Research On Carbon-based Hole Conductor-free Perovskite Solar Cells Based On Electron-transport Layer

Organic-inorganic hybrid perovskite materials have excellent optical and electrical properties,including low excition separationenergy,long carrier lifetime,and high light absorption coefficient.In the last decade,The power conversion efficiency?PCE?of perovskite solar cells?PSCs?have been improved from 3.8% to over 23% ,which demonstrates a great potential for future commercialization.However,to achieve power conversion efficiency?PCE?around 20% in PSCs,organic hole transport materials?HTMs?,like spiro-OMeTAD,and noble metal electrodes,usually Au or Ag,are needed.The usage of hydroscopic organic HTMs cause stability issues,while noble metals increase the fabrication costs of regular structure PSCs.In order to improve long-term stability and reduce the fabrication cost,HTM-free PSCs are proposed and attracted prosperous progress.This kind of PSC,with a carbon counter electrode,has demonstrated low manufacturing cost,good stabilities against moisture and high working temperature.Here,we investigated the electron-transport layer?ETL?of the HTM-free PSCs with carbon electrode.By designing composite nanostructured electron-transport layer or incorporating functional nano-materials,the performance of the PSCs has been improved.The dedetails are summarized as follows:?1?We designed a unique composite nanostructured ETL using 200 nm ZnO nanoparticles to modify ZnO nanorode array.Facilitated by the 1D nanorods structure of underneath ZnO scaffold,photogenerated charges can be quickly transported out of perovskite film with reduced recombination.The ZnO nanoparticles modify the the surface of ZnO nanorode array,increasing the coverage of the perovskite layer on the underlying ETL;therefore,the performance of the PSCs increased.With optimized the thickness of ZnO nanorode,the PCE of 11.2% is achieved.?2?We demonstrate that the introduction of Au@SiO₂ NPs into mesoscopic HTM free PSCs will significantly improve the Jsc as well as overall PCE due to the enhanced light absorption,ionization of the excitons and enhanced charge separation.The Au@SiO₂ core-shell structure helped to enhance the light harvesting and facilitate carrier transfer or separation without deteriorate charge recombination by avoid the direct contact of Au NPs with perovskite or carbon layer.With an optimal concentration of 0.3 wt% Au@SiO₂ NPs,our PSCs show an average PCE of 13.85% ,which is 15% higher than the reference PSCs based on pure TiO₂ with the efficiency of 12.01% .?3?We made efficient ETL with NaYF₄:Yb,Er@SiO₂ modified TiO₂ NRs to enhance the performance of HTM-free PSCs through improved charge transport dynamics.TiO₂ NRs facilitate the charge transportation,SiO₂ insulating layer containing NaYF4:Yb,Er@SiO₂ inhibits the charge recombination by separation of roughTiO₂withcarbonlayer.Furthermore,core-shellhexagonal NaYF4:Yb,Er@SiO₂ upconvert NIR light into visible region,thus increase solar spectrum usage range to 980 nm.At last,a champion HTM-PSC with high PCE of14.52% is obtained.