The Research On The Fabrication And Properties For Inverted Planar Heterojunction Wide Bandgap Perovskite Solar Cells

Solar energy,as the energy source on the earth,possesses serveral advantages that differ from other energy,such as safety,environmental friendly and highly abundant,and etc.,has attracted much attentions recently.As a device for converting solar energy into electrical energy,the power conversion efficiency of solar cells is one of the key factors that determine their overall performance.The certificated efficiency of silicon cells is as high as 25.8%,which is close to the Shockley-Queisser efficiency limit,but their competitiveness such as price and scalability need to be further enhanced in order to play an important role as a sustainable energy source.To overcome the Shockley-Queisser efficiency limit,tandem solar cell design with stacked sub-cells composed of materials with different bandgaps can be adopted to reduce the overall thermalization loss in the photon-to-electrical conversion process.Such tandem solar cells can be fabricated by combining low cost wide-bandgap top cells with Si,copper indium gallium diselenide?CIGS?,polymer,and perovskite-based low-bandgap bottom cells.Therefore,the development of high performance wide bandgap solar cells is important.Planar heterojunction perovskite solar cells?PSCs?are emerging as a potential option due to their outstanding photovoltaic performance as well as low-cost solution processibility?tunable bandgap from 1.48².3 eV,positioning it as one of the most promising candidates for forming the tandem top cell.To match the bandgap of Si?1.1 eV?,a perovskite solar cell with bandgap of 1.7¹.8 eV is needed,which can potentially produce high device efficiency of above 30%.In this dissertation,we focus on the fabrication and optimization for high-efficiency and stability inverted planar heterojunction wide bandgap perovskite solar cells,which can be divided into following two parts:In chapter 3,we studied the effects of different I/Br ratio on the bandgap and absorbtion of MAPb(I_xBr_1-x)_3-yCl_y perovskite,then we choose a MAPb(I_0.7Br_0.3)_3-yCl_y film with a bandgap of 1.72 eV as the light absorption layer for wide-bandgap perovskite solar cell.To match the energy level for PEDOT:PSS layer and wide-bandgap perovskite layer,we modified the PEDOT:PSS with the polymer electrolyte PSS-Na,in order to deepen the HOMO level of PEDOT:PSS,a wide-bandgap PSCs with an efficiency exceeding 11%was successfully prepared.However,due to relatively complicated processing method and sensitivity of the film crystallization to humidity,the solar cells based on MAPb(I_0.7Br_0.3)_3-yCl_y films show poor reproducibility.Therefore,a series of optimizations have been made,such as the use of a perovskite component Cs_0.05(FA_0.8MA_0.2)_0.95Pb(I_0.6Br_0.4)₃ with better phase stability;modification of the processing of perovskite films with solvent dripping to obtain a uniform and smooth film;and change the material of the hole transport layer to obtain a more stable device.In addition,we also studied the effects of different NiO_x energy levels controlled by different annealing temperatures on the performance of wide bandgap PSCs.Finally,we successfully fabricated wide bandgap?1.75 eV?PSCs with a power conversion efficiency over14%with excellent reproducibility.Methylammonium iodide?MAI?is one of the key materials in the perovskite precursor solution.In Chapter 4,we intentionally increased the amount of MAI in the precursor solution and studied the effects of 1%?2%and 3%MAI-rich precursor solution on the performance of inverted heterojunction wide-bandgap PSCs.By studying the carrier kinetics in these solar cells,we found out that a small amount?1%,2%?of MAI rich in the perovskite precursor solution can reduce the recombination of carriers,increase the lifetime of carriers,shorten the charge-extraction time and improve the performance of PSCs.In addition,based on the PL and XRD studies of the perovskite films,we have proven that the excess amount of MAI can effectively inhibit the phase separation of wide bandgap perovskite films,which leads to increase in V_occ and reduce in energy loss of the device.Finally,we also studied the effect of excess MAI on the storage stability and illuminate stability of wide-bandgap PSCs,and verified the effect of phase separation of perovskite films on the illuminate stability of wide-bandgap PSCs.High performance PSCs with a PCE of 16.09%,FF of as high as 81.61%,and a bandgap of 1.75 eV were achieved.