Research On Provskite Solar Cells With An Electron Transportation Layer Doped With Nonfullerene Material

Fullerene has many excellent properties as a kind of traditional electron transport layer?ETL?material for planar perovskite solar cells.It has matching LUMO with perovskite.It can be fabricated as a thin film on the surface of perovskite by low-temperature solution method.It can weaken the ion migration of perovskite by electrostatic action.And it can passivate the defects of perovskite film by filling and covering.However,the photovoltaic properties of perovskite cells with an ETL made by fullerene material are limited by its drawbacks such as easy aggregation,difficult energy level adjustment,narrow absorption range and low absorption efficiency.Nonfullerene materials are widely used as electron acceptor materials for organic solar cells because of their high tunable energy levels,adjustable spectrum absorption which can expand to near infrared band and adaptable crystallinity.In addition,the introduction of the ternary structure with mixed nonfullerene-fullerene double acceptors and organic electron donor makes the photovoltaic performance of organic solar cells improved greatly.So,in this work,we introduced the nonfullerene material Y6 into the perovskite solar cell with traditional fullerene PC₆₁BM electron transport layer,observed the photovoltaic performance of devices,and analyzed the functionary mechanism of the material.Firstly,the hybrid electron transport layer perovskite solar cells by doping Y6 into the electron transport layer were prepared.The performance of the devices has been greatly improved.In which,J_SC increased from 22.3mA/cm² to 23.4 mA/cm²;FF increased from 57.0%to 61.5%.As a result,PCE of the device increased from 13.3%to 15.0%.Reasons for this improvement of performance are as followed:a charge transfer state with lower energy can promote the dissociation of exciton faster when photogenerated excitons dissociate at the interface between perovskite and Y6?This is due to the lower LUMO of Y6 compared with PC₆₁BM.In addition,the blending of Y6 and PC₆₁BM can form a two-phase separated and interpenetrated network structure of electron transport layer,which can improve the transmission rate of free electrons effectively.Secondly,the perovskite films were treated with the solution of Y6 dissolved in chlorobenzene as the antisolvent,and the solar cells were fabricated based on perovskite film with Y6 antisolvent treatment.The experimental results show that the J_SC of the device was increased from 23.4 mA/cm² to 23.9mA/cm²,and FF was increased from 61.5%to 64.8%.As a result,the PCE of the device was increased from 15.0%to 16.1%.Besides introducing more exciton dissociation channels on the surface of perovskite,the restrain of ion migration in perovskite film due to the coordination of PbI₃^-/I^-in perovskite and Y6 introduced by antisolvent is also the reason why the performance of device has an improvement.Yet,Y6 can also fill the two-dimensional expanded defects on the perovskite surface such as the grain boundary,so as to reduce the deep trap energy level in the perovskite energy band structure,restrain the non-radiative recombination of carriers,reduce the scattering probability of carriers by defects in the process of carrier migration and improve the carrier mobility.Above all,the photovoltaic performance of the devices can be improved by introducing Y6 fullerene into the perovskite solar cell.This method provides a new idea for prepare high performance the perovskite solar cell.