Design,Fabrication And Simulations Of Highly-Efficient Ternary Organic Solar Cells

Organic solar cells based on organic conjugated polymer or small molecule semiconductors,which exhibit advantages such as multifarious materials,low weight,and the potential to fabricate flexible,large area and semi-transparent devices have attracted much attention in the past several decades.However,it remains challenging to achieve commercialized so far.Researchers have been trying to enhance the efficiency and stability by designing new materials and optimizing the devices and it can be significant to study the working mechanism for organic solar cells.This dissertation is focused on the investigation for the mesophase morphology,interfacial arrangement and the photophysical process for ternary blend organic solar cells.Firstly,we designed and fabricated the all-small-molecule ternary solar cells based on organic photovoltaic molecules.By treating the active layers for the solar cells with thermal anneal and solvent vapor anneal,we found the mesophase transition from alloy-like model to cascade model and proved it through morphological characterization,photophysical analysis and theoretical simulations.The best power conversion efficiency for ternary solar cells with alloy-like model was 8.48%and was enhanced to 10.26%with the cascade model,which is among the best efficiencies for all-small-molecule ternary solar cells.This work is a systematic study for the mesophase transition of ternary blend organic solar cells and provides important reference value for fabricating highly-efficient devices.Secondly,the all-small-molecule ternary solar cells system was further investigated by using atomistic molecular dynamics simulations and electronic-structure calculations.We have obtained several binary and ternary blend mixed region samples and then analyzed them.The statistical analysis results for the mixed regions indicated that in the optimal ternary blend,the existence of the third component could reduce the probability of finding the PC₇₁BM molecule docking with the electron-donating moiety at the donor molecules.And the electronic-structure calculations implied the modulated donor–acceptor interfacial arrangement is favorable to suppress the intermolecular recombination without impacting the exciton dissociation process and hence beneficial to the power conversion efficiency for the ternary solar cells.Lastly,we have introduced the small molecule with large intersystem crossing and reverse intersystem crossing rates into polymer donor–nonfullerene acceptor blends and fabricated ternary solar cells.After the introduction of the small molecule,the performance for the solar cells was enhanced from 9.64%to 11.71%.By characterizing the morphological and photophysical properties,we have attributed the enhancement to two kind of functions of the small molecule.That is,the small molecules which are doped in the acceptor phase could create extra transport passways for electrons so as to improve the electron mobility significantly,and the introduction of the small molecule dose lengthen the excited state charge lifetimes in the ternary blend films which may come from the intersystem crossing and reverse intersystem crossing processes.