Regulated Crystallization of Efficient and Stable Tin-Based Perovskite Solar Cells via a Self-Sealing Polymer

Abstract

Tin-based perovskite solar cells (PVSCs) have emerged as the most promising lead-free perovskite materials owing to their superior optoelectronic properties. However, the deficiency of accurate control of the tin-based perovskite crystallization process increases the possibility of unexpected perovskite film morphology and defects, resulting in inferior power conversion efficiency (PCE). Meanwhile, the poor environmental stability of tin-based perovskite films hinders its further development. In this work, a unique polymer [poly(ethylene-co-vinyl acetate) (EVA)] is introduced into anti-solvent during spin coating of formamidinium tin tri-iodide (FASnI 3 ) precursor solution. The CO groups contained in EVA have a powerful Lewis acid−base complexation with uncoordinated tin atoms in perovskite grains, which can greatly improve the grain size, optimize the grain orientation, and decrease the surface defects of FASnI 3 films. This strategy offers an impressive PCE of 7.72% with favorable reproducibility. More importantly, the PVSC devices based on FASnI 3 −EVA absorbers have a self-encapsulation effect, which exhibits distinguished moisture and oxygen barrier property, thereby retaining 62.4% of the original efficiency value after aging for 48 h in the air with a humidity of 60%. Such a convenient strategy provides a new inspiration for the establishment of stable and high-performance tin-based PVSCs.

Suppression of Nonradiative Recombination by Vacuum‐Assisted Process for Efficient Lead‐Free Tin Perovskite Solar Cells

“…Three voltage‐dependent regions such as Ohmic region, trap‐filled limit region, and SCLC region can be distinguished from SCLC measurements. [ 54 ] We estimated the trap density by employing the equation, N trap = , where N trap , V TFL , ε r , ε 0 , and L are the trap density, the trap‐filled limit voltage, the relative dielectric constant, the vacuum permittivity, and the thickness of the film, respectively. [ 55 ] As a result, the trap density (3.982 × 10 15 cm −3 ) in vacuum‐treated device is lower than that (6.195 × 10 15 cm −3 ) in untreated one, confirming reduction of hole trap density beneficial to the enhancement of V OC .…”

Additive Engineering toward High‐Performance Tin Perovskite Solar Cells

“…Similarly, Chen et al introduced a Lewis base polymer, poly(ethylene‐ co ‐vinyl acetate) (EVA), to modulate the nucleation process and growth orientation of FASnI 3 perovskite. [ 103 ] The CO groups of EVA enable a powerful Lewis acid–base complexation with Sn 2+ at the grain boundaries of perovskite crystal, enlarging the grain domains with an average size increasing from 196 to 347 nm and decreasing the surface defects of FASnI 3 film, which enhanced the device PCE by 47.6%. Also, the self‐encapsulation effect of EVA effectively blocks the permeation of outside oxygen and moisture into perovskite lattice.…”

Role and Contribution of Polymeric Additives in Perovskite Solar Cells: Crystal Growth Templates and Grain Boundary Passivators

“…Recently, a unique polymer [poly(ethylene‐ co ‐vinyl acetate) (EVA)] was added to an antisolvent during the spin coating of an FASnI 3 precursor solution. [ 157 ] The EVA CO groups contained a powerful Lewis acid–base complexation with uncoordinated tin atoms in perovskite grains, which greatly improved the grain size, optimized the grain orientation, and decreased the surface defects of the FASnI 3 films. This strategy offered an impressive PCE of 7.72% and favorable reproducibility.…”