Preparation Of NiO_x Hole Transport Layer For Perovskite Solar Cell Via Solution Combustion Synthesis

NiO_x is a wide bandgap?E_g>3.50 eV?p-type semiconductor with high optical transmittance,good electrical conductivity,great chemical stability,low cost,and energetically favorable energy level alignment with metal halide perovskite materials,which makes it very suitable as hole transport material for perovskite solar cells?PSCs?.However,most of the reported preparation methods for NiO_x hole transport layer?HTL?require high annealing temperature?>350°C?,which limits the application of NiO_x in perovskite solar cells.In this thesis,a new method,solution combustion synthesis?SCS?,was used to prepare NiO_x films as HTLs in PSCs.The influences of precursor concentration,annealing temperature,and molar ratio of fuel to oxidizer?F/O?on the NiO_x HTL and the performance of the PSCs were studied systematically,and the preparation conditions of the NiO_x HTL were optimized.The main contents of the paper are as follows:?1?Effects of the concentration of precursor solution:when the concentration of precursor solution gradually increased from 0.05 M to 1.0 M,the short-circuit current density J_sc,open circuit voltage V_oc,fill factor FF and power conversion efficiency?PCE?of the devices increased significantly first and then decreased slowly.This is mainly because when the concentration is 0.05 M,the surface coverage of the NiO_x film is low,and the shunt current of the device is large;as the concentration increases,the NiO_x film becomes thicker and the surface coverage is significantly improved,which can effectively reduce the shunt current of the device.But at the same time,the transmission resistance of the NiO_x layer is increased,and the light transmittance is reduced.The devices prepared at the optimal concentration of 0.1 M achieved the average PCE of 9.47%and the best PCE of 10.01%.?2?Effects of the annealing temperature of the precursor film:when the annealing temperature was 150°C which was below the critical temperature of the reaction,the prepared film was thick,and there was a lot of residual PbI₂ in perovskite film grown on the film.Accordingly,the PCEs of the devices were very low.At the annealing temperature of 200°C,the precursors reacted completely,and a dense and uniform NiO_x HTLs was formed.At the annealing temperature higher than 200°C,the films became thinner and with more holes as the temperature increased further,which led to increase of the carrier recombination probability and decrease of device performance.The devices prepared with the precursor concentration of0.1 M and the annealing temperature of 200°C achieved the best performance,with the average PCE of 10.77%,and the best PCE of 11.89%.?3?Effects of the molar ratio of fuel to oxidizer?F/O?:when F/O was less than 0.1,the temperature of the self-exothermic reaction was low,and the effective HTLs could not be formed and then the transport resistance was large.When the F/O was greater than 0.1,the temperature of the self-exothermic reaction was high,and the films were prepared with holes on them.At the F/O of 0.1,the optimal device performance was achieved,with the average PCE of 11.03%and the best PCE of 11.99%.?4?The work of this thesis demonstrates that the NiO_x HTLs can be prepared with SCS at a much lower temperature than with the conventional sol-gel method.It is worthy of further research on SCS preparation of NiO_x HTLs which has a good application prospect.