Research On Preparation And Performance Of High-efficient Perovskite Solar Cells

Organic-inorganic lead halide perovskite solar cells(PSCs)are emerging as promising candidates for the third-generation photovoltaic technology due to its high theoretical conversion efficiency,low-cost,flexible fabrication and etc.During the past several years,although the power conversion efficiency(PCE)of PSCs keep making breakthroughs,and its latest record-certified efficiency is as high as 25.5%,there is still huge room for improvement compared with its theoretical Shockley-Queisser limit efficiency(>30%).Moreover,the long-term stability of PSCs seriously hinders its further development and large-scale commercial application.Therefore,under the premise of ensuring high efficiency,improving the long-term stability of PSCs is a key scientific issue that needs to be broken.It has been extensively demonstrated that the defects at the grain boundaries and interfaces of the perovskite film are the principal factors restricting the further improvement of the photovoltaic performance and stability of PSCs,and the interface passivation engineering is considered to be one of the most valid tactics to solve the above issues.In view of this,this dissertation concentrates on the constitution of multiple interface passivation engineering to minimize the defects of the perovskite film,thereby preparing efficient and stable PSCs.The specific research contents are as follows:(1)A low-cost n-type goethite quantum dots(Fe OOH QDs)synthesized by one-step at room temperature,as a multifunctional interface passivator,has been introduced into the perovskite light-absorber layer to prepare efficient and stable PSCs.Studies found that Fe OOH QDs have dual characteristics of Lewis acid and alkali,and thus can simultaneously coordinate with the cations and anions of perovskite.Therefore,Fe OOH QDs can not only passivate defects by regulating the nucleation and growth of perovskite crystals to reduce grain boundaries and coordinating the under-coordinated cations and anions of perovskite,but also can inhibit the ion migration by virtue of the above coordination effect.As a result,the PSCs with Fe OOH QDs obtained a significant efficiency enhancement from 17.2%to 19.7%,with obviously decreased device hysteresis.Devices show excellent long-term stability,retaining about 97%of the initial power conversion efficiency after 60 d storage in dry air,and preserving up to92%of their initial efficiency under continuous full-sun illumination with maximum power-point tracking for 480 h.Most strikingly,the thermal stability of PSCs with Fe OOH QDs has been significantly enhanced,which maintains 94%of initial efficiency after 360 h at 85 ?.(2)Nitrogen and sulfur co-doped graphene quantum dots(NSGQDs)was hydrothermally synthesized by using citric acid and thiourea as precursors and introduced into perovskite light-absorber layer and its corresponding charge contact interfaces to construct multiple interface passivation engineering,"killed three birds with one stone"has been realized.First,adding an appropriate amount of NSGQDs to the perovskite precursor can not only increase the grain size of the perovskite by reducing the crystallization process,but also passivate defects of perovskite by coordinating the under-coordinated Pb²⁺.Second,the introduction of NSGQDs into the electron contact interface of perovskite layer can reduce the carriers recombination of interface and promote the extraction and injection of electrons.Third,when NSGQDs was introduced into the hole contact interface of perovskite layer,the band alignment of perovskite-hole transport layer interface is optimized,and facilitating the transfer and separation of charges,and ion diffusion of iodide from the perovskite layer to the gold electrode is suppressed.As a result,the PSCs with NSGQDs showed significant efficiency enhancement from 14%to 19.2%(an increase of 37%),which created a new record of the PCE for Fe₂O₃-based PSCs to date.Simultaneously,the device exhibits outstanding humidity,UV light and thermal stability.Furthermore,this strategy is also versatile,and in addition to the Fe₂O₃,was effective at improving the performance of PSCs fabricated with TiO₂ and SnO₂ electron transport materials.(3)A crosslinkable organic small molecule thioctic acid(TA),which simultaneously be chemically anchored to the surface of TiO₂ and methylammonium lead iodide(MAPbI₃)through coordination effects and then in situ crosslinked to form a robust continuous polymer(Poly(TA))network after thermal treatment,be introduced into PSCs to construct multiple interface passivation engineering for greatly passivating the defects.The usage of Poly(TA)has four advantages for achieving the high-performance PSCs.First,an ultrathin Poly(TA)layer is deposited on the TiO₂mesoporous layer,which can passivate the defects at the TiO₂/perovskite interface and thus reduce interfacial recombination;Second,when Poly(TA)is added into the perovskite layer,perovskite grain size can be increased by slowing down the crystallization process and also the perovskite trap states can be obviously passivated via the lewis acid-base reaction.Third,the improved matching of energy levels can accelerate the charge transfer at the perovskite-charge transport layer interfaces.Fourth,the hydrophobic Poly(TA)at PTLIs contributes to the improved water-resisting and light-resisting properties of perovskite film.As a result,Poly(TA)based PSCs achieved PCE of 20.4%with the negligible hysteresis.Devices show excellent long-term stability,retaining about 98%of the initial PCE under highly UV illumination for 450 min,maintaining about 93%of its initial PEC in air with humility of 40±10%for 1440hours,preserving up to 92%of its initial PEC under continuous sunlight illumination with maximum power-point tracking for 600 hours.The density functional theory calculations reveal that-COOH and-C-S functional groups of Poly(TA)interact with under-coordinated Pb²⁺in MAPb I₃ and Ti⁴⁺in TiO₂,confirmed by experimental characterization,in the key in achieving high-performance PSCs herein.