Preparation And Optimization For High Stability Carbon-based Perovskite Solar Cells

Recently,the perovskte solar cell?PSCs?based on organometal halide perovskte films have attracted a great deal of attention due to their preeminent photovoltaic performance and simple preparation process.Since the initial report on applying perovskite materials in solar cells back in 2009,impressive progress in enhancing the photovoltaic performance has been made and their power conversion efficiency?PCE?has skyrocketed to over 23%from 3.8%.Nevertheless,the decomposability of MAPbX₃?MAPbX₃?perovskite crystal and high-cost of noble metal electrodes?Au or Ag?or holes transport materials?HTM?limit the practical application of PSCs.Therefore,it is urgent to find an abundantly and inexpensive available material as counter electrode to replace the noble metal for developing a new-type PSCs without HTM.Carbon,as one of the most common and cheap materials,possess good conductivity,flexibility and similar work function with Au?carbon?-5.0 eV?,Au?-5.1eV??and exhibit great potential for applying in counter electrode.In this paper,we use carbon materials instead of noble metal metals as counter electrodes?CE?to prepare PSCs without hole transport layer?HTL?.In order to improve the photovoltaic performance and stability of devices,there aspects,included perovskite materials preparation,mesoporous layer modification,and device structure improvement,have been studied.The main contents of this paper are as follows:?1?The equimolar PbI₂ and MAI were added into DMSO-DMF mixture solvent with different volume ratios to prepare perovskite precursor solution.The effects of solvents with different volume ratios on the morphology and structure of perovskite films were studied.The characterization results indicatd that the perovskite film based on 2:8 exhibited excellent crystallinity and surface coverage compared with other films along with strongest light absorption intensity.The structure of prepared devices is FTO/TiO₂ compact layre/TiO₂-ZrO₂ mesoporous layer/MAPbI₃/C and their photovoltaic properties were tested.The results shew that the device based on 2:8exhibited the best photovoltaic performance:V_oc=0.86 V,J_sc=17.09 mA/cm²,FF=0.44,?=6.48%.?2?The perovskite precursor solution was prepared by adding NH₄Cl into DMSO-DMF mixed solvent with volume ratio of 2:8.The addition of NH₄Cl could promote the further growth of perovskite films,leading to improving the coverage the decreasing the charge recombination.As a result,the device achieved higher open-circuit voltage(V_oc=0.92 V)and short-circuit current(J_sc=17.09 mA/cm²),thereby improving the PCE??=7.84%?.?3?The PbTiO₃-decorated TiO₂-ZrO₂ mesoporous scaffold layers were prepared via a modified pickling process.The introduction of moderate concentration of PbTiO₃ is seen to promote the perovskite film growing and crystallizing,leading to reducing charge recombination loss and defect density.However,excessive PbI₂ residue resulted form decomposition of perovksit crystal was found when mesoporous layer was treated by excessive concentration of Pb²⁺solution.Perovskite films based on x=0.05 M exhibited larger crystal block size,better film quality and higher surface coverage,and shew the highest light absorption intensity in the visible region?550-750 nm?,indicating that the optimal treatment concentration is 0.05 M.The structure of the assembly device was FTO/TiO₂ compact layer/PbTiO₃-decorated mesoporous layer/MAPbI₃/C.The device based on x=0.05 M exhibited lower carrier transport resistance and higher carrier composite resistance,leading to obtaining the best optoelectronic performance:V_oc=1.00 V,J_sc=21.72 mA/cm²,FF=0.49,?=10.55%.And the devices exhibited excellent long-term stability as the PCE value remain 90.3%of its initial value after 1008 h stored at air with high humidity.?4?The structure of the device was optimized and the ZrO₂ insulating layer was abandoned.MgTiO₃-TiO₂ core-shell structure mesoporous layer was fabricated via a pickling process.The introduction of MgTiO₃ shell could retard charge recombination at MAPbI₃/TiO₂ interface,which would improve the V_oc and PCE of the device.At the same time,because MgTiO₃ belongs to perovskite crystal structure,MAPbI₃ crystals may nucleate and grow on the surface of MgTiO₃ by heterogeneous nucleation,thus forming perovskite films with better crystallinity and larger crystal size.Perovskite films based on x=0.10M exhibit the best crystallinity and surface coverage,and exhibit the highest light absorption intensity in the visible region?550-750 nm?.The structure of carbon-based PSCs was FTO/TiO₂ compact layer/MgTiO₃-coated TiO₂mesoporous layer/MAPbI₃/C and their photovoltaic properties were tested.With the increase of treating concentration,V_oc and J_sc of the devices first increase and then decrease.When x=0.10 M,the devices achieved the best photovoltaic performance:V_oc=0.95 V,J_sc=22.62 mA/cm²,FF=0.48,?=10.39%.