The Effect Of Surface Treatment Of TiO₂ Nanorod Arrays On Photovoltaic Performance Of Perovskite Solar Cells

One-dimensional TiO2 nanorod arrays have been widely used in new-type perovskite solar cell(PSC)because of its direct electronic transmission channel,high carrier mobility,good crystal matching with organic-inorganic hybrid perovskites(CH3NH3PbX3,where X is a halide of Cl,Br,I,etc.),suitable band gaps,relatively stable physical and chemical properties etc.In this dissertation,the rutile TiO2 nanorods arrays were prepared by traditional hydrothermal method and used as electron transporting materials and perovskite-loading scaffolds in PSC.Then,the TiO2 nanorods were further treated by some surface treatments and interface engineering treatments.Moreover,the influence of these surface modifications and interface engineering treatments on photovoltaic performance,suppression of the hysteresis,stability of the device,and significance for promoting industrial development is also deeply discussed.The more detailed research content is shown as follows:1.Firstly,the compact layer was obtained by putting FTO into TiC14 aqueous solution via chemical bathing deposition treatment.It was noteworthy that this compact layer could do help the synthesis of highly ordered TiO2 nanorods in hydrothermal growing process.As a result,the power conversion efficiency(PCE)of PSC can significantly increased from 7.48%to 11.10%.On the other hand,the influence of TiO2 nanorod arrays's thickness on photoelectric performance of PSC was also studied in detail.It was found that the best PCE of TiO2 nanorod arrays-based PSC could reach at 12.97%when the thickness is about 500 nm,due to the balance of electrons' transportation and diffusion through the TiO2/perovskite interface.What's more,the samples of TiO2 compact layer/TiO2 nanorod arrays structure were further modified by different concentrations of TiCl4 aqueous solution chemical bathing deposition treatment.Owing to the introduce of TiO2 nanoparticles on the surface of TiO2 nanorod arrays,not only the specific surface area of the nanorod arrays could be obviously increased,which do help enlarge the loading amount of perovskite,but also the physical contact between the perovskite grains and electron transporting material would be greatly optimized for reducing the gap of nanorod arrays and suppressing carrier recombination effectively.After treated with 0.1 M TiC14 solution,the PSC devices of TiO2 compact layer/TiO2 nanorod arrays/TiO2 nanoparticles/perovskite/Spiro-MeOTAD/Au would show the best excellent photoelectric performance with the short-circuit current density(Jsc)of 22.88 mA/cm2 and PCE of 15.11%respectively.2.The influence and application of TiO2 nanorod arrays modified by PCBM in PSC devices have been also conveyed in our research.It seems that the modification of PCBM can not only increase the Jsc because of PCBM's excellent electron conductivity,but also would significantly inhibit the hysteresis phenomenon of the device.After the optimize of PCBM treatment,compared to the PSC devices without PCBM treatment,the PCE of assembled devices with TiO2 nanorod arrays treated by PCBM at a concentration of 15 mg/ml were the best and PCE would increase from 13.82%to 15.36%at reverse-scanning model under AM 1.5 sunlight illumination.What's more,the PCBM modification would significantly reduce the difference between PCE at reverse-scanning mode and PCE at forward-scanning mode from 34.9%(without PCBM modification)to 11.7%(with PCBM modification).These improvements of optoelectronic performance and suppression of hysteresis are mainly attribute to a better interface contact between electron transporting materials and the perovskite crystal,effectively reducing interface defects and charge accumulation at the interface after the PCBM's introduction.Therefore,the fill factor of the assembled device of PCBM modification would be also significantly enhanced and the resistance of devices could reduced,the device performance would be improved.3.In order to improve the stability of PSC performance,an effective interface engineering treatment of TiO2 compact layer/TiO2 nanorod arrays/SiO2 protecting layer nano-structure was also studied.An ultra-thin film of SiO2 protecting layer could reduce the carrier recombination from the TiO2 conductive band to perovskite due to the higher conductive bang of SiO2,moreover,this protecting layer could avoid the PSC contact with O2 and H2O in air.As a result,when the TiO2 nanorod arrays were immersed in SiO2 sol for 2 h,the assembled PSC device with SiO2 interface engineering treatment show the most excellent performance with the open-circuit voltage(Voc)of 1.05 V,the Jsc of 21.75 mA/cm2,the fill factor of 73.72%,and the PCE of 16.82%respectively.What's more,96%of the initial test PCE had been still maintained after the devices were exposed in the atmospheric atmosphere for four weeks.