Modification Of TiO₂ And NiO Carrier Transport Layers And Their Applications In Perovskite Solar Cells

In the last few years,perovskite materials have obtained more and more attention due to their long charge carrier diffusion length,high absorption coefficient,suitable band gap,low exciton binding energy.Up to date,the power conversion efficiency of perovskite solar cell has increased from 3.8%to 23.7%,which is approach to that of crystalline silicon based solar cells.Mesoporous TiO2 is one of the most commonly used as electron transport layer in perovskite solar cells,but meso-TiO2 often requires high annealing temperature for obtaining high quality films.Futhermore,Ti02 has low conductivity and contains much more defect in the film,modification of TiO2 is required for improving its performance.In addition,Spiro-OMeTAD is one the most commonly used as hole transport layer for planar n-i-p heterostructure perovskite solar cells.Hence,adding the Li-TFSI and t-BP improve hole transport mobility to Spiro-OMeTAD as a p-dopant.However,the introduction of p-dopants has a negative impact on the long-term stability of perovskite solar cells.On the other hand,the synthesis of Spiro-OMeTAD molecules is complicated and expensive,which is not suitable for large-scale industrial production.So it is necessary to find a cheaper p-type semiconductor with high hole molibity and good ambient stability.To solve these issues,herein,we optimize the titanium dioxide thin film and prepare inorganic oxide NiO to replace Spiro-OMeTAD as the hole transport layer of planar heterojunction device,which improves the stability of the device,some details as follows:1.Co-doped TiO2 film was prepared by low temperature chemical bath deposition method.By optimize the concentration of CoCl2 in the TiC14 precursor solution,we also constructed the PSCs with structure of FTO/Co:TiO2/Perovskite/Spiro-OMeTAD/Au.It is found that the doping of Co2+makes the energy level of TiO2 layer more aligned with the perovskite layer,promotes the effective injection of photogenerated electrons,improves the mobility of carriers,and reduces the recombination of charge accumulation.When the doping concentration of Co is 1.0 mol%,an outstanding enhancement of the performance is achieved,the PCE of device is 19.24%,which is higher than the pristine TiO2-based device(16.49%).2.The Cys-doped TiO2 film was prepared by low temperature chemical bath deposition method.By adjusting the concentration of cysteine,we obtained a dense TiO2 film,passivated the interface defectsbetween the TiO2 and the perovskite layer,and reduced the nonradiative recombination.We also conducted the PSCs structure of FTO/Cys:Ti02/Perovskite/Spiro-OMeTAD/Au device.It demonstrated that that when the concentration of Cys is 0.5 mol%,a high PCE of 19.73%is achieved with almost negeligible hysteresis.3.Uniformly dispersed NiO nanocrystals were prepared by solution method,NiO nanocrystals were dispersed in chlorobenzene at different concentrations,and robust solution was obtained.We verified that the prepared NiO has high purity without impurities and good dispersion.By further optimizing the concentration of NiO solution,the PSCs based on FTO/Ti02/Perovskite/NiO/Au structure with all inorganic metal oxide charge transport layers were fabricated.When the concentration of NiO is 5 mg/ml,the device has a high PCE of 13.61%.It shows that the NiO has a superior performance of hole transport and good ambient stability.In addition,the whole preparation procedure of the device is under the low temperature(<150 ℃),which lays a foundation for the preparation of flexible large-area devices in the future.