Research Of Absorption And Hole Transport Layer To Improve The Performance Of Perovskite Solar Cells

The perovskite material CH3NH3PbX3(MAPbX3)has the advantages of solution process,low cost and wide absorption band,high absorption coefficient,excellent carrier mobility(single crystal is about 66 cm2 V-1 S-1),low exciton binding energy(<10 meV),up to 1 μm electrons and hole migration length and tunable optical band gap,etc.Perovskite materials are widely used in solar cells,light-emitting devices and photodetectors.There are great development in PVSCs in just a few years with maximum power conversion efficiencies(PCE)evolving from 3.8%in 2009 to a certified 22.1%in 2016.A variety of configurations and manufacturing processes have been made to improve the device performances of the PVSCs,including how to improve the PCE,repeatability,stability,hysteresis effect,low cost hole/electron transport materials.Therefore two functional layer of PVSCs including the absorption layer and hole transport layer are focused on in this doctoral thesis.This dissertation is divided into the following four parts:(1)Highly reproducible and photocurrent hysteresis-less reverse planar PVSCs with a configuration of ITO/PEDOT:PSS/MAPbI3/PC61BM/Ca/Al were demonstrated by a modified solvent annealing method in a two-step solution deposition(modified method).PbI2 film was annealing at 40 0C using the residue solvent after spin-coating,which facilitated the CH3NH3PbI3 perovskite absorption layer with high photovoltaic properties.The resulting device present a PCE of 12.12%,which increased 43%compared with that of the control device fabricated as literatures(control method).(2)The coordination effect on perovskite crystallization are studied here.The polycrystalline perovskite film formed from the solution has a large surface area and grain boundaries,which are unstable and susceptible to moisture attack.Moreover,natural hydrophilicity of MAPbI3 leads to a high water-absorption in the air.Although one-step method can be operate simply,the repeatability of resulting morphology and performance is relatively poor.The PVSCs with the structure of ITO/TiO2/(CH3NH3)1-x(DLPA)xPbI3/P3HT/MoO3/Ag was first fabricated using bifunctional ammonium carboxylate by two-step solution method.The surface morphology of the perovskite layer is improved after the addition of DLPAI,in which the grain boundary is obviously reduced and the surface is more compact,uniform,and smooth,which is attributed to the hydrogen bond between-COOH and-NH3+ groups.By optimizing the production process,the power conversion efficiency increased from 10.21%to 15.11%with a higher stability.(3)The inorganic hole transport material has the advantages of high stability and hole mobility.WO3 precursor was synthesized by two mild method,W powder and H2O2,WCl6 and n-propanol were used as raw materials,respectively,which was confirmed in the reverse plane PVSCs with a configuration of ITO/WO3/MAPbI3/PC61BM/Ca/Al,compare the two methods,the PCE of device according to the HTL prepared by W powder and H2O2 up to 12.07%,higher than WCl6 and n-propanol as raw materials(9.80%),which is consistent with its larger grain size and smooth surface.(4)A new carbazole based polymer(HB-Cz)was designed and synthesized by a facile "A3+B2" one-pot Suzuki polycondensation reaction.Owing to the hyper-branched structure and carbazole unit,HB-Cz is a promising candidate of hole-transporting material(HTM),which was confirmed in the perovskite solar cells(PVSCs)with a configuration of ITO/TiO2/MAPbI3/HB-Cz/Ag.The films of P3HT and linear PCz were also used as hole-transporting layers(HTLs)in the reference devices.Time-resolved photoluminescence(TR-PL)spectra indicate that HB-Cz has fastest charge regeneration.Electrochemical impedance spectroscopy(EIS)revealed that HB-Cz reduced carrier recombination effectively,improving the open circuit voltage(Voc)and fill factor(FF)of the PVSCs.A PCE of 14.07%obtained from HB-Cz based device was much higher than those of the devices based on P3HT(9.05%)and PCz(6.60%),which is attributed to the superior hole transporting property and surface smoothing effect of HB-Cz HTL.