Study Of High Performance Perovskite Solar Cell And Four-terminal Perovskite/Silicon Tandem Solar Cell

Perovskite photovoltaic materials have outstanding photoelectric properties such as high light absorption coefficient,high carrier mobility,low exciton binding energy and high defect tolerance.In the past decade,great progress has been made in the field of photovoltaic.The highest certification power conversion efficiency(PCE)of perovskite solar cells(PSCs)has reached 25.5%,which is close to the highest laboratory efficiency of single-junction silicon cells(26.7%).As the cost of single-junction silicon cells is high and approaching the efficiency limit(29.4%),further improvement of solar cell efficiency is faced with great technical difficulties and high-cost challenges.Based on this,the perovskite/silicon tandem cell technology is an important choice to effectively utilize the solar energy and break the theoretical efficiency limit of crystalline silicon cells.There are two key points in the preparation of perovskite/silicon tandem cells:one is the efficient and stable perovskite material system and the preparation of solar cells;The other is to prepare transparent electrodes with high electrical conductivity and high light transmittance.In order to obtain the perovskite solar cell and perovskite/silicon tandem cell with high efficiency,good stability and simple process,this paper focuses on the perovskite film crystallization and morphology regulation,interface modification and control of electron and hole transport layer in PSCs.Based on this,the theoretical calculation of transparent PSCs,the preparation of transparent electrode technology and the optical and electrical characteristics of the device were studied,and the preparation of four-terminal perovskite/silicon tandem cell was realized.The PCE of 28.3%was obtained,which was the highest performance of four-terminal perovskite/silicon tandem cell in the same period.The details are as follows:1.Regulation and modification of charge transport layer in perovskite solar cellsIn the ITO/SnO₂/perovskite/spiro-OMeTAD/Ag regular structure PSCs,by spin coating graphene quantum dots(GQDs)on SnO₂ ETL,the ETL/perovskite interface energy level matching was effectively improved and the carrier recombination problem was inhibited.The results showed that the open circuit voltage(V_OC)and short circuit current(J_SC)of PSCs based on SnO₂:GQD_S electron transport layer were increased to 1.11V and 24.4m A/cm²,respectively,and the final PCE was increased from 18.6%to 21.2%.In order to solve the instability problem of the spiro-OMeTAD,PMMA was mixed into the spiro-OMeTAD in a certain proportion.PSCs doped with 2 mg/m L PMMA obtained the optimal performance,and their PCE exceeded 21%.At the same time,the introduction of PMMA had greatly improved the storage stability of PSCs.After 80 days of storage at 25°C and 30%relative humidity,the device could still maintain 75%of the initial performance.The metal thermal oxidation of high-quality nickel oxide realized the perovskite/anode energy level matching and improved the interface hole-transporting and collection efficiency.Based on the method of metal thermal oxidation,inverse structure PSCs(FTO/NiO_x/perovskite/PCBM/Ag)acquired PCE of 18.13%,higher than that of conventional sol gel method NiO_x based PSCs(17.33%),and has high stability.After 90 days storage in air,the above PSCs can still retain94%of the initial efficiency.2.Physical properties regulation of perovskite light absorption layerFor the first time,the composition of perovskite films was regulated by the ternary mixed cations of MA⁺,FA⁺and Gua⁺.The introduction of guanidine salt reduces the initial nucleation point of perovskite and increases the crystallization time.In the crystallization process,the Ostwald ripening mechanism and the directional bonding growth mechanism dominate the growth of perovskite grains,resulting in the increase of grain size.The average grain size of perovskite films based on ternal-ion mixed cations is 0.9?m,and the maximum grain size is close to 1.3?m,which is much higher than that of MA⁺and FA⁺based perovskite films.The increased grain size reduced grain boundaries and internal defects,and the optimal PCE was 21.3%for PSCs based on Gua_0.1(FAMA)_0.9Pb_xCl_3-x component.The solid source diffusion process in crystalline silicon cell was applied to perovskite thin film cell.For the first time,cesium bromide(CsBr)was used as the solid diffusion source,and the asymmetric doping of perovskite layer was realized.The diffusion of CsBr into the perovskite bulk could form gradient distribution.Based on the space-charge-limited current(SCLC)test,via the CsBr passivation,perovskite defect density reduced from 2.81×10¹⁵cm³ to 2.39×10¹⁵ cm³.PCE of 22.1%was acquired(V_OCand J_SC are 1.15 V and 24.5m A/cm²).3.Study on metal/oxide composite transparent electrode and perovskite/silicon four-terminal tandem cellUltrathin transparent metal electrodes(Ag and Au)were prepared based on thermal evaporation process.The introduction of ultra-thin MoO₃ could improve the wettability of transparent metal electrodes,and TeO₂ could improve the light transmittance of transparent metal electrodes.Finally,efficient and stable bifacial transparent PSCs were prepared.Based on ITO/NiO_x/perovskite/PEAI/PCBM/Ag/TeO₂ structure,when illuminated from the ITO bottom electrode,the device showed a champion PCE of 20.96%,and when illuminated from the TeO₂/Ag top electrode,the same device achieved a PCE of 17.36%,with a bifaciality factor of 82.82%.To our knowledge,this is the first report of a bifacial PSC with a PCE of over 20%and bifaciality factor exceeding 80%.Meanwhile,large area(1cm²)bifacial transparent PSCs with efficiency of 12.42%and 10.55%on both sides are realized.Based on the regular structure of ITO/SnO₂/CsBr/perovskite/spiro-OMeTAD/MoO₃/Au/MoO₃,PCE of 21.4%from ITO side and 16.5%from Au side was achieved.Based on the optical transport matrix method(OTMM)and the drift diffusion equation,a perovskite/silicon four-terminal tandem solar cell model was constructed to simulate the photon absorption and carrier transport.The maximum theoretical PCE of the perovskite/silicon four-terminal tandem solar cell was 31.97%.Under the guidance of the theory,the efficiency of the silicon bottom cell maintained PCE of 6.9%after the semitransparent top PSCs shading.The semitransparent PSCs and silicon cells were further stacked,and the efficiency of 28.3%of the four-terminal perovskite/silicon tandem cells was achieved,which is the highest value of the four-terminal perovskite/silicon tandem cells.