Defect Passivation And Its Mechanism Of Perovskite Solar Cells

Perovskite solar cells?PSCs?have attracted extensive attention in industry and academia fields due to the high energy conversion efficiency,low cost of raw materials and simple device preparation methods.PSCs are mainly composed of five parts,which are conductive glass substrates?FTO or ITO?,electron transport layer,hole transport layer,perovskite photoabsorption layers?organic-inorganic hybrid perovskite material or pure inorganic perovskite material?and electrode?gold,silver or carbon material?.However,the grain boundary defects in the perovskite photoabsorption layers and the interface defects in the transport layer restrict the photoelectric conversion efficiency and stability of the PSCs.Therefore,it is very important to explore the mechanism of defects and to find an effective methods of passivation defects.Here,this paper combined theoretical and experimental methods to reduce the defects,thus improving the efficiency and stability of PSCs.The research results are as follows:?1?Efficient PSCs were prepared by regulating the diameter of One-Dimensional TiO₂nanorod array?NAs?.TiO₂is a popular material used as electron transport layer,which can effectively extract photogenerated electrons and block holes from perovskite.Nevertheless,TiO₂nanoparticle materials have a large number of grain boundary defects between the particles,thus greatly reducing the performance of electron transport layer.Hence,one-dimensional TiO₂NAs was prepared in this paper.TiO₂NAs has a direct one-dimensional electron transport channel,which can improve the extraction and transmission efficiency of electrons,thus improving the photoelectric performance of PSCs.Here,TiO_xseed-layers via annealing under different temperatures.When the annealing temperature increases from 100°C to 500°C,the average diameter of TiO₂NAs decrease from 74 to 31 nm.In addition,smooth TiO_xseed-layers improve the vertical orientation of the TiO₂NAs.The TiO₂NAs were further applied as photoanodes in carbon-based PSCs without hole conductor layers.The fine and vertical TiO₂NAs enhance performance of PSCs,which mainly results from the improved charge transfer and excellent transmission.The carbon-based PSCs TiO₂NAs with annealed the seed layer at 500°C achieved the best photovoltaic performance with power conversion efficiency?PCE?of 10.15%.On the contrary,the PCE of the device with the same structure based on common TiO₂nanoparticles was 7.18%.?2?TiO₂@CdS core-shell nanorods were used as electron transport layer to prepare efficient and stable PSCs.Despite the advantages of TiO₂NAs,there are a large number of oxygen vacancy defects on the surface of TiO₂materials under the irradiation of ultraviolet light for a long time.These defects will produce defective energy levels inside TiO₂,which can reduce the photoelectric performance and stability of PSCs.In consequence,it is very important to modify the surface of TiO₂to reduce the oxygen vacancy defect.In this work,enhanced efficiency and light stability of PSCs were achieved by the introduction of TiO₂@CdS core-shell nanorods films.The CdS shell was coated on TiO₂NAs by a simple chemical bath deposition method at room temperature.As a result,we got a champion PCE of 17.71%when the CdS is deposited for 10 min.Meanwhile,the light stability of PSCs was extremely improved by added the CdS,89%of initial PCE was maintained after 10 h continuous illumination.The reason of significantly enhanced efficiency and stability is the CdS shell could suppress recombination between the trapped electrons of TiO₂originating from the oxygen vacancies and perovskite,which is confirm by open-circuit voltage decay and electrochemical impedance spectroscopy.Specially,this is the first report that TiO₂@CdS core-shell nanorods as an electron transporter layer for PSCs,which is an excellent candidates as the electron transport layer in the fields of PSCs.?3?Mn²⁺was added to perovskite precursor solution to prepare high-quality perovskite films and excellent-property PSCs.In addition to the presence of defects at the interface,there are a large number of defects in the perovskite structure at the grain boundary,such as dislocation,impurity defects and vacancy defects due to the breaking of chemical bonds at the grain boundary.Finding an appropriate method to passivate defects is crucial to application of perovskite solar cells.The optimization results from first principle calculation reveal that Mn²⁺can easily insert into the interstices of octahedral[Pb I₆]^4-to restrain the generating of vacancy defects accompanying with perovskite crystallization.Meanwhile,it was found that Mn²⁺can improve microcrystalline thin films during the annealing process and reduce the recombination in experiments.When 1%Mn²⁺excessive doped in the MAPb I₃,the perovskite film has larger crystal sizes than that of pristine MAPb I₃film.Eventually,the efficiency of perovskite solar cells based on 1%Mn²⁺excessive doping is up to 19.09%,which is superior to 17.68%of the MAPb I₃-based devices.Herein,PSCs based on partial replacement of lead with manganese have been prepared.There is still an efficiency of 6.40%when the substituting content increased to 12.5 mol%.Consequently,perovskite solar cells based on Mn-incorporated have enormous potential application and provide a potential pathway for the non/less-lead hybrid perovskite materials.?4?A trace amount of Rh³⁺can effectively passivate grain boundary defects during perovskite film formation,which is prepared more efficient and stable PSCs.Besides manganese ions can passivate grain boundaries,we also looked for a large number of other elements.We found that trace Rh³⁺incorporation can also passivate grain boundaries,and achieved higher efficiency and longer stability.Herein,tiny amounts of trivalent rhodium ion incorporation can help the nucleation of perovskite grain and passivate the defects in the grain boundary,which can improve efficiency and stability of perovskite solar cells.Through first principle calculations,rhodium ion incorporated into the perovskite structure to induce ordered arrangement and tune bandgap.In experiment,Rh³⁺incorporation with perovskite can contribute to preparing larger crystalline and uniform film,reducing trap-state density and enlarging charge carrier lifetime.By comparing the PSCs based on MAPb I₃:x Rh?x=0,0.5 mol%,1 mol%,5 mol%?,the PSCs based on 1 mol%Rh³⁺incorporation achieved efficiency up to 20.71%without obvious hysteresis,from 19.09%of that pristine perovskite.In addition,the unencapsulated solar cells maintain 92%of its initial efficiency after500 h in dry air.This work highlights the advantages of Rh³⁺-doped in the characteristics of devices,which is promoted the future industrial application.