Preparation Of TiO₂ Electron Transport Layer By Magnetron Sputtering And Its Performance Of Perovskite Solar Cells

Organic inorganic hybrid perovskite solar cells（PSCs）have attracted a lot of attention from researchers due to their excellent properties such as high light absorption,excellent carrier mobility and rapidly increasing photovoltaic conversion efficiency（PCE）.Since its inception in 2009,the conversion efficiency of 3.8%has rapidly increased to the highest certified efficiency of 25.5%for a single cell.In addition to high quality chalcogenide films,high performance and dense Electron Transport Layers（ETLs）are also essential for the preparation of high efficiency PSCs,which play a role in transporting electrons,blocking holes and reducing electron-hole complexation in PSCs.In this paper,highly dense SP-TiO₂（Magnetron Sputtering-TiO₂）electron transport layers were prepared on fluorine doped tin oxide（FTO）transparent conductive glass by RF magnetron sputtering and further fabricated into planar heterojunction chalcogenide solar cells（PSCs）to study the effects of sputtering time,sputtering pressure,sputtering power and annealing temperature on TiO2 thin films.The effects of sputtering time,sputtering pressure,sputtering power and annealing temperature on the microstructure,photovoltaic properties and cell performance of SP-TiO₂-based planar heterojunction chalcogenide solar cells are investigated,and the preparation of TiO₂ ETLs by spin-coating and RF magnetron sputtering are compared and discussed.The main studies in this paper are as follows.（1）Sputtering deposition of SP-TiO₂ thin films on FTO conductive glass substrates using RF magnetron sputtering technology.The effect of sputtering time on the structural morphology and optoelectronic properties of the TiO₂ films was investigated,and the effect of sputtering time on the device performance of SP-TiO₂ ETL-based PSCs was also investigated.The results showed that the thickness of SP-TiO₂ films increased with increasing sputtering time and the transmittance decreased accordingly,but the thickness of the titanium dioxide films obtained by 45 min sputtering met the condition of enhanced transmission light interference and their samples reached the highest transmittance of 82.29%.the square resistance of SP-TiO₂ increased with increasing sputtering time,but the uniformity of the film surface resistance was enhanced.It was found that the SP-TiO₂ electron transport layer obtained after 45 min of sputtering showed the best photoelectric performance with a photoelectric conversion efficiency of 12.70%（2）SP-TiO₂ ETLs were prepared by modulating the sputtering pressure（0.3,0.5,0.7,1,3,5,7,9 and 11 Pa）and further prepared into PSCs on this basis.The effects of sputtering pressure on the structural morphology and optoelectronic properties of SP-TiO₂ films were investigated,and the effects of sputtering pressure on the performance of SP-TiO₂ ETL-based PSCs were investigated too.The results show that the transmittance changes as the sputtering pressure increases,reaching a maximum transmittance of 78.27%at 5 Pa.The surface roughness of the SP-TiO₂ films is based on the FTO surface and decreases with increasing sputtering pressure,while the surface square resistance of the SP-TiO₂ films increases with increasing sputtering pressure.The cell device achieved the best PCE of 12.45%at a sputtering pressure of 1 Pa,Jsc of 17.76 m A/cm~2,Voc of 1.01 V and FF of 67.09%.（3）SP-TiO₂ ETLs were prepared using the parameters of 0.5 Pa,150 W,45 min,8 Sccm,varying the annealing temperatures（RT,300 and 500°C）and further prepared into PSCs on this basis.the effects of annealing temperature on the thickness,morphology and optical properties of TiO₂ films were investigated and the effects of annealing temperature on the performance of SP-TiO₂ ETL-based PSCs devices.The results show that the permeability of SP-TiO₂ films increases with the increase of annealing temperature,and the surface mean square resistance decreases with the increase of annealing temperature,while the forbidden band width does not change much.While Voc,FF and PCE of SP-TiO₂ ETL-based PSCs all increase with the increase of annealing temperature,Jsc shows a trend of first increase and then decrease.The best photoelectric conversion efficiency of 12.42%was achieved after annealing at 0.5 Pa,150 W,8 Sccm and 500°C for 30 min.500°C annealing is most suitable for the preparation of SP-TiO₂ ETL-based PSCs.（4）SP-TiO₂ and SO-TiO₂ with a thickness of about 70 nm were prepared by RF magnetron sputtering and solution spin-coating methods respectively.The differences in the intrinsic mechanisms and the effects of the two experimental methods were investigated by comparing the thin film photovoltaic performance and the subsequent cell device performance of the PSCs prepared by the two methods.The results show that SP-TiO₂ has a better coverage and bonding effect than SO-TiO₂ and FTO substrate,and there are fewer holes at the interface.The devices prepared by SP-TiO₂ have lower short-circuit current density and higher open-circuit voltage than those prepared by SO-TiO₂,while the filling factor and photoelectric conversion efficiency are higher for SO-TiO₂.Magnetron sputtering can prepare highly dense TiO₂ electron transport layers suitable for planar-type chalcogenide solar cells at high open-circuit voltages.