| Organic solar cells(OSCs)have great potential to become the next generation of green energy due to their advantages of being light weight,semitransparent,flexibility,and roll to roll large-area processing.The morphology of active layer plays an essential role in the performance of OSCs devices.As a result,great efforts have been made to develop morphology optimization methodologies in order to fully realize the potential of photoactive materials.Recently,solid additives have shown great potential in fine-tuning the morphology,related to the aggregates,molecular packing,and domain size.This optimization facilitates exciton dissociation,charge transport,and collection,ultimately improving the power conversion efficiency(PCE)of the device.Unlike the traditional high boiling-point liquid additives,the volatile solid additives can be completely removed from the active layer by annealing without affecting the morphology of the device during the working process.This improves the stability of the device.Therefore,this paper designed a series of new efficient solid additives to efficiently control the active layer morphology of OSCs,and studied the working mechanism of solid additives.Additionally,to meet the needs of large-scale industrial manufacturing of OSCs in the future,this thesis also explored green halogen-free solid additives.The main research contents of this paper are as followings:1.Five biphenyl-type molecules were introduced as solid additives for OSCs.Due to their large molecular volume and good crystallinity,which leave a large vacancy in the active layer after volatilization.Additionally,the halogen atoms of molecules can enhance their interaction with acceptors.When the PM6:Y6 system was used,the five biphenyl-type solid additives showed excellent ability to improve the photovoltaic performance of the devices.Among them,the LB-I-based device achieved the highest PCE of 17.98%.This is because that LB-I can induce Y6 to form closer π-π packing and increase the D/A contact area in the blend film.Characterization of the photophysical properties of the device showed that LB-I can improve the exciton dissociation efficiency and carrier transport performance of the device,while inhibiting the charge recombination in the device.Furthermore,these biphenyl-type solid additives are highly volatile,improving the efficiency and maintain the stability of the device simultaneously.Finally,we found that LB-I can improve the PCE of multiple photovoltaic systems,suggesting a universality of LB-I,especially the optimized PM6: L8-BO device achieved an ultra-high PCE of 18.69%.Our work introduced a series of efficient solid additives for organic solar cells and provided new strategies for the design of new solid additives.2.We designed and synthesized a new halogen-free green solid additive,1,2,5-thiadiazole-3,4-dicarbonitrile(SA),which is capable of forming sulfur bond interaction with the N atom in the cyano group of Y6.This interaction efficiently controls the crystallization behavior of Y6 in films.Our results showed that the PM6: Y6 film,with the help of SA,formed a better twodimensional carrier transport network and a more balanced D/A phase separation morphology.This not only improved the exciton generation and dissociation ability of the device,but also inhibited the charge recombination behavior.As a results,the optimized device achieved a high efficiency of17.30%,while that of the control device is only 15.13%.Our findings offers insight into the mechanism of the interaction between the green halogen-free solid additive SA and the acceptors,and provide a new approach for large-scale green industrial manufacturing of OSCs in the future. |
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