Application In Mesoporous Perovskite Solar Cells Of N-doped TiO₂ Nanocrystal Prepared By Pre-annealing

Lead halide perovskite has become an ideal light-absorbing material for solar cells because of its high light absorption coefficient,suitable band gap,bipolar charge transport,long electron hole diffusion length and carrier life,and high fault tolerance to defects.The photoelectric conversion efficiency(PCE)of perovskite solar cells has increased from 3.8%to 25.5%in the past few years since the perovskite material was first introduced as a light absorber in all-solid perovskite solar cells.This efficiency is even comparable to traditional commercial solar cells such as crystalline silicon,Cu In Ga Se and Cd Te.Typically,perovskite solar cells consist of an electron transport layer(ETL)and a hole transport layer(HTL)with a perovskite layer sandwiched between the two.In most perovskite solar cells,mesoporous TiO₂ is used as the electron transport layer material.However,although TiO₂ has the advantages of low cost,good transparency,high chemical stability,suitable band gap,etc.,its conductivity and carrier mobility are low due to many defect states,which reduce the efficiency and stability of perovskite solar cells.Therefore,TiO₂ must be modified by element doping and other strategies.By doping appropriate ions,such as Ru⁴⁺,Nb⁵⁺,CS⁺,Li⁺,the electron transport performance of mesoporous TiO₂ can be effectively improved.Fabrizio Giordano and Siraj Sidhik reported on lithium-and cobalt-doped TiO2.The surface treatment of mesoporous TiO₂ films by bis(trifluoromethane)lithium sulfimide salt(Li-TFSI)and cobalt salt(Co-TFSI or FK209)significantly improves the photoelectric conversion efficiency,and the hysteresis index is negligible.In addition,the mesoporous TiO₂ films used as electron transport layers require high temperature annealing to obtain anatase crystal structure,which impedes the application of mesoporous perovskite solar cells on flexible substrates.Therefore,the application of mesoporous TiO₂ in flexible perovskite solar cells should be considered when the defects of mesoporous TiO₂ are doped and passivated.In this paper,an N-doped TiO₂ nanocrystalline was studied and used as an electron transport layer in mesoporous perovskite solar cells:(1)First,N-doped TiO₂ nanocrystals were prepared by the combination of pre-annealing and ball milling.The N-doped TiO₂ mesoporous films are anatase phase and exhibit a continuous mesoporous skeleton composed of TiO₂ nanoparticles.The mesoporous perovskite solar cells assembled by N-doped TiO₂ nanocrystals have a high average power conversion efficiency of 16.65%.The photoluminescence spectra and impedance spectra showed that there was a good passivation defect in the N-doped TiO₂mesoporous film,which inhibited the carrier recombination.(2)Second,N doped TiO₂ for annealing,avoided ably to in the subsequent assembly device in the process of high temperature sintering of the mesoporous layer,can make the process under low temperature,and based on this,will be used for flexible substrate on the N doped TiO₂ nanocrystalline,preparation of the flexible perovskite solar cell components,got 14.52%of the photoelectric conversion efficiency.