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First-principles calculations were conducted to examine the impact of three sulfonamide-containing molecules (H4N2O2S, CH8N4O3S, and C2H2N6O4S) adsorbed on the FAPbI3(001) perovskite surface, aiming to establish a significant positive correlation between the molecular structures and their regulatory effects on the perovskite surface. A systematic comparison was conducted to evaluate the adsorption stability of the three molecules on the two distinct surface terminations. The results show that all three molecules exhibit strong adsorption on the FAPbI3(001) surface, with C2H12N6O4S demonstrating the most favorable binding stability due to its extended frameworks and multiple electron-donating/withdrawing groups. Simpler molecules lacking carbon skeletons exhibit weaker adsorption and less dependence on surface termination. Ab initio molecular dynamics simulations (AIMD) further corroborated the thermal stability of the stable adsorption configurations at elevated temperatures. Electronic structure analysis reveals that molecular adsorption significantly reconstructs the density of states (DOS) on the PbI2-terminated surface, inducing shifts in band-edge states and enhancing energy-level coupling between molecular orbitals and surface states. In contrast, the FAI-terminated surface shows weaker interactions. Charge density difference (CDD) analysis indicates that the molecules form multiple coordination bonds (e.g., Pb–O, Pb–S, and Pb–N) with uncoordinated Pb atoms, facilitated by –SO2–NH2 groups. Bader charge and work function analyses indicate that the PbI2-terminated surface exhibits more pronounced electronic coupling and interfacial charge transfer. The C2H12N6O4S adsorption system demonstrates the most substantial reduction in work function. Optical property calculations show a distinct red-shift in the absorption edge along both the XX and YY directions for all adsorption systems, accompanied by enhanced absorption intensity and broadened spectral range. These findings suggest that sulfonamide-containing molecules, particularly C2H12N6O4S with extended carbon skeletons, can effectively stabilize the perovskite interface, optimize charge transport pathways, and enhance light-harvesting performance.

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. A combined method is proposed by introducing 3,4,5‐Trifluoroaniline iodide (TFAI) into the perovskite precursor. The TFAI induces a complete phase transition of α‐FAPbI3 at room temperature and serves as a passivation agent at grain boundaries. The TFAI‐modified device achieves over 24% PCE and maintains steady power output for 380 h with almost no performance decay.

High temperatures facilitate the formation of stable, high‐crystallinity α‐FAPbI3 films but can lead to the volatilization of organic components in perovskites. Here, a 300 °C hot‐press‐assisted recrystallization strategy is reported to grow stable phase‐pure α‐FAPbI3 film without any dopants. High temperature can promote the transformation of δ‐FAPbI3 to α‐FAPbI3, and induces recrystallization to relieve strain. The applied pressure creates a confined space that effectively prevents the volatilization of organic components in perovskite. The α‐FAPbI3 film prepared by hot‐press at 300 °C achieves an average grain size of ≈3 µm (with grains up to 10 µm) and demonstrates excellent damp‐heat stability, showing no significant change after 20 s in deionized water. The result solar cell delivers a power conversion efficiency as high as 24.06% and retains >70% of their initial efficiency value after 1000 h at 85 °C and 85% relative humidity. Phase‐pure dopant‐free α‐FAPbI3 perovskite films are being prepared by hot‐press assisted annealing at 300 °C. Higher temperature can promote the transformation of δ‐FAPbI3 to α‐FAPbI3, induce recrystallization to relieve strain. The applied pressure creates a confined space that effectively prevents the volatilization of organic components in perovskite. The result solar cell achieves a PCE of 24.06% and demonstrates ultra‐high damp‐heat stability.

Highlights A lattice-anchoring strategy using low-dimensional perovskite addresses structural instability in α-formamidinium lead iodide (FAPbI 3 ) by matching crystal lattice, mitigating residual stress and tensile strain. Enhanced Pb-I bonding strength and reduced lattice strain improve structural stability and carrier mobility-lifetime product, enabling efficient charge transport. Optimized X-ray detectors achieve high sensitivity (1.83 × 10 5 μC Gy air –1 cm –2 ), low detection limit (27.6 nGy air s –1 ), and stable performance under prolonged irradiation. Formamidinium lead iodide (FAPbI 3 ) perovskite exhibits an impressive X-ray absorption coefficient and a large carrier mobility-lifetime product (µτ), making it as a highly promising candidate for X-ray detection application. However, the presence of larger FA + cation induces to an expansion of the Pb-I octahedral framework, which unfortunately affects both the stability and charge carrier mobility of the corresponding devices. To address this challenge, we develop a novel low-dimensional (HtrzT)PbI 3 perovskite featuring a conjugated organic cation (1H-1,2,4-Triazole-3-thiol, HtrzT + ) which matches well with the α-FAPbI 3 lattices in two-dimensional plane. Benefiting from the matched lattice between (HtrzT)PbI 3 and α-FAPbI 3 , the anchored lattice enhances the Pb-I bond strength and effectively mitigates the inherent tensile strain of the α-FAPbI 3 crystal lattice. The X-ray detector based on (HtrzT)PbI 3 (1.0)/FAPbI 3 device achieves a remarkable sensitivity up to 1.83 × 10 5 μC Gy air −1  cm −2 , along with a low detection limit of 27.6 nGy air s −1 , attributed to the release of residual stress, and the enhancement in carrier mobility-lifetime product. Furthermore, the detector exhibits outstanding stability under X-ray irradiation with tolerating doses equivalent to nearly 1.17 × 10 6 chest imaging doses.

FAPbI3(NH2CHNH2PbI3) is an organic-inorganic hybrid perovskite containing Pb, which has good photoelectric characteristics and great potential in the application of low-cost and high energy efficiency photoelectric devices. In order to reduce the pollution of Pb to the environment, the first-principles based on density functional theory(DFT) is used to compare and study the photoelectric parameters such as the band structure, density of states(DOS), absorption coefficient, reflectivity, conductivity and dielectric function of FAPb1−xGexI3(x = 0.0,0.33,0.50,0.67,1.0). The results show that the 4p orbital electrons of Ge and the 6p orbital electrons of Pb and 5p orbital electrons of I are hybridized after doped with Ge, which change the band structure of FAPbI3. The result is that the optical band gap of the material is narrowed, the curvature of the band is increased, the effective mass of electrons and holes is reduced, the absorption peak of visible light increases and the absorption range increases. And the reflectivity and energy loss of the material also increase at the same time. The super SOC effect of the heavy metal Pb element leads to the splitting of the conduction band level of FAPbI3, the conduction band value drops sharply, and the band gap decreases sharply. We found that when the doping ratio of x in FAPb1−xGexI3 was between 0.55 and 0.65, the optimal band gap was between 1.3–1.4 eV. Therefore, reasonable regulation of Ge’s doping ratio can improve the photoelectric conversion efficiency of FAPbI3. This study can provide some theoretical guidance for experimental research and search for new efficient and environmentally friendly perovskite solar materials.

A thorough investigation of perovskite structures formed through doping is essential for advancing the efficiency and stability of perovskite solar cells. In this study, Bi-doped FAPbI 3 perovskite films with varying Bi concentrations (0.5–2%) were fabricated using a spin-coating technique on ITO glass substrates. Then the films’ phase structure, local structure, and optical characteristics were analyzed. X-ray diffraction (XRD) analysis revealed that the pristine FAPbI 3 film exhibited both hexagonal and cubic phases, indicating structural instability. In contrast, Bi-doped FAPbI 3 films predominantly displayed a cubic perovskite structure, with a notable reduction in the XRD peak intensity corresponding to the hexagonal phase. UV–Vis spectroscopy showed that the undoped FAPbI 3 film had an absorption edge in the visible-near infrared range, while Bi-doping caused a redshift, indicating a reduction in the optical band gap. The calculated results show that optical band gaps decrease with increasing Bi, from a value of 1.49 (pure) to 1.43 (2% Bi) eV. X-ray absorption near edge structure (XANES) analysis confirmed the oxidation states of Pb 2+ and Bi 3+ ions across all samples, with Bi ions replacing Pb in the local structure. Photoluminescence (PL) measurements revealed an increased PL intensity with 1% Bi doping (7 10 5 ) compared with pristine FAPbI 3 (4.7 10 5 ), suggesting a reduction in carrier recombination. These findings demonstrate the potential of Bi-doping to stabilize perovskite structures with improved optoelectronic properties.

Density functional theory calculations have been performed to study the effect of replacing lead by alkaline earth metals on the stability, electronic and optical properties of the formamidinium lead triiodide (FAPbI3) (111) and (100) surfaces with different terminations in the form of FAPb1-xAExI3 structures, where AE is Be, Mg or Ca. It is revealed that the (111) surface is more stable, indicating metallic characteristics. The (100) surfaces exhibit a suitable bandgap of around 1.309 and 1.623 eV for PbI5 and PbI6 terminations, respectively. Increases in the bandgaps as a result of Mg- and Ca-doping of the (100) surface were particularly noted in FAPb0.96Ca0.04I3 and FAPb0.8Ca0.2I3 with bandgaps of 1.459 and 1.468 eV, respectively. In the presence of Be, the band gap reduces critically by about 0.315 eV in the FAPb0.95Be0.05I3 structure, while increasing by 0.096 eV in FAPb0.96Be0.04I3. Optimal absorption, high extinction coefficient and light harvesting efficiency were achieved for plain and doped (100) surfaces in the visible and near UV regions. In order to improve the optical properties of the (111)-PbI3 surface in initial visible areas, we suggest calcium-doping in this surface to produce FAPb0.96Ca0.04I3, FAPb0.92Ca0.08I3, and FAPb0.88Ca0.12I3 structures.

The highly oriented 2D perovskite templates of n = 1 have typically been created to attain controllable and oriented crystallization of 3D α‐phase formamidinium lead triiodide (α‐FAPbI3) perovskites. However, the role of methylammonium iodide (MAI), a widely used α‐FAPbI3 phase stabilizer, in regulating the growth dynamics of 2D/3D perovskites is generally ignored. Herein, Ruddlesden–Popper type n = 1 2D octylammonium lead iodide (OA2PbI4) perovskites are added into FAPbI3 precursor solution. The template of n = 2 (OA2MAPb2I7), which is spontaneously constructed by the mixture of n = 1 2D and methylammonium chloride (MACl), acts as a skeleton to template the epitaxial growth of α‐FAPbI3. However, the volatilization of MACl inevitably causes damage to the 2D structure during thermal annealing. This study reveals that small amounts of less volatile MAI additive enables the creation of stable 2D template, leading to more controlled vertical orientation crystallization. Consequently, the high‐quality mixed‐dimensional perovskite film delivers a high efficiency of 24.19% together with improved intrinsic stability. This work provides an in‐depth understanding of 2D‐assisted controlled epitaxial growth of α‐FAPbI3. MAI dopants are commonly introduced in 2D/3D hybrid perovskites to stabilize the crystal structure of α‐FAPbI3, while the role of MAI in regulating the growth dynamics of α‐FAPbI3 is generally ignored. It reveals that small amounts of MAI make the 2D template more stable, leading to controlled crystallization and a strong degree of preferential orientation for α‐FAPbI3 perovskites.

Germanium (Ge) was added to formamidinium cesium lead triiodide perovskite crystals and the microstructures and photovoltaic properties were investigated. The Ge addition stabilized the α-phase of the perovskites and suppressed formation of the δ-phase. X-ray diffraction peaks of the α-phase increased by increasing the Ge contents. The highest conversion efficiency of 6.05% was obtained for the 12.5% Ge added device in an air atmosphere and the increase of efficiencies would be due to the promoted formation of photoactive α-formamidinium cesium lead triiodide perovskite crystals.

Typically n-i-p structured perovskite solar cells (PSCs) incorporate 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenyl amine)-9,9′-spirobifluorene (spiro-OMeTAD) as the hole-transporting material. Chemical doping of spiro-OMeTAD involves a lithium bis(trifluoromethyl sulfonyl)imide dopant, causing complex side-reactions that affect the device performance, which are not fully understood. Here, we investigate the aging-dependent device performance of widely used formamidinium lead triiodide (FAPbI3)-based PSCs correlated with lithium-ion (Li+) migration. Comprehensive analyses reveal that Li+ ions migrate from spiro-OMeTAD to perovskite, SnO2, and their interfaces to induce the phase-back conversion of α-FAPbI3 to δ-FAPbI3, generation and migration of iodine defects, and de-doping of spiro-OMeTAD. The rapid performance drop of FAPbI3-based PSCs, even aging under dark conditions, is attributed to a series of these processes. This study identifies the hidden side effects of Li+ ion migration in FAPbI3-based PSCs that can guide further work to maximize the operational stability of PSCs.