Polymer Cross-linking Strategy For Efficient And Stable Flexible Perovskite Solar Cells

Recently,perovskite solar cells(PVSCs)have gradually become the most promising of burgeoning photovoltaic power generation technology owing to their excellent photoelectric properties,and the certified power conversion efficiency(PCE)has exceeded 25% which possess a great potential for commercialization.With the fast growth of science technique,the demand for portable wearable devices has increased dramatically.This also motivates people to investigate novel materials and device structures to realize the development and application of high-performance flexible PVSCs(F-PVSCs).However,the inevitable residual strains and lattice mismatch in the commonly prepared perovskite films greatly limit the performance of flexible PVSCs.In addition,the presence of a large number of charge trap states at interface and grain boundaries(GBs)can severely restrain the charge carrier transportation.And the GBs are the major channels for ion transport and water-oxygen penetration,further prompting the deterioration and corrosion of perovskite.All these factors hinder the commercialization development of PVSCs.Therefore,the selection of suitable polymers to anchor or fill the GBs is a feasible tactic to further ameliorate the PCE and stability of the devices.Although multiple polymer additive strategies have been employed to suppress the charge carrier non-radiative combination and enhance the performance of PVSCs,the lack of in-depth studies on the interaction of different functional groups in polymer additives with perovskite may influence the effective selection of passivation molecules.Herein,we systematically incorporate three polymer additives with a similar polymer backbone structure and different functional groups to explore the effect of their interaction energy with perovskite and link it to the photovoltaic performance and stability of the device.Through simulation calculation,it was theoretically verified that different functional groups can modulate the magnitude of the interaction energy between the passivated molecule and the perovskite.Compared with polymethyl acrylate(PMA)and poly(vinyl alcohol)(PVA),poly(acrylic acid)(PAA)exhibits a stronger interaction energy,which contributes to superior passivation effect and reduced defect state density.The PAA-modified PVSCs device achieve a champion PCE of 20.29% accompanied with excellent light soaking stability and thermal stability.And PAA-incorporated F-PVSCs can maintain 75% of the initial PCE after 3000 continuous bending cycles.Furthermore,compared to other semiconductor materials,perovskites have the advantages of excellent flexibility,light weight,and inexpensive,which meet the needs of the flexible optoelectronics field.However,compared to rigid devices,the perovskite interior and buried-bottom interfaces in F-PVSCs may have more inherent defects.In addition,the deformation-induced ductile fracture severely restricts the photoelectric performance and longevity of F-PVSCs.Here,we propose a toughening strategy for low-temperature self-healing perovskite and buried interface through natural small molecule α-lipoic acid(LA),in which LA can autonomously ring-opening polymerization through dynamic covalent disulfide bonds,concurrently form noncovalent hydrogen bonds and coordination bonds to interact with perovskite component.More importantly,the polymerization product Poly(LA)can serve as efficacious passivating and toughening agents to simultaneously optimize the interfacial contact of perovskite/nickel oxide,enhances crystallinity of perovskite films,and sustain device’s mechanical bendability.Subsequently,the best device realizes a champion efficiency up to 21.58% with prominent operational stability.Moreover,the dual effect of dynamic breaking-reorganization of disulfide bonds and facile hydrogen bonds endow cracks of perovskite with self-healability,allowing the devices degraded by repeated deformations to recover to about 95% of the initial efficiency.This toughening and self-healing strategy provides a facile and efficient path to further stabilize flexible devices.