Room‐Temperature Partial Conversion of α‐FAPbI₃Perovskite Phase via PbI₂Solvation Enables High‐Performance Solar Cells

Abstract

The two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI3 hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI3, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI3, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI2 into the α‐FAPbI3 perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI2 precursor from its different states are compared. α‐FAPbI3 forms spontaneously and efficiently at room temperature from P2 (ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI2) to 17.23(±0.28)% (from solvated PbI2) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA+ cation without the need for Cs+ or mixed halide formulation.

Unraveling the compositional heterogeneity and carrier dynamics of alkali cation doped 3D/2D perovskites with improved stability

“…[1][2][3][4][5][6] Substantial efforts have been put into improving device power conversion efficiency (PCE) 7 , which are positively related to perovskite morphology, microstructure, mobility, defect, and trap state density. [8][9][10][11][12][13] To date, planar heterojunction three-dimensional (3D) perovskite photovoltaics fabricated through interfacial engineering have recently surpassed the PCE milestone of 25%. 14 Despite its high efficiency, 3D perovskites are susceptible to the external environment, such as moisture, heat, and irradiation, which leads to phase degradation and hinder the device performance.…”

Precise Control of Perovskite Crystallization Kinetics via Sequential A‐Site Doping

“…The defect densities of different perovskite films are also evaluated by the space‐charge‐limited current (SCLC) measurements with the device structure of FTO/SnO 2 /perovskite/[6,6]‐phenyl‐C 71 ‐butyric acid methyl ester/Au, [ 47 ] as shown in Figure S19 in the Supporting Information. The defect density ( N t ) is determined by the equation of , where ε r is the relative dielectric constant, [ 48 ] ε 0 is the vacuum permittivity, V TFL is the onset voltage of the trap‐filled limit region, q is the elementary charge, and L is the thickness of the film. The defect density of the perovskite films without Cs + , with Cs + , and with Cs + & GA + is calculated to be 1.35 × 10 16 , 7.01 × 10 15 , and 3.10 × 10 15 cm −3 , respectively, which confirms that the perovskite with Cs + & GA + exhibits a reduced defect density.…”

“…, where ε r is the relative dielectric constant, [48] ε 0 is the vacuum permittivity, V TFL is the onset voltage of the trap-filled limit region, q is the elementary charge, and L is the thickness of the film. The defect density of the perovskite films without Cs + , with Cs + , and with Cs + & GA + is calculated to be 1.35 × 10 16 , 7.01 × 10 15 , and 3.10 × 10 15 cm −3 , respectively, which confirms that the perovskite with Cs + & GA + exhibits a reduced defect density.…”

The J–V Hysteresis Behavior and Solutions in Perovskite Solar Cells

“…Among the third-generation solar cells, perovskite solar cells (PSCs) have achieved rapid development in recent years due to their excellent photovoltaic performance, and low cost fabrication process. [1][2][3][4][5] Since the first reported by Kojima et al in 2009, the power conversion efficiency (PCE) of PSCs has rapidly increased from 3.8% to 25.5%. [6][7][8][9] However, PSCs still have some problems that hinder their further development, such as poor long-term stability, the toxicity of lead (Pb) ions and current density-voltage ( J-V ) hysteresis.…”