Highly Efficient Inverted Structure Perovskite Solar Cells

Organic-inorganic metal halide perovskites are an exciting class of semiconductor materials that possess many excelent properties desirable for various optoelectronic applications,such as tunable direct bandgap,high absorption coefficient,low exciton binding energy,balanced bipolar carrier transport and long carrier diffusion length.These properties make perovskite materials the most ideal light-absorbing materials for the new generation of solar cels.With the continuous optimization of thin-film fabrication process and device structure,the energy conversion efficiency of perovskite solar cels has increased rapidly from 3.8% in 2009 to 25.2% in 2019,which has surpassed the commercialized solar cels such as polysilicon,cadmium teluride and copper indium galium selenium,showing a very bright future.However,currently high-efficiency perovskite solar cels are based on the traditional structure?n-i-p?,because the use of ionic-dopant hole transport layer leads to the poor stability of n-i-p structure perovskite solar cells,coupled with the high price of the hole transport layer,which seriously hindered the commercialization of perovskite solar cells.Inverted structure?p-i-n?perovskite solar cell is becoming more and more attractive due to its characteristics of simple fabrication process,low cost,good stability and small hysteresis.However,the photoelectric conversion efficiency of p-i-n structure perovskite solar cells is far lower than that of devices based on n-i-p structure.The interface energy loss between perovskite and hole transport layer is the main reason for the low efficiency of p-i-n devices.The greater the interface energy loss is,the lower the open circuit voltage of devices will be.How to improve the open circuit voltage of p-i-n devices by reducing the interface energy loss between perovskite and hole transport layer is the focus of current research.In addition,because the current perovskite films are mainly prepared by solution-spinning and low-temperature treatment,various defects would be formed,which will act as the carrier recombination centers and affect the carrier lifetime,thus affecting the performance of the entire perovskite solar cels.This paper focuses on the structural design of perovskite solar cell with p-i-n structure and the research of perovskite composition engineering.We get the highly efficient and stable perovskite solar cels by optimizing the hole transport layer and passivating the perovskite film surface.It mainly includes the following specific works: 1.Dimethylamine molecule is used for efficient and stable inverted structure perovskite solar cellWe gained the MA_1-x DMA_xPbI₃ perovskite system by introducing the dimethylamine?DMA?to MAPbI₃ system,the introduction of the DMA reduces the defects density,increases the original perovskite structure rigidity,limits the ion migration in the lattice,thus improves the stability of perovskite thin films and devices under the condition of the air and light.We used NiO_x nanoparticles as the hole transporting layer?HTL?,MA_1-x DMA_xPbI₃ as the active layer,choline chloride as the passivation layer,C60 as the electron transporting layer?ETL?,BCP as the block layer and Ag as the electrode to fabricate the inverted structure perovskite solar cells with the structure of ITO/NiO_x/MA_1-x DMA_xPbI₃/Choline Chloride/C60/BCP/Ag.After the optimization of each layer,we gained the efficiency of 21.6% in the lab and the certified efficiency of 20.8%,which is the highest reported certified efficiency for NiO_x-based perovskite solar cels.And the devices showed excelent operational stability: encapsulated devices maintain over 80% of their efficiency following 800 h of operation at the maximum power point.2.The NiO_x film prepared at low temperature is used for efficient and stable narrow band gap perovskite solar cellsWe prepared the low band-gap tin-lead perovskite solar cell with the structure of: ITO/NiO_x/?FASnI₃?0.6?MAPbI₃?0.4/PCBM/BCP/Ag based on the low-temperature synthesized nickel oxide nanoparticles?L-NiO_x?as hole transport layer.By comparing the L-NiO_x films with the high temperature combustion synthesized NiO_x film?H-NiO_x?and the traditional PEDOT: PSS,we found that the band energy level of L-NiO_x is match well with that of the tin lead perovskite film.The Sn-Pb film based on the L-NiO_x showes larger grain size and lower trap density.And the Sn-Pb perovskite solar cels based on it show the efficiency of 18.8%,which is the highest efficiency of Sn-Pb perovskite solar cels based on the inorganic HTL.Also,the device based on L-NiO_x exhibit very good stability.After stored for 50 days in glovebox,the PCE shows negligible degradation.3.MA-free inverted structure wide-bandgap perovskite solar cellsWe studied the wide-bandgap perovskite materials without MA component,by adjusting the ratio of Cs,FA,DMA component,we got a wide-bandgap perovskite system with bandgap above 1.7 e V.Under the same bandgap condition,we found that vary the DMA content can reduce the Br content in the wide-bandgap system,which can inhibit the phase separation,thus increase the stability of wide-bandgap perovskite materials.Furthermore,the Cs FADMA-based wide-bandgap perovskite system exhibit excelent thermal stability for the reason of MA-free.We fabricated the inverted structure perovskite solar cells by using NiO_x as HTL and PCBM as ETL,the inverted structure Cs FADMA-based wide-bandgap perovskite solar cell shows the PCE of 19.7%,which is the highest efficiency of inverted structure wide-bandgap perovskite solar cells.Also,the device exhibit good thermal stability,which can retain above 80% of initial efficiency after stored at 85? for 168 hours.