Study On Crystallization Control Of Flexible Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells(PVSCs)have become the most promising photovoltaic technology due to their simple operation process,low cost property,fantastic power conversion efficiency(PCE)and the ability to fabricate large-scale flexible devices.In ten years,the PCE of rigid and flexible devices have exceeded 25%and 19%,respectively.Despite the rising cfficiency of Hexible PVSCs,its long-term stability against moisture,light soaking,and mechanical bending,as well as its film quality under large-scale printing processes,are still the bottlenecks that restrict its further commercial application.In view of the above problems,we aim to comprehensively improve the efficiency and stability of flexible PVSCs through additive engineering,interface engineering,ink engineering,and flexible mechanical structure design from the perspective of the transition from basic research to commercial application.The Inain contents of this dissertation are as follows:(1)Enhancing the nucleation and regulating the crystallization rate of perovskitc flms and improving the bendability of brittle hybrid grains arc crucial to improving the photovoltaic pcrlormance of flexible PVSCs.We incorporate elastomer polyurethane(PU)additive into the perovskite precursor solution to retard the perovskite crystallization rate and improve the device performance.More importantly,the clastomer PU additive crosslinks the grain boundaries between neighboring perovskite crystals to form a PU network that effectively improves the mechanical stability of the perovskite flms.This strategy is expected to be of profound signilcance for the realization of perovskite solar cells as flexible and wearable devices.(2)The two-step deposition technique has been demonstrated as an cfficient,low-cost approach to fabricate large-scale PVSCs.However,these large-scale PVSCs are lagging far behind the state-of-the-art spin-coated counterparts,because of the unstabilized nature or Pbl2 proursor ink and the difficulty in complete conversion to crystallized perovskite films.Here,we demonstrate a stabilized and operational trace methylammonium iodide(MAI)-PU-lead iodide(PbI2)(MP-Pbl2)precursor ink formulation to fabricate large-scale PVSCs via bladc-coating process.The synergetic effects of trace MAI and PU can regulate the rheological properties of PbI2 precursor ink,and form an oriented intermediate complex,which are benefit for constructing compact perovskite films with fewer pinholes and defects.Thus,the MP-PbI2-based PVSCs yield power conversion efficiencies(PCEs)over 19%for a 0.12 cm2 device and 11.07%for a 25 cm2 solar module.Moreover,flexible PVSC with a PCE of 17.30%has been manufactured by using this scalable ink formulation and maintaining over 90%of its original PCE after 6000 bending cycles at the radius of 3 mm.This approach opens up a new precursor engineering for achieving large-scale PVSCs via roll-to-roll technology.(3)The extraordinary photovoltaic performance of PVSCs can be maximized only if an extremely stabili.zed device structure is developed.Here,we introduce a novel glued poly(ethylene-co-vinyl acetate)(EVA)interfacial layer to fabricate highly efficient and stable PVSCs with excellent waterproofness and flexibility.This strategy can effectively passivate perovskite surface,reduce defect density and balance charge transfer,which leads to a champion PCE of 19.31%for a 0.1 cm2 device and 1.73%for a 25 cm2 solar module.More importantly,the formation of a glued EVA thin layer on the surface of perovskite can inhibit ionic migration to the Ag electrode,form favorable interfacial contact and adhesive interaction with the perovskite/PC61BM to sustain mechanical bending,and produce significant waterproofness from moisture invasion,thus facilitating improvement in the operational stability of the PVSCs.The EVA-treated PVSCs exhibit superior PCE values of 15.12%for a flexible device(0.1 cm2)and 8.95%for a flexible module(25 cm2),as well as over 85%retention after 5000 bending cycles,which opens up a new strategy for the practical application of PVSCs in portable and wearable electronics.(4)Perovskite materials hold great potential as photovoltaic power sources for portable devices owing to their dramatic performance.However,the poor long-term stability and mechanical stability require further improvement to attain practical viability.We have investgated the the effect of flexible lamination process on the quality of flexible perovskite film and device performance.Combined with flexible lamination and EVA treatment processes,a flexible PVSC with a PCE of 6.42%is obtained.The resulted flexible PVSCs exhibit excellent waterproof performance owing to self-encapsulation by lamination process and EVA protective layers.In addition,the mechanical properties under extreme deformation have been investigated through these strateges on an ultra-thin substrate.The resulted flexible PVSC can maintain over 95%of its original PCE after 1000 bending cycles at the radius of 0.5 mm.More importantly,this flexible lamination technology can modulate the mechanical neutral plane such that it lies on the perovskite layer,which enabled us to obtain ultra-flexible PVSCs capable of enduring crumpling deformation tests of more than 100 cycles.This ultra-flexible PVSC will provide a new approach for development of wearable electronics.