Crystallization Regulation And Stability Study Of Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells(PVSCs)have good marketability and commercial prospects due to its excellent photovoltaic performance and low-cost process.After intensive research over the past decade,the champion PVSCs have successfully achieved certified power conversion efficiency(PCE)of25.5%,which makes it comparable to the silicon-based solar cells.However,the PVSCs is difficult to be used commercially on a large scale due to the instability of perovskite under external conditions such as water,oxygen,heat and light conditions and the toxicity of conventional lead-based.The crystallization of perovskite film plays a crucial role in PCE and stability of PVSCs.High-quality perovskite film can not only ensure sufficient light capture,but also reduce carrier recombination,enhance charge transport inside the device,thereby improving the photovoltaic performance of PVSCs.In addition,the interfacial charge transfer material is also an important impact on the device performance.However,the preparation of high-quality perovskite film and the development of excellent interfacial electron transport material for PVSCs remain a great challenge.In this paper,we have regulated the morphology,intrinsic hydrophobicity,interfacial lattice strain and interfacial reaction of perovskite film by additive and interfacial engineering in order to improve the efficiency and stability of PVSCs.Tin-based perovskites with narrow bandgaps and high charge-carrier mobilities are promising candidates for the preparation of efficient lead-free PVSCs.However,the deficiency of accurate control for 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 film 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(FASn I₃)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 grain size,optimize grain orientation and decrease surface defects of FASn I₃films.This strategy offers an impressive PCE of 7.72%with favorable reproducibility.More importantly,the PVSCs devices based on FASn I₃-EVA absorber 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 air environment with humidity of 60%.Such convenient strategy provides a new inspiration for the establishment of stable and high performance tin-based PVSCs.Zinc oxide(ZnO)is expected to be the desirable electron transport layer(ETL)for planar perovskite solar cells(PVSCs)because of excellent electron mobility,superior transmittance in the visible spectrum and aligned energy level with perovskite.However,the development of ZnO-based PVSCs is relatively stagnant,mainly due to interfacial mismatch and deprotonation.Herein,aluminium-doped ZnO modified by polydopamine(AZO:PDA)as ETL has firstly been found to optimize interfacial contact and inhibit detrimental interfacial reaction.The surface defects of AZO:PDA has been effectively passivated to mitigate the non-radiative carriers recombination.Moreover,various functional hydroxyl and amino groups from AZO:PDA can not only induce the vertical growth of perovskite grains,but also release the lattice strain and inhibit the deprotonation reaction.Consequently,the rigid device(ITO/AZO:PDA/FA_0.9Cs_0.1Pb I₃/Spiro-OMe TAD/Ag)shows a champion power conversion efficiency(PCE)of 21.36%with small hysteresis effect.The unencapsulated devices can preserve 90%and 88%of their initial efficiencies after storing at 85°C for 360 h and continuous light for 500 h,respectively.In addition,a PCE of 18.51%is achieved in flexible device due to the advantages of bendability and interfacial adhesion from AZO:PDA,which is one of the highest PCEs recorded among ZnO-based flexible PVSCs.