additives, indicating the great potential for commercializing large-area PSCs.

2-Amino-1,3-benzothiazole: Endo N-Alkylation with α-Iodo Methyl Ketones Followed by Cyclization.

Reactions of 2-amino-1,3-benzothiazole with aliphatic, aromatic and heteroaromatic α-iodoketones in the absence of bases or catalysts have been studied. The reaction proceeds by N-alkylation of the endocyclic nitrogen atom followed by intramolecular dehydrative cyclization. The regioselectivity is explained and the mechanism of the reaction is proposed. A number of new linear and cyclic iodide and triiodide benzothiazolium salts have been obtained and their structure proved by NMR and UV spectroscopy.

Kinetic-Controlled Crystallization of α-FAPbI3 Inducing Preferred Crystallographic Orientation Enhances Photovoltaic Performance.

Crystallization kinetic controls the crystallographic orientation, inducing anisotropic properties of the materials. As a result, preferential orientation with advanced optoelectronic properties can enhance the photovoltaic devices' performance. Although incorporation of additives is one of the most studied methods to stabilize the photoactive α-phase of formamidinium lead tri-iodide (α-FAPbI3 ), no studies focus on how the additives affect the crystallization kinetics. Along with the role of methylammonium chloride (MACl) as a "stabilizer" in the formation of α-FAPbI3 , herein, the additional role as a "controller" in the crystallization kinetics is pointed out. With microscopic observations, for example, electron backscatter diffraction and selected area electron diffraction, it is examined that higher concentration of MACl induces slower crystallization kinetics, resulting in larger grain size and [100] preferred orientation. Optoelectronic properties of [100] preferentially oriented grains with less non-radiative recombination, a longer lifetime of charge carriers, and lower photocurrent deviations in between each grain induce higher short-circuit current density (Jsc ) and fill factor. Resulting MACl40 mol% attains the highest power conversion efficiency (PCE) of 24.1%. The results provide observations of a direct correlation between the crystallographic orientation and device performance as it highlights the importance of crystallization kinetics resulting in desirable microstructures for device engineering.

Nanoscale Thermal Strain Engineering-Driven Ferroelastic Domain Evolution in CH3NH3PbI3 Perovskites.

A local thermal strain engineering approach via an ac-heated thermal probe was incorporated into methylammonium lead triiodide (MAPbI3) crystals and acts as a driving force for ferroic twin domain dynamics, local ion migration, and property tailoring. Periodically, striped ferroic twin domains and their dynamic evolutions were successfully induced by local thermal strain and high-resolution thermal imaging, giving decisive evidence of the ferroelastic nature in MAPbI3 perovskites at room temperature. Local thermal ionic imaging and chemical mappings demonstrate that domain contrasts are from local methylammonium (MA+) redistribution into the stripes of chemical segregation in response to the local thermal strain fields. The present results reveal an inherent coupling among local thermal strains, ferroelastic twin domains, local chemical-ion segregations, and physical properties and offer a potential path to improve the functionality of metal halide perovskite-based solar cells.

Magnetic Amplification at Yb3+ "Designer Defects" in the van der Waals Ferromagnet CrI3.

The two-dimensional (2D) van der Waals ferromagnet CrI3 has been doped with the magnetic optical impurity Yb3+ to yield materials that display sharp multiline Yb3+ photoluminescence (PL) controlled by the magnetism of CrI3. Magneto-PL shows that Yb3+ magnetization is pinned to the magnetization of CrI3. An effective internal field of ∼10 T at Yb3+ is estimated, attributed to strong in-plane Yb3+-Cr3+ superexchange coupling. The anomalously low energy of Yb3+ PL in CrI3 reflects relatively high Yb3+-I- covalency, contributing to Yb3+-Cr3+ superexchange coupling. The Yb3+ PL energy and line width both reveal the effects of spontaneous zero-field CrI3 magnetic ordering within 2D layers below TC, despite the absence of net magnetization in multilayer samples. These results illustrate the use of optical impurities as "designer defects" to introduce unique functionality to 2D magnets.

Dehalogenation reactions between halide salts and phosphate compounds.

Reactions between phosphoric acid [H3PO4] or ammonium hydrogen phosphates [i.e., NH4H2PO4, (NH4)2HPO4] and halide salts can be used to dehalogenate (remove halides from) salt-based waste streams, where the process of removing halides yields products that have more efficient disposal pathways for repository storage. In this context, the term efficiency is defined as higher waste loadings and simplified immobilization processes with potential for recycle of certain salt components (e.g., 37Cl as H37Cl or NH4 37Cl). The main streams identified for these processes are nuclear wastes generated during electrochemical reprocessing of used nuclear fuel as well as used halide salts from molten salt reactor operation. The potential byproducts of these reactions are fairly consistent across the range of halide species (i.e., F, Cl, Br, I) where the most common are hydrogen halides [e.g., HCl(g)] or ammonium halides (e.g., NH4Cl). However, trihalide compounds (e.g., NCl3), nitrogen triiodide ammine adducts [NI3·(NH3) x ], and ammonium triiodide (NH4I3) are also possible. Several of these byproducts (i.e., NCl3, NBr3, NI3, and NH4I3) are shock-sensitive contact explosives so their production in these processes must be tracked and carefully controlled, which includes methods of immediate neutralization upon production such as direct transport to a caustic scrubber for dissolution. Several benefits arise from utilizing H3PO4 as the phosphate additive during dehalogenation reactions for making iron phosphate waste forms including more oxidized iron (higher Fe3+:Fe2+ ratios), higher chemical durabilities, and the avoidance of trihalides, but the byproducts are hydrogen halides, which are corrosive and require special handling.

Low-Temperature Phase-Transition for Compositional-Pure α-FAPbI3 Solar Cells with Low Residual-Stress and High Crystal-Orientation.

Transition of δ-phase formamidinium lead triiodide (δ-FAPbI3 ) to pure α-phase FAPbI3 (α-FAPbI3 ) typically requires high processing temperature (150 °C), which often results in unavoidable residual stress. Besides, using methylammonium chloride (MACl) as additive in fabrication will cause MA residue in the film, compromising the compositional purity. Here, a stress-released and compositional-pure α-FAPbI3 thin-film is fabricated using 3-chloropropylammonium chloride (Cl-PACl) by two-step annealing. The 2D template of n = 2 can preferentially form in perovskite with the introduction of Cl-PACl at a temperature as low as 80 °C. Such a 2D template can guide the free components to form ordered α-FAPbI3 and promote the transition of the formed δ-FAPbI3 to α-FAPbI3 by reducing the phase transition energy. As a result, the obtained perovskite films via low-temperature phase-transition have a high degree of crystal orientation and reduced residual stress. More importantly, most of the Cl-PACl is volatilized during the subsequent high-temperature annealing process accompanied by the disintegration of the 2D templates. The residual trace of Cl-PA+ is mainly concentrated at the grain boundary near the perovskite surface layer, stabilizing α-FAPbI3 and passivating defects. Perovskite solar cell based on pure α-FAPbI3 achieves a power conversion efficiency of 23.03% with excellent phase stability and photo-stability.

Development of a Polymeric Film Entrapping Rose Bengal and Iodide Anion for the Light-Induced Generation and Release of Bactericidal Hydrogen Peroxide.

A series of poly(2-hydroxyethyl methacrylate) (PHEMA) thin films entrapping photosensitizer Rose Bengal (RB) and tetrabutylammonium iodide (TBAI) have been synthetized. The materials have been characterized by means of Thermogravimetric Analysis (TGA), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and UV-vis Absorption spectroscopy. Irradiation of the materials with white light led to the generation of several bactericidal species, including singlet oxygen (1O2), triiodide anion (I3-) and hydrogen peroxide (H2O2). 1O2 production was demonstrated spectroscopically by reaction with the chemical trap 2,2'-(anthracene-9,10-diylbis(methylene))dimalonic acid (ABDA). In addition, the reaction of iodide anion with 1O2 yielded I3- inside the polymeric matrix. This reaction is accompanied by the formation of H2O2, which diffuses out the polymeric matrix. Generation of both I3- and H2O2 was demonstrated spectroscopically (directly in the case of triiodide by the absorption at 360 nm and indirectly for H2O2 using the xylenol orange test). A series of photodynamic inactivation assays were conducted with the synthesized polymers against Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa. Complete eradication (7 log10 CFU/mL) of both bacteria occurred after only 5 min of white light irradiation (400-700 nm; total energy dose 24 J/cm2) of the polymer containing both RB and TBAI. The control polymer without embedded iodide (only RB) showed only marginal reductions of ca. 0.5 log10 CFU/mL. The main novelty of the present investigation is the generation of three bactericidal species (1O2, I3- and H2O2) at the same time using a single polymeric material containing all the elements needed to produce such a bactericidal cocktail, although the most relevant antimicrobial activity is shown by H2O2. This experimental approach avoids multistep protocols involving a final step of addition of I-, as described previously for other assays in solution.

Bismuth Complex Controlled Morphology Evolution and CuSCN-Induced Transport Improvement Enable Efficient BiI3 Solar Cells.

Bismuth triiodide (BiI3) is a particularly promising absorber material for inorganic thin-film solar cells due to its merits of nontoxicity and low cost. However, one key factor that limits the efficiency of BiI3 solar cells is the film morphology, which is strongly correlated with the trap states of the BiI3 film. Herein, we report a coordination engineering strategy by using Lewis base dimethyl sulfoxide (DMSO) to induce the formation of a stable BiI3(DMSO)2 complex for controlling the morphology of BiI3 films. Density functional theory calculations further provide a theoretical framework for understanding the interaction of the BiI3(DMSO)2 complex with BiI3. The obtained BiI3(DMSO)2 complex could assist the fabrication of highly uniform and pinhole-free films with preferred crystallographic orientation. This high-quality film enables reduced trap densities, a suppressed charge recombination, and improved carrier mobility. In addition, the use of copper(I) thiocyanate (CuSCN) as a hole transport layer improves the charge transport, enabling the realization of solar cells with a record power conversion efficiency of 1.80% and a champion fill factor of 51.5%. Our work deepens the insights into controlling the morphology of BiI3 thin films through the coordination engineering strategy and paves the way toward further improving the photovoltaic performances of BiI3 solar cells.