Perovskite Solar Cells Based On Titanium Dioxide Nanofibers/Nanorods

Perovskite-based solar cell?PSSC?evolve from dye-sensitized solar cell?DSSC?.The photoelectric conversion efficiency of PSSCs has been enhanced to about 20 % just after a few years of development since its emergence in 2009,and it was ranked as one of the annual world's top ten scientific progresses by Science in 2013.PSSC is attracting more and more attention due to its advantages of high conversion efficiency,simple preparation process,low cost,flexible large-area printing,and becomes a hotspot in the field of photovoltaic cells.At present,the methods of improving conversion efficiency and the stability of perovskite cells mainly include optimization of device structure,morphology control of perovskite crystalline thin films and modification of interface buffer layer.In this work,the influences of mesoporous layer,compact layer,and counter electrode on perovskite solar cells were investigated.First of all,mesoporous layer plays an extremely important role in perovskite solar cells,it is not only the electron transport layer,but also the support frame of perovskite sensitizer.The porosity of the mesoporous layer can lead to the growth of the perovskite grains,thus affect the crystallinity and morphology of perovskite.TiO₂ nanofibrous films were prepared on the treated FTO conductive glass by electrospinning,and the photoanodes of FTO conductive glass / TiO₂ compact layer / TiO₂ nanofiber layer were obtained by high temperature calcination.The samples were characterized by field emission scanning electron microscopy?FE-SEM?and X-ray diffraction?XRD?.The results show that the TiO₂ nanoparticles are composed of anatase after calcination at 500 °C.TiO₂ nanorods were prepared by sonication of electrospun TiO₂ nanofibers.The diameter and length of TiO₂ nanorods are about 100 nm and 2 ?m,respectively.The perovskite solar cells based on TiO₂ nanofibers have better photoelectric properties compared with those of perovskite solar cells based on TiO₂ nanorods.Second,one of the most important factors that affect the conversion efficiency of PSSCs is the recombination of photoelectrons and holes in HTM,resulting in a decrease in the current output efficiency.An effective method to suppress the recombination is to add a dense layer of TiO₂ between the FTO conductive glass and the TiO₂ nanocrystalline layer,which could suppressback-electron-transfer and improve the conversion efficiency of cells.TiO₂ compact layer was prepared by hydrothermal method and spin coating method respectively,and their effect on the photoelectric properties of PSSCs was investigated.To study the thickness influence of TiO₂ compact layer on solar cells,we prepared TiO₂ compact layers with different thickness by hydrothermal method.It was found that the optimum thickness of the compact layer is 300 nm.Finally,Au counter electrode of PSSCs must been prepared under high vacuum,which is not suitable for large-scale commercial production.Therefore,an excellent counter electrode material which can not only guarantee the performance of solar cells,but also improve the stability of cells is very important for PSSCs.In this paper,perovskite solar cells based on carbon counter electrode were prepared.Due to low conductivity and poor adhesion to the substrate of carbon counter electrode,the conversion efficiency of cells is lower than that of ones with Au counter electrode,much further research is necessary.In the whole,perovskite solar cells based on carbon counter electrode has great development potential.