The Study Of Active Layer Modulation And Transparentization Processing For Wide-bandgap Perovskite Solar Cells

Recently,perovskite materials have drawn much attention from researchers due to their excellent photoelectric properties and tunable bandgap.The best certified power conversion efficiency（PCE）of single-junction perovskite solar cells（PSCs）has been achieved 26.0%.For breaking up efficiency limit of single-junction solar cells and im-proving the PCE of solar cells,an ideal solution is to fabricate perovskite-based tandem solar cells.As top light absorption layers,wide-bandgap perovskites（range of bandgap:1.55～2.30 e V）are an important component of tandem solar cells.Up to now,two-junction and triple-junction tandem solar cells are the most representative tandem solar cells.For triple-junction tandem solar cells,all bromide-based perovskites（bandgap of≈2.3 e V）are appropriate choices.Due to the non-radiative carrier recombinations in the bulk and at the interface of the perovskite,the PCEs of all-bromide-based PSCs are still low,leaving large room for efficiency improvement.To solve the problem of per-ovskite thin film in all-bromide-based PSCs,this dissertation used thin film optimiza-tion strategy to improve the PCE of all-bromide-based PSCs through organic salt post-treatment method（the first work）and additive method（the second work）.For two-junction tandem solar cells,wide-bandgap perovskites（bandgap of≈1.7 e V）are ideal materials.During the preparation of semitransparent（ST）wide-bandgap PSCs for tan-dem application,sputtered transparent electrodes cause sputter damage and nonideal contact between electrodes and carrier transport layers,resulting in performance dete-rioration of devices.To solve the problem of transparentization processing for wide-bandgap PSCs,this dissertation used buffer layer optimization strategy to reduce nega-tive effects of sputtered transparent electrodes on ST-PSCs via design of buffer layers（the third work）and selection of buffer layers（the fourth work）.This dissertation lays the foundation for further research of efficient two-junction or triple-junction tandem solar cells.The specific research contents are shown in the following:1.Optimizing perovskite thin film to improve the performance of normal all-bro-mide-based PSCs.Inorganic Cs Pb Br₃ perovskite has huge advantage in stability.How-ever,non-radiative carrier recombinations in the bulk and at the interface of the perov-skite degrade the performance of Cs Pb Br₃ PSCs.To solve the problems of perovskite thin film,we studied the effect of organic salt FABr post-treatment on Cs Pb Br₃ thin film.After FABr post-treatment,ion exchange between FA⁺and Cs⁺changed energy-level structure of perovskite thin film,reduced valence bandgap maximum energy-level difference between perovskite and Spiro-OMe TAD on the Spiro-OMe TAD side,formed additional electric field on the Sn O₂ side,facilitating the extraction of carrier.In addition,this method passivated defects at grain boundaries and surface of perovskite thin film,reducing the defect-related non-radiative recombination.After FABr post-treatment,the PCE of normal Cs Pb Br₃ PSC was improved from 6.74%to 8.25%.After1000 h of storage stability test（or 720 h of thermal stability test at 85^oC）,the PCEs of control and FABr-treated devices maintained over 90%of their initial values,indicating excellent stability of control and FABr-treated Cs Pb Br₃ film.2.Optimizing perovskite thin film to improve the performance of inverted all-bro-mide-based PSCs.FAPb Br₃ perovskite has advantages of good stability and low prep-aration temperature.However,defects generated during the deposition of FAPb Br₃ thin film lead to non-radiative carrier recombinations in the bulk and at the interface of the perovskite.To solve the problem of perovskite thin film,we studied the effects of FAAc additive on perovskite thin film.FAAc passivated the defects in FAPb Br₃ thin film,reducing defects-related non-radiative recombination.Besides,introduction of FAAc reduced surface roughness of FAPb Br₃ thin film,benefiting for the improvement of fill factor（FF）.FAAc additive improved the PCE of inverted FAPb Br₃ PSC from 5.30%to6.74%.After 864 h of storage stability test,the PCEs of control and FAAc-added de-vices maintained over 80%of their initial values.After 624 h of thermal stability test at85^oC,the PCE of FAAc-added device maintained 37.9%of its initial value,while the PCE of the control device maintained 27.6%of its initial value.3.Optimizing buffer to improve the performance of inverted ST wide-bandgap PSCs.ST wide-bandgap PSC（≈1.7 e V）is currently a key research direction because of its application in two-junction perovskite/silicon tandem solar cells.During the prep-aration of ST-PSCs,top transparent electrodes deposited by magnetron sputtering will cause problems.On one hand,high-energy particles generated during sputtering process damage as-prepared functional layers.On the other hand,transparent electrodes form nonideal contact with carrier transport layer.To solve these problems related to trans-parentization processing of PSCs,we studied the effect of multi-layer buffer on the performance of inverted ST-PSCs.The optimized PCE of inverted wide-bandgap PSCs achieved 20.06%.Based on this kind of PSCs,ST wide-bandgap PSCs with Zn O,Zn O/BCP or Zn O/BCP/Ag as buffer were fabricated.Comparing with Zn O buffer and Zn O/BCP buffer,Zn O/BCP/Ag multi-layer buffer reduced the contact resistance be-tween transparent electrode and electron transport layer,facilitating carrier transport at interface.In addition,Zn O/BCP/Ag multi-layer buffer reduced non-radiative recombi-nation at the interface of transparent electrodes and electron transport layer.The appli-cation of multi-layer buffer improved the PCE of inverted ST wide-bandgap PSC from7.88%to 16.14%.By evaporating Ag electrode along the edge of transparent electrode,the PCE of ST-PSC was increased to 17.95%.The PCE of four-terminal perovskite/sil-icon tandem cell containing an inverted ST wide-bandgap PSC（17.95%）and a silicon cell（22.57%）is 26.18%.4.Optimizing buffer to improve the performance of normal ST wide-bandgap PSCs.In normal ST-PSCs,Mo O_x buffer not only absorbs near-infrared light but also reacts with perovskite.To solve the problems related to Mo O_x buffer,we studied the effect of different buffer layer on the performance of normal ST-PSCs.The optimized PCE of normal wide-bandgap PSCs achieved 18.15%.Based on this kind of PSCs,ST-PSCs with Mo O_x and Ni O_x buffer were fabricated.Compared with Mo O_x buffer,Ni O_xbuffer reduced contact resistance between hole transport layer and transparent electrode,accelerating the extraction of carrier.Compared to ST-PSC with Mo O_x as buffer（PCE:10.27%）,ST-PSC with Ni O_x buffer exhibited higher efficiency（PCE:13.13%）and transmittance（≈3%enhancement in the range of 800 to 1200 nm）,proving the feasi-bility of Ni O_x buffer layer.