Preparation And Performance Optimization Of Perovskite Solar Cell Materials Based On TiO₂ Nanorod Arrays

Perovskite Solar Cells(PSCs)have become a research hotspot in recent years because of their excellent photoelectric properties and low preparation cost.With unique electron transport channels and oriented pore structures,the single crystal titanium dioxide nanorod arrays(TNRAs)have been used as PSCs electron transport layer materials.However,the power conversion efficiency and stability of TNRAs-based PSCs are still not ideal,and the toxic metal lead(Pb)in perovskite has hindered the commercialization of perovskite cells.To solve the above problems,this thesis aims to further improve the performance of TNRAs based PSCs by selecting and regulating PbI2 solvents,optimizing the energy level matching between "TNRAs/perovskite" interfaces,and passivating the perovskite grain boundary and surface defects.On this basis,metal element strontium(Sr)was selected to replace Pb to construct efficient eco-friendly PSCs.Different coordination ability solvents including DMSO,DMF,CH3COOH,CH3COCH3 and ACN were selected to investigate the nucleation and growth mechanism of PbI2 adduct and perovskite film by using a two-step spin-coating method.The solution DMSO+ACN was chosen as the optimal solvent due to its higher performance of the constructed device.Moreover,the effect of volume ratio of DMSO to ACN(VDMSO/ACN)on the perovskite film was systematically studied.The results indicated that more compact perovskite film with larger grain size could be formed with ACN amount increasing,which led to higher power conversion efficiency(PCE)of the solar cell.Dynamic light scattering(DLS)analysis of PbI2/DMSO+ACN solutions was used to elucidate the phenomenon.With the VDMSO/ACN decreasing from pure DMSO to 7:3,the radius of ACN-PbI2-DMSO clusters in solutions decreased from 694 nm to 365 nm,resulting the in formation of porous PbI2 adduct films,thus providing MAI solution more transport channels and adequate space for grain growth.Under the air relative humidity of 30%(RH=30%),the device PCE of 15.32%was achieved at the VDMSO/ACN of 7:3.By employing a two-step spin-coating method,the influence of PbI2 solvent such as PbI2/DMSO+ACN and PbI2/DMF+DMSO+HAc solutions,on the preparation and performance of TNRAs based PSCs was intensively investigated.The relationship between the micro-characteristics of perovskite film,especially the interfacial contact between perovskite film and TNRAs,and macro-properties of PSCs was elucidated.Results indicated that two compact perovskite films with similar large grain size were synthesized on TNRAs from the two different PbI2 solvents,which led to similar short circuit current densities(JSc).However,the PSCs from PbI2/DMF+DMSO+HAc solution showed a larger Voc of 1.06 V compared with that from PbI2/DMSO+ACN solution,and thus a higher PCE of 15.93%was achieved.The key reasons for the enhanced performance might be ascribed to the faster electron extraction and larger electron recombination resistance in the PSCs.In addition,the effect of NbCls concentration on the micro structure and photovoltaic properties of the formed perovskite films were investigated,and the enhancement mechanism was also elucidated.A champion efficiency of 16.50%was achieved when the concentration of NbCls solution was 0.005 M.Such an enhanced performance of PSCs might be mainly ascribed to two reasons:one was the improved perovskite film qualities including the enlarged average grain size,higher crystallinity and reduced defect density;the other was the formed energy barrier(Nb2O5)between perovskite layer and TNRAs interface that hindered the charge recombination.Using TNRAs as electron transport layer,MAPbI3 thin films were prepared in air by a two-step spin coating method.The crystal boundary defects and surface defects of perovskite were passivated by using octylammonium iodide(CH3(CH2)7NH3I,OAI)and choline chloride(HOCH2CH2N(CH3)3Cl,Ch),respectively.The effects of co-passivation on the properties of perovskite films,the efficiency and the humidity and heat stability of perovskite cells were systematically studied,and the passivation mechanism was also discussed.It was shown that the introduction of OAI enhanced the structural stability of perovskite films through the formation of intermolecular valence bonds.Ch passivated the Pb-I antisite substitution defect and I-vacancy defect on the MAPbI3 film surface.Due to the combined passivation,the average cell efficiency was increased from 16.77%to 17.21%,and the humidity and thermal stability of the device were further improved.Strontium chloride(SrCl2)was chosen to fabricate lead-less TNRAs based PSCs in air by a simple two-step spin-coating method.The influence of introduced strontium(Sr)on the perovskite films and cell properties was systematically investigated.With an increasing Sr substitution amount from 0 to 15 mol%,the formed perovskite films with a compact structure and large crystalline size essentially remained invariable,while the amount of residual PbI2 was reduced,which is beneficial for the cell performance.An optimal PCE of 16.08%was obtained for the 5 mol%Sr substituted PSCs because of the enhanced charge extraction from the perovskite films to the TNRAs and the suppressed charge recombination in the PSCs.Both the humidity and thermal stability of the Sr-substituted PSCs were improved.More importantly,the 15 mol%Sr-substituted PSCs still exhibited a PCE of 15.09%in air,maintaining 99%of the cell efficiency of the pristine(0 mol%Sr)PSC(15.27%),suggesting that the structure of TNRAs was suitable for the synthesis of high-performance Sr-substituted lead-less PSCs.