The Fabrication Of Electron Transportation Layer And Improvement Of Perovskite Film In Perovskite Solar Cells

Hybrid organic-inorganic perovskite solar cells?Pero-SCs?have attracted plenty of attention due to the merits of high power conversion efficiency?PCE?,solution-processability and low fabrication costing and so on.The PCE of the best Pero-SC is as high as 22.1%so far.It is predicated that Pero-SC will be commercialized in years,and that is a promising substitute of the expensive silicon-based solar cells.The development of new perovskite materials,synthesis of interlayer materials with high charge transport properties,fabrication of new type device architectures and enhancement of the quality of perovskite films have been the research focuses in the field of Pero-SCs.In this paper,in order to enhance the device performances of Pero-SCs,we selected the materials and optimized of processes of electron transport layers?ETLs?to get a desirable interlayer with high charge transport ability.And we adjusted the content of lead sources in precursor,as a result,the qualities of perovskite films were greatly improved.The details are as follows:?1?Fullerenes and its derivatives are the mostly used ETLs in the p-i-n type Pero-SCs.To systematically study the differences of charge transportation mechanisms of ETLs and the effect of processing methods of ETLs on the device performance,two vacuum-evaporated fullerenes(C₆₀,C₇₀)and solution-processed derivatives(PC₆₁BM,PC₇₁BM)were used as ETLs in Pero-SCs.As it was,compared with the evaporated fullerene layers deposited on perovskite films,the spin-coated PC₆₁BM and PC₇₁BM layers were more flatten and uniform,which can fill up the pinholes on the surface of perovskite films resulting in low charge recombination.The PCEs of devices based on the PC₆₁BM and PC₇₁BM as ETL were both above 14.0%.Besides,PC₇₁BM ETL showed better free charge extractation and transportation abilities than that of PC₆₁BM.?2?ZnO films are commenly prepared by sol-gel method?SG-ZnO?and hydrolysis-condensation method?HC-ZnO?.However,the reported device properties of Pero-SCs with those two ZnO films as ETLs were diverse.Moreover,the comprehensively study about the properties of SG-and HC-ZnO films,and the relations of device performance of Pero-SCs based on those two ZnO films are lacking.Therefore,we selected SG-and HC-ZnO films as the ETLs of the Pero-SCs and systematically studied their device preformances.After optimizing the thicknesses of the ZnO films,the best device based on HC-ZnO film exhibited a PCE of 12.9%,whereas,that was only 10.9%for the device based on SG-ZnO film.The impendence spectra,conductivity and fluorescence?PL?spectra accordantly proved that HC-ZnO film shown better charge transport abilities.Further,in order to protect the perovskite film from the hydroxyl group on the surface of HC-ZnO film,a thin C₆₀ layer was inserted between perovskite film and HC-ZnO film by vacuum evaporation,resulting in the morphology improvement of perovskite film.Therefore,the PCE of the best device was elevated to 14.1%.?3?The quality of perovskite film is a critical factor for the device performances of Pero-SCs,but it is difficult to prepare a uniform and compact perovskite layer by one step method.Herein,we proposed a new method by controlling the content of lead sources in precursor to improve the film quality of perovskite.The results shows that the coverage and rughness of perovskite films were greatly improved after a certain amount of Pb I₂ was added in perovskite precursor solution based on Pb?CH₃COO?₂ or PbCl₂.The PL spectra indicated that the defects could be effectively reduced after a certain amount of PbI₂ cooperated with Pb?CH₃COO?₂ or PbCl₂ to prepare perovskite films.Thus,the recombination of free charge in perovskite film could be suppressed,which was contributed to the effective transportation and collection of charge carriers.In the Pb?CH₃COO?₂-based Pero-SCs,the PCE of the best device was 11.0%that had increased by 18%compared with the blank reference device after 10wt%of PbI₂ was added into precursor solution.Similarly,as for PbCl₂-based Pero-SCs,the PCE of the best device was 16.2%with 40 wt%of PbI₂ added into precursor solution and that increased about 27%in comparison to the reference device.