| Hybrid organic-inorganic perovskite solar cells(PSCs)have attracted great interest over the past years due to their high power conversion efficiency(PCE)exceeding 25%,which is similar to the performance of single crystalline silicon solar cell.However,the chemical instability of organic-inorganic hybrid perovskite halides show low stability under sun illumination and thermal aging conditions hampers their further application owing to the organic components in the hybrid crystal structure.As an alternative,cesium-based all-inorganic perovskites show much better stabilities,which organic cations is substituted by Cs+.CsPbI2Br inorganic perovskite has attracted much attention because of its suitable band gap and high phase stability.The PCEs of CsPbI2Br PSCs rapidly improve to 17.03%,but still below those record of hybrid organic-inorganic perovskite solar cells.Thus,further performance optimization is still important.Considering the interface engineering plays an important role to improve the performance of the device,this work is mainly focused on the interface design between each layer in CsPbI2Br PSCs,aims to optimize device properties and stability.And It mainly includes the following three works(1)In this work,solution-processed two-dimensional Nb2O5(001)nanosheets(c-Nb2O5 NS)were prepared and combined with[6,6]-phenyl-C61-butyric acid methyl ester(PC6iBM)as electron transport layer(ETL)for inverted inorganic CsPbI2Br perovskite solar cells(PSCs).The PSCs with c-Nb2O5/PC61BM bilayer ETL yielded high PCE up to 11.74%with high thermal stability,remarkably outperforming the devices with only PC61BM.Mechanism studies have shown that,compared with PC61BM,the c-Nb2O5/PC61 BM electron transport double-layer can more effectively passivate perovskite surface defects,promote the extraction of photogenerated electrons and prevent hole transport,and effectively inhibit iodine ions to the Ag electrode diffusion.Therefore,this work provides a positive reference for the design of the electron transport layer of the inverted inorganic perovskite solar cell.(2)We designed and optimized a new type of undoped Spiro-OMeTAD/TS-CuPc double-layer hole transport layer(HTL),and applied it to the inverted structure of CsPbI2Br perovskite solar cell.The PCE of the perovskite solar cell based on Spiro-OMeTAD/TS-CuPc reaches 14.85%and shows excellent thermal stability,which is significantly better than that based on a single undoped Spiro-OMeTAD or PEDOT:PSS.A series of physical and device characterization results show that the Spiro-OMeTAD/TS-CuPc hole transport double-layer help the growth of the perovskite layer,and to obtain an excellent film with higher crystallinity,larger grains and lower density of trap states.The hole transport double-layer also helps to improve the energy level arrangement at the hole transport layer/perovskite interface,promote hole transport,and inhibit interface charge recombination.(3)To boost the photovoltaic performance of inorganic PSCs,we designed a facile and efficient strategy of gradient doping is adopted for optimizing the inverted CsPbI2Br PSCs.Particularly,a bicationic iodine salt,namely 2,2’-bis(trifluoromethyl)-[1,1’-biphenyl]-4,4’-diamine iodine(BFBAI2),is used as dopant,which has been proved to be gradient distributed across the perovskite(PVK)and ZnO layers.A series of physical characterization results show that BFBAI2 presents a gradient distribution in both the perovskite layer and the ZnO electron transport layer.As the result,a power conversion efficiency(PCE)of～14.38%can be achieved for the BFBAI2 doped PSCs,with enhanced stability under ambient or thermal aging condition,much surpassing those of pristine devices.The improvements are attributed principally to the follow two factors:i)The gradient doping of BFBAI2 both in the perovskite and ZnO layers significantly passivated interface defects;ii)The gradient doping of BFBAI2 in the perovskite layer leads to the gradient passivation effect and the enhancement of the built-in electric field. |
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