Synthesis And Modification Of Planar Perovskite Solar Cells

Global energy demand has significantly grown over the past few decades,and converting solar energy intoelectricalenergy is one of the most promising ways to meet this demand.Therefore,researchers fabricated various solar cells.Among all solar cells,perovskite solar cells?PSCs?developed rapidly in recent years.The power conversion efficiency of PSCs have surpassed 24%,which is comparable to conventional silicon-based solar cells.The excellent photovoltaic performance of PSCs makes it as a shining star of the next generation thin film solar cells.Planar perovskite solar cells?P-PSCs?exhibit highly efficient photoelectrical conversion capacity and have aroused increasingly attention due to their low fabricating costs,flexibility for device optimization and multijunction construction.The configuration of a typical planar perovskite solar cell is glass/transparent conductive oxide/electron-transport layer/perovskite light absorption layer/hole-transport layer/metal electrode.In recent years,intense efforts have been devoted to developing planar heterojunction PSCs and provided solar cells with power conversion efficiency exceeding 21%.In this paper,a planar perovskite solar cell based on transparent conductive glass FTO?SnO2:F?was fabricated,with titanium dioxide?TiO2?film as the electron-transport layer and perovskite material CH3NH3PbI3?MAPbI3?as the light absorbing layer.The photovoltaic performance of P-PSCs were boosted by improving the interface between TiO2 and MAPbI3.Firstly,the TiO2 films were prepared by spin-coating and used as the electron-transport layer of solar cells.Then,TiO2 nanocubic was adopted as a modifier by depositing on the spin-coated TiO2.As a result,a dual layer TiO2 film formed on the FTO.The TiO2 nanocubic provide a better platform for the growth of high quality perovskite absorber,and improved the interface between both.Next,sodium chloride?NaCl?was spin-coated on the TiO2.The introduced NaCl can adjust the band gap of MAPbI3,and the energy band of TiO2 and MAPbI3 matched better,which can effectively improve the electron-transport efficiency.At the same time,the photovoltaic performance of solar cells were improved.The main contents are as follows:?1?In perovskite solar cells,the quality of electron-transport layer is closely related to the performance of solar cells.The TiO2 films were deposited on clean FTO by spin-coating an acidic solution of tetrabutyl titanate?TBT?in ethanol,which was used as the electron-transport layer of perovskite soalr cells.The concentration of spin-coating solution were changed by controlling the content of TBT,as a result,different TiO2 films were prepared.The TiO2 films get thicker gradually with the increasing TBT content.The prepared planar perovskite solar cells achieved the best photovoltaic performance when the TBT is 0.07 mL,yielding a photovoltaic conversion efficiency of 10.24%,the corresponding short-circuit photocurrent density was 17.51 mA cm^-2,and the open-circuit voltage was 0.93 V,with a fill factor of 0.63.Then,perovskite films were prepared on the electron transport layer by one-step spin-coating and two-step spin-coating,and the properties of different perovskite films and corresponding devices were investigated.It has been found that one-step spin-coating method is more suitable for preparing the planar perovskite solar cells based on spin-coated TiO2 herein.?2?TiO2 nanocubic was adopted as an interfacial modifier between spin-coated TiO2 electron transport layer and MAPbI3 layer.We deposited TiO2 nanocubic on spin-coated TiO2 films by chemical bath deposition method.A TiO2 bilayer was fabricated on the FTO substrate after depositing TiO2 nanocubic on FTO/spin-coated TiO2 substrate,and the thickness of top TiO2 layer increased with the concentration of ammonium fluorotitanate??NH4?2TiF6?during the chemical bath deposition process.Scanning electron microscopy images and X-ray diffraction patterns indicated that the perovskite films deposited on the TiO2 bilayer possessed higher quality than on spin-coated TiO2.This can be ascribed to the top TiO2 nanocubic film which provided a better platform for the growth of perovskite films.The results of steady-statefluorescencespectroscopy,time-resolvedphotoluminescence spectroscopy and electrochemical impedance spectroscopy indicated that TiO2nanocubic can effectively suppressed the charge recombination at the interface between TiO2 and MAPbI3.The planar perovskite solar cell exhibited the best photoelectric performance when the?NH4?2TiF6 was 1 mM,and the open-circuit voltage increased from 0.93 V to 1.02 V compared with the device without TiO2nanocubic modifier.We obtained a photovoltaic conversion efficiency of 13.40%,which was 1.3 times of the device without TiO2 nanocubic modifier.?3?The band gap of MAPbI3 layer can be adjusted by spin-coating NaCl solution on TiO2.As a result,the energy band of both matched better,and the photovoltaic performance and stability of devices improved.The X-ray photoelectron spectroscopy test results show that NaCl coated on TiO2 uniformly.In addition,the band gap of MAPbI3 layer changed with the concentration of spin-coated NaCl solution.The band gap of MAPbI3 get wide,indicating that NaCl can adjust the band gap of MAPbI3.Due to the introduced NaCl,the grain size of perovskite films get larger and the lattice parameters changed.By optimizing the concentration of spin-coated NaCl solution,we found that TiO2 and MAPbI3possessed more suitable energy band position when the concentration of NaCl is 0.2mM/mL.And the photovoltaic performance of device achieved best when the concentration was 0.2 mM/mL.The device yielded a short-circuit current density of20.50 mA cm^-2,an open-circuit voltage of 1.06 V,a fill factor of 0.70,and the corresponding photovoltaic conversion efficiency was 15.58%,which was 15%higher than that of the un-coated NaCl device.At the same time,the hysteresis effect of device was suppressed,indicating that NaCl enhanced the photovoltaic performance of devices.In an environment of darkness,at room temperature,and humidity below 15%,the photovoltaic conversion efficiency of device maintained80%of the original efficiency after 1400 hours.