Research On Preparation And Mechanism Of High Performance Organic Solar Cells

Organic solar cells（OSCs）have received widespread attention due to their low cost,ease of manufacture,and low pollution.However,the device stability at this stage is still insufficient to achieve commercial applications.Multi-component strategy can effectively improve device efficiencies,but it is worth noting that the intermolecular interaction force between different components is very important to device performance.As a kind of intermolecular interaction force,hydrogen bonds have better directionality and selectivity thanπ-πstacking and van der Waals force,and can obtain regular molecular arrangement through self-assembly to optimize performance.Therefore,this thesis introduces intermolecular hydrogen bonds into the active layer to prepare high-efficiency OSCs.The main research contents are as follows:1.Apply hydrogen bond strategy to the active layer to build efficient ternary OSCs.According to the previous theory,the nitrogen-hydrogen group（N-H）on the dye molecule Coumarin 7（C7）can interact with the fluorine atom（F）on the IT-4F molecule to form a hydrogen bond to improve the device performance.Therefore,we use Fourier Transform Infrared Spectrometer（FT-IR）to prove that C7 can form hydrogen bonds with IT-4F,and then adding C7 into PTO2:IT-4F system to prepare ternary OSCs.C7 is complementary to the main system,and the hydrogen bond can be formed.The absorption spectrum of C7 is complementary to the main system.When 5 wt%C7 is added,the short-circuit current density(J_SC)and fill factor（FF）of the ternary device based on PTO2:IT-4F:C7 are improved.The J_SC grows from 20.15 m A cm^-2 to 22.02m A cm^-2,while FF increased from 68.50%to 69.96%,showing a power conversion efficiency（PCE）of 14.02%.Compared with the binary device（12.81%）,the PCE of the ternary device increases by 10%.The analysis found that hydrogen bonds can optimize the morphology of the active layer film and promote charge transfer,which indicates that the hydrogen bondg strategy is feasible.2.Based on the hydrogen bonding strategy,we separately introduced PC₇₁BM and Sudan Red 197（SR197）into PBDB-T-2F:Y6 system to prepare ternary devices.Then adding these two materials together to prepare quaternary devices and study the working mechanism of hydrogen bonds.As for ternary devices based on PBDB-T-2F:Y6:SR197,because the N-H group of the SR197 molecule could bind to the F atom of the acceptor Y6 to form a hydrogen bond,the morphology of the blended film is optimized and the bimolecular recombination is inhibited,thus obtaining a PCE of 16.83%.The ternary device based on PBDB-T-2F:Y6:PC₇₁BM reaches a PCE of 16.72%due to the isotropy and short-wave absorption of PC₇₁BM.On this basis,we introduced SR197and PC₇₁BM at the same time to prepare quaternary devices.SR197 can not only form hydrogen bonds with Y6,but also form hydrogen bonds with PC₇₁BM,thereby optimizing the morphology of the blended film and increasing the photon utilization rate,so the quaternary device achieves a PCE up to 17.48%.In addition,in order to prove the optimizing effect of performance hydrogen bonding on device performance,hydrogen bonds inhibitor methanol（CH₃OH）was added to inhibit the formation of hydrogen bonds.Experiment shows that after adding inhibitors,the performance of the devices containing hydrogen bonds are attenuated,while the devices without hydrogen bonds have no significant changes.In addition,the devices containing hydrogen bonds also show better light/thermal stability,indicating that hydrogen bonds can not only improve PCE,but also optimize device stabilities,which is beneficial to future commercial applications.We have analyzed the effect of hydrogen bonds on the improvement of device performance through experiments,and provided a feasible solution for the preparation of high-performance OSCs.