Studies On The Thermostability Of Perovskite Solar Cells

Lead halide semiconductor materials with a perovskite crystal structure can be deposited as defect-tolerant polycrystalline thin films using solution-based techniques.These remarkable films exhibit excellent properties for harvesting solar light and transporting charge carriers,which can serve as light-harvesting active layers in solar cells,enabling efficient conversion of solar energy into electrical energy.In pursuit of high power conversion efficiency and stability of perovskite solar cell using wide bandgap oxide films as electron transport layers,it is necessary to unravel the influence of the hole transport layer and its interface with the perovskite layer.By combining theoretical simulations and experimental measurements,this thesis will explore the impact of hole transport layers on the thermal degradation of perovskites,also examine the effects of chemical structure of hole transport layer component upon energy levels,hole extraction,hole transport,glass transition,species diffusion,photovoltaic characteristics,and thermostability.Furthermore,this thesis also investigates the effects of interfical modification on defect density,excited state characteristics,photovoltaic characteristics,and thermostability.The main points are as follows:1)This thesis has synthesized an organic salt,4-（tert-butyl）pyridinium bis（trifluromethanesulfonyl）imide（TBPHTFSI）,which exhibits good thermal stability and high solubility in non-polar solvents,and could effectively enhance the air oxidation doping of the organic semiconductors,.The research discovered that organic coatings with different glass transition temperatures significantly influence the thermally induced degradation of perovskite.By incorporating a small amount of poly（9-vinylcarbazole）（PVK）with TBPHTFSI and spiro-OMe TAD,a semiconducting composite with a high glass transition temperature of 102℃ was achieved,while maintaining nearly unaffected transport properties.As a result,perovskite solar cells with exceptional thermostability at 85℃ for 500 hours were successfully fabricated.The analysis of device degradation confirmed the crucial role of the organic hole transport layer in maintaining the thermal stability of perovskite solar cells.It is worth noting that replacing PVK with polyacenaphthylene,despite its high glass transition temperature,presents a significant challenge.This suggests that the stability of the device may also depend on the intricate interaction between the components of the hole transport layer and the perovskite layer.2)Through photovoltaic measurements,surface analysis,and theoretical simulations,trifluorothymine,which possesses both Lewis acid and base sites as well as hydrophobic moiety,can serve as a molecular passivation agent for triple cation based halide perovskites.The lead and iodine promoted self-organization of amphiphilic trifluorothymine molecules can not only remove some electron and hole traps on the surface of perovskite and attenuate interfacial charge recombination,but also markedly reduce the thermal decomposition of hybrid perovskites and control the cracks of organic hole transport layers.Perovskite solar cells with a trifluorothymine interlayer maintain about 90%of initial efficiency after 1000 h aging at 85℃.This thesis has revealed that the construction of a powerful molecular interlayer is beneficial to the enhancement of both efficiency and stability of perovskite solar cells.3)This thesis has investigated a molecular semiconductor,H2,with a simple structure,suitable energy levels,high conductivity,and a high glass transition temperature.Considering that the low electrical conductivity of neat H2 based films,TBPHTFSI is blended with H2 to increase the hole density and hole mobility.The resulting H2-based composite exhibits a hole density of2.4×10¹⁸ cm^-3,a hole mobility of 9.3×10^-4 cm² V^-1 s^-1,an electrical conductivity exceeding 100μS cm^-1,and notably,a glass transition temperature exceeding 110℃,along with low gas permeation coefficients.These combined features enable the fabrication of perovskite solar cells with 85℃,1000h thermostability.4)The efficiency of perovskite solar cells utilizing spiro-OMe TAD as the hole transport material has been persistently enhanced,approaching nearly to 26%.However,these high-efficiency cells are unable to withstand the harsh heat at 85 ^oC.This thesis has investigated a spirobifluorene based hole transport material,SBF-FC,with highly asymmetric fluorenylcarbazolamine as the electron-donor.Compared to spiro-OMe TAD,SBF-FC exhibits a comparable HOMO energy level,but the glass transition temperature is almost twice as high.The composite produced by blending SBF-FC and TBPHTFSI demonstrates a room temperature conductivity of 49μS cm^-1 while retaining a high glass transition temperature of 176 ^oC.Importantly,the SBF-FC based hole transport layer,deposited onto the surface of FAPb I₃ thin film,exhibits more uniform morphology,leading to a significant improvement in device efficiency.This is mainly attributed to enhancements in series resistance,shunt resistance,and reverse saturation current.Moreover,the SBF-FC hole transport layer exhibits reduced diffusion of intrinsic and extrinsic species and durable morphology at 85 ^oC,effectively suppresses the corrosion and decomposition of the perovskite layer.The use of SBF-FC has enabled the fabrication of perovskite solar cells with an average efficiency of 24.5%,maximum power point stability and long-term thermostability at 85℃.