Study On Properties Regulation Of CsPbBr₃ Film And Performance Of Printable Mesoscopic Perovskite Solar Cells

The photo-electric conversion efficiency(PCE)of hybrid organic-inorganic perovskite solar cells(PSCs)has increased from 3.8%in 2009 to 25.5%up to date,which is comparable with that of commercial silicon solar cells.The solution-based PSCs have become a research hotspot owing to the low cost.However,the stability of device structure and light-absorbing materials is the biggest obstacle to commercialization.The reason is that organic units of light-absorbing materials own low dissociation energy and inherent chemical instability;the irreversible diffusion of halide ions from the perovskite to the counter electrode and hygroscopicity of expensive hole-transport materials affects stability.All-inorganic perovskite CsPbI_3-xBr_x(0?x?3),that is,inorganic Cs⁺with higher dissociation energy is used to replace organic cations(such as MA⁺,FA⁺,etc.).By stabilizing the photosensitive phase and improving the crystal quality,efficient perovskite devices with higher thermal stability and ambient stability can be obtained;On the other hand,printable mesoscopic perovskite cells based on three-layer mesoporous TiO₂/ZrO₂/C film have great advantages in terms of cost,stability and large-area preparation.Herein,the above two aspects will be combined to carry out the following research:(1)We develop a space-confined method to fabricate stable lower-order symmetric pure monoclinic CsPbBr₃ phase at low temperature(<50?).Based on multiple-step deposition and high annealing temperature(>250?)to prepare the large-size perovskite,and the structural,optoelectronic properties and long-term stability change upon temperature-dependent phase-transition.It is found that the carbon-based printable mesoporous area can assist and stabilize low symmetric monoclinic phase compared with the traditional device.Therefore,the device exhibits a PCE of 7.52%with a low hysteresis index of 0.024.The record open circuit voltage(Voc)was 1.4602 V in the TiO₂-based optoelectronic device without interface modification.The theoretical calculation shows that the monoclinic CsPbBr₃ phase has a similar band gap and a smaller Pb-Br bond length compared with the cubic crystal structure,so it shows similar performance to the traditional cubic perovskite.Moreover,the device passed the 1000 hours' 85? thermal test and the 200 cycles thermal cycling test according to IEC-61625 stability tests.(2)The Eu³⁺was introduced into CsPbBr₃ perovskite to adjust the energy band position and improve the crystal quality by n-type doping.In view of the narrow absorption range and voltage loss caused by more defect states of monocline CsPbBr₃ perovskite.Eu³⁺was successfully introduced into CsPbBr₃ lattice,causing the upward shift of Fermi level,the downward shift of the conduction band minimum and the valence band maximum.By reducing E_fp,to a great extent,even on the basis of the downward shift of E_fn,the energy loss is effectively reduced,and thus improving the open-circuit voltage and fill factor;In addition,the crystal quality is effectively enhanced,the non-radiative recombination and defect states are reduced to some extent,and the band gap is narrowed,which significantly improves the light absorption and the short-circuit current density,thus improving the efficiency.The efficiency of the device improved from 7.5%to 8.06%with 3 mol%Eu³⁺doping,which contains an?7.46%improvements compared to those without Eu³⁺doping.Based on the device with effective area of 1 cm² and 60.075 cm²,the PCE of 5.41%and 1.14%is obtained.In addition,the experimental results show that two tandem devices can provide voltage to drive water electrolysis device,and the whole device has good stability.(3)We develop the Formamide,N-methyl Formamide(NMF)as a new type solvent engineering of PbBr₂,which effectively improve the quality of crystal through slowly crystallization by the way of auxiliary heat annealing.Based on the poor repeatability of CsPbBr₃ perovskite device using sequential deposition method,and low short circuit current density due to the bad quality of crystal.It shows that the defect states density and non-radiation combination center are effectively reduced,the light absorption capacity is significantly improved,and the short-circuit current density is significantly enhanced when compared with the DMF/DMSO based device.In addition,it shows that there are obvious differences of precursor particle size and solvent volatilization speed rules,and there is the best wettability of NMF on three layers films,the NMF-based device efficiency is increased from 7.53%to 8.32%,the repeatability is also improved significantly.In addition,the 1 cm² device achieve the efficiency of 5.62%,and the light stability of the photovoltaics increased significantly.(4)Based on the problems of poor perovskite compatibility,high toxicity of dispersants(chlorobenzene,toluene,etc.)of carbon electrode,and voltage loss caused by energy level difference between carbon electrode and perovskite in carbon-based hole transport layer-free photovoltaics(C-PSCs),we developed a low temperature carbon paste with high conductivity in previous work.Herein,a PCE of 11.7%is achieved by applying this carbon slurry to C-PSCs based on Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.7)3 perovskite.We further using PEDOT:PSS layer as interface modification layer,which effectively improved the ability of hole extraction and get the PCE of 14.5%.In addition,the PCE of 7.04%was obtained based on PEN/ITO/SnO₂/Perovskite/PEDOT:PSS/C.This universal carbon paste is expected to prepare low cost and large area perovskite.