Structure Design And Performance Enhancement On Cs-based All-Inorganic Perovskite Solar Cells

Limited by the poor stability against environment,organic-inorganic hybrid perovskite solar cells(PSCs)are still facing challenges on the way of commercialization,although they have achieved amazing photovoltaic performance.All-inorganic metal halide perovskite materials have been developed to solve this problem.By substituting the organic cations with cesium cation(Cs+),cesium-based all-inorganic perovskites exhibit stronger thermal stability,faster carrier transport efficiency,larger charge diffusion length and greater open-circuit voltage(Voc)in theory.However,there are also many issues to deal with in the field of inorganic PSCs,for example,instability of the cubic phase,energy loss due to unsuitable device configuration,transport imbalance of electrons and holes,and unclear mechanism of film quality control.In this paper,we aim at overcoming these hurdles through compositional engineering,heterojunction engineering,interface engineering and passivation engineering for the structure modulation and performance enhancement of perovskite films as well as photovoltaic devices.Systematic mechanism model on structural stability and trap-assisted charge recombination has been established.The main research contents are as follows.(1)Fluorine(F)is introduced into the X-site in cubic ABX3 structure of CsPbBrI2 all-inorganic perovskite,forming ?-?-phase heterojunction.We studied the influence of doping ratio on phase stability,optical prepoties and charge transport of CsPbBrI2-xFx films,discovering that the phase hybrid structure not only benefited dissociation of excitons and charge transport,reduced charge recombination and prolonged the lifetime of carriers,but also improved the phae stability of the perovskite film at room temperature under high humidity by modulating the effective tolerance factor towards the empirical stable value of cubic structure.The CsPbBrI1.78F0.22 PSC with optimized?-/?-phase heterostructrue displayed both superior power conversion efficiency(PCE)up to 10.26%and outstanding structural stability against moisture and time.(2)Bismuth telluride(Bi2Te3)nanoplates are designed as an interlayer between CsPbBrI2 perovskite and hole transport material,Spiro-OMeTAD.Confirmed by systematic electrochemical and photoelectrical techniques,Bi2Te3 interlayer was capable of drastically bringing down the notorious trap states and electron-hole recombination,enhancing hole extraction and transport efficiency,and prolonging effective lifetime thanks to the matched band level structure.The all-inorganic PSCs with optimal Bi2Te3 interlayer exhibited larger photocurrent density and less open circuit voltage loss,leading to greatly enhanced PCE.Besides,Bi2Te3 also acted as a blocking layer for both the migration of iodide ions,silver and moisture,resulting in considerable long-term stability without extra encapsulation.(3)We employed eco-friendly,earth-abundant and cost-effective antimony selenide(Sb2Se3)in the p-n heterojunction combined with CsPbBrI2,developing a complete inorganic device structure.To heal Se vacancy defects formed during the thermal evaporation,post-selenization was applied and successfully reducied energy loss of charge recombination.In the meantime,carefully modulated Sb2Se3 draged down its Fermi level and reinforced built-in electric field,therefore enhancing the driving force of carrier transport.The light harvesting range of the whole device was broadened since the narrower band gap of Sb2Se3 compared with CsPbBrI2.Moreover,in the presence of hydrophobic Sb2Se3,ions migration was removed and nearly 80%of the initial efficiency was kept without encapsulation after 60 days.This all-inorganic p-n heterojunction solar cell achieved a PCE exceeding 9%after optimation.(4)Serving as passivation additive,Cu2ZnSnS4(CZTS)quantum dots were added into the CsPbBrI2 perovskite film.The crystallization process of inorganic perovskite was adjusted for the heterogeneous nucleation sites provided by CZTS quantum dots,leading to dense film morphology with less grain boundary defects.The passivation effect decreased trap state density,thus making the perovskite film with lower nonradiative charge recombination rate and better photoelectric property.The all-inorganic planar PSC modified by CZTS quantum dots enlarged the VOC from 0.96 to 1.12 V,and PCE from 8.70%to 11.96%.