Research On Crystal Regulation Of Active Layer And Interface Modification Of Device In Perovskite Solar Cells

With the energy crisis approaching,thin-film solar cells are attracting more and more attention.Since 2009,due to its excellent photoelectric properties,the photoelectric conversion efficiency of the organic-inorganic hybrid perovskite solar cells has rapidly increased from 3.8%to 25.2%.The key factors for high efficiency perovskite solar cells are the preparation of high-quality perovskite films and the interface layer of high efficiency carrier transport.In addition,due to the breakthrough of new materials,polymer solar cells have made great progress in efficiency in recent years.Through tandem or integrated schemes,their photoelectric properties can be complementary with perovskite materials.In this paper,the active layer crystallization and interface modification of planar n-i-p structure perovskite solar cells?PSCs?were studied,and the preliminary exploration of polymer/perovskite integrated solar cells was also made.The main conclusions and results of this paper are as follows:?1?Zn O thin films were prepared by low-temperature spinning coating method,and were used as electron transfer layer?ETL?for n-i-p perovskite devices.The results showed that in the two-step process of device preparation,double spin-coating with methylammonium iodide?MAI?precursors could reduce the variation range of perovskite film thickness,improve the quality of perovskite crystallization,as well as lifting the energy conversion efficiency and thermal stability of the device.In addition,the light soaking phenomenon and interface charge accumulation under extra bias were studied.It was found that the interface charge was closely related to the strength or duration of bias,and hysteresis exorbitant devices can work only in metastable state with high interface charge.This discovery explains the relationship among the interface charge accumulation,the hysteresis and the steady-state output of devices,which points the way for more efficient and stable solar cells.?2?To control the crystallisation and the Pb I₂ residue of the perovskite films,a small fraction of dimethyl sulfoxide?DMSO?was added to the second-step precursor of the two-step preparation method.It was found that DMSO additive in this approach was able to tune the crystallisation of the perovskite layers,the grain size,and the quantity of Pb I₂residue.The approach improved the molecular penetration to the original Pb I₂ layer,which altered the density of nuclei for crystallisation and promoted the growth of the crystals to larger sizes.By adjusting the fraction of DMSO,the average grain size of the perovskite film under the optimal conditions reached 933 nm.The optimized perovskite film showed excellent crystallisation quality and appropriate amount of Pb I₂ residue.The power conversion efficiency?PCE?has reached 19.3%,which was 19%higher than the one of control device.?3?Polyethylenimine ethoxylated?PEIE?/Sn O₂ double-layer composite electron transport layer?DC-ETL?was designed and prepared by inserting a PEIE intermediate layer between indium tin oxide?ITO?and Sn O₂ layers.Through systematic research on surface morphology,energy level,photophore physics and photovoltaic characteristics,a high-efficiency perovskite solar cell is realized.According to the analysis of AC impedance spectrum,the recombination resistance inside the perovskite film is higher and the interfacial charge-transfer resistance is lower after the thickness of PEIE layer is optimized.The results show that:First,the PEIE interlayer can adjust the surface energy of the DC-ETL,thus changing the nucleation speed and grain size of perovskite crystals.Secondly,the PEIE interlayer can regulate the energy level of the DC-ETL to optimize the charge transmission and collection efficiency.All the photovoltaic parameters of the corresponding devices were improved,and the energy conversion efficiency of the typical devices reached 21.3%after being certified by The Chinese Academy of Metrology.?4?Ethylene diamine tetraacetic acid?EDTA?was used as modified materials to prepare DC-ETLs and PSCs.After optimization,20.2%certified PCE were obtained.By analyzing the surface morphology,optical physics and optical properties of the devices,it was found that the principle of device optimization is very similar to the DC-ETLs with PEIE.The results show that the scheme of the DC-ETLs with underdeath modification layer has universality,which greatly expands the selection range of the modified layer materials.?5?A series of n-i-p polymer solar cells were designed,prepared,and optimized.On this basis,the integrated perovskite/bulk-heterojunction organic solar cells?IPOSCs?were prepared to break through the Shockley-Queisser limit of perovskite solar cells.By adjusting the spin-coating speed,annealing temperature and time,the fraction of additives,and self-assembly condition,organic solar cells with P3HT?CAS:104934-50-1?:PCBM?CAS:160848-22-6?,PBDB-T?CAS:145929-80-4?:ITIC?CAS:1664293-06-4?,and PM6?CAS:1802013-83-7?:Y6?CAS:2304444-49-1?as active layer have reached the highest efficiency of 3.53%,9.72%and 12.32%,respectively.Meanwhile,through the C-V characteristics,doping density?N_A?are calculated,which reveals the reason why the device optimization process can improve performance of solar cells.And then,PBDB-T:ITIC and PM6:Y6 was used as organic active layer,and devices with structure of ITO/PEIE/Sn O₂/Perovskite/PM6:Y6?or PBDB-T:ITIC?/Mo O₃/Au were prepared and preliminarily optimized.The power conversion efficiency of devices using PM6:Y6 as polymer active layer is up to 14.65%.The device needs to be further optimized,which will be the future research direction.