Design And Mechanism Research Of High Performance Ternary Organic Solar Cells

As one of the new photovoltaic technologies,organic solar cells?OSCs?have the advantages of environmental protection,light-weight,low-cost and easy preparation,and is a research focus of energies.Among the strategies to improve the photovoltaic performance of OSCs,the ternary strategy is one of the effective methods to improve the device performance because it takes into account the simple device structure of single heterojunction cells and the strong photon harvesting ability of tandem cells.However,the development of ternary strategy still faces the following problems:Firstly,the photoelectric conversion efficiency?PCE?of OSCs has not reached the standard for practical applications,further improving the PCE is the key to developing high performance ternary OSCs;Secondly,the interaction between components in ternary OSCs has a very important impact on device performance.Therefore,reasonably utilize the third component to modulate the phase separation and charge dynamics of the active layer still needs further research;Thirdly,the stability of OSCs in the atmosphere is another key issue after the breakthrough of device efficiency.The impact of introducing the third component on the device stability is definitely worth exploring.Finally,the ternary strategy needs to be developed in the application of OSCs,such as semitransparent devices.To solve above issues,we rationally modulate the intermolecular interactions between the third component and host materials to improve the electric properties and micro morphology of active layers,and then achieve a series of ternary OSCs with high efficiency and stability.The main research contents and innovations are as follows:?1?High performance ternary OSCs were prepared through the intermolecular hydrogen bond interaction between the third component and the host system materials.The hydrogen bond interaction can improve the electric property of fullerene and induce the crystallization and stacking characteristics of molecules in the active layer.Organic small molecule coumarin 7?C7?was introduced in PTB7-Th:PC₇₁BM system as the third component to construct the ternary OSC.The hydrogen bond formed between C7and PC₇₁BM caused charge enrichment on the sphere of fullerenes and promoted the?-?coupling between PC₇₁BM and the polymer donor,and then accelerated exciton dissociation and charge transfer.The existence of hydrogen bonds not only weakened the aggregation effect of PC₇₁BM in the active layer,enhanced the crystallinity of donor,but also assisted ternary blended film to form a bi-continuous nano-interpenetrating network structure to ensure efficient carrier transport.Compared with the control device,C7 based ternary OSC achieved a high PCE of 12.45%,which exhibited an improvement of 31.88%.Furthermore,another organic small molecule DIBC was introduced as the third component in this system to verify the applicability of the hydrogen bond strategy.DIBC based ternary OSCs not only achieved high PCEs but also possessed excellent light and heat stability in the atmospheric environment.?2?Considering the non-fullerene acceptor based on the A-D-A type main chain planar structure would form severe aggregation in the blended film,we creatively utilized the hydrogen bond interaction between the third component and the acceptor to improve the crystallization and distribution of the active layer materials and then enhanced the performance of ternary OSCs.An organic small molecule DIBC was introduced into a binary system based on this type acceptor?IEICO-4F?.DIBC could form intermolecular hydrogen bond with IEICO-4F,which enlarged the stacking distance and weakened the crystallinity of IEICO-4F.Concurrently,the introduction of DIBC constructed the nano-interpenetrating network structure and formed high-speed electron transport channels.Based on these improvements,the ternary OSC based on PTB7-Th:IEICO-4F:DIBC achieved a high efficiency of 13.53%and excellent storage stability.Similarly,the PCE of the ternary OSC based on PBDB-TF:Y6:DIBC is as high as 16.41%.?3?Introduced a small organic molecule with?-?stacking effect in OSCs to enhance the self-absorption process in the host system by the unique excimer emission,and achieved efficient and stable ternary OSCs.An organic small molecule PTN was designed,synthesized and used as the third component in the OSC.PTN could form an excimer via?-?stacking effect and showed remarkable spectral red-shift in the solid film.The red-shifted PL spectrum promoted the self-absorption process in the active layer and enhanced the photons harvest of the device.PTN tended to have a planar skeleton structure that had a strong interaction with fullerenes and suppressed the aggregation of fullerenes.Using the green solvent EBz,the ternary OSC based on PTB7-Th:PTN:PC₇₁BM not only achieved a high PCE of 11.44%,but also obtained good storage,thermal and light radiation stability in the atmosphere.?4?Innovatively introduced delayed fluorescent materials as the third component in OSCs,benefitted from the long-lifetime energy transfer mechanism between the third component and the host system molecules,high performance ternary OSCs have been realized by the improved excitons lifetime,diffusion distance and reduced the recombination energy loss.An organic small molecule APDC-TPDA with delayed fluorescence characteristic was designed and used as the third component to construct ternary OSC.In the blended films,the long-lifetime excitons generated on APDC-TPDA could transfer to the donor by energy transfer process,which enhanced the excitons'diffusion distance and dissociation efficiency on donors.At the same time,the existence of APDC-TPDA can not only inhibit the adverse reverse energy transfer,but also improve the micromorphology and charge dynamics of the active layer.Finally,a high PCE of 17%was achieved for the ternary OSC.It's worth noting that ternary OSC based on this strategy achieved excellent storage,light and thermal stability in the atmosphere.The introduction of delayed fluorescent materials fundamentally solves the problems of short exciton lifetime and limited exciton diffusion distance of OSCs,and provides a new design idea for developing high-performance ternary organic solar cells.?5?A new method for fabricating semitransparent OSCs?ST-OSCs?has been presented.The surfactant DDO was used as the third additive to improve the crystallization and phase separation process of active layer,endowed the device with a good tolerance on film thickness,and then realized efficient ST-OSCs.Utilized PTB7-Th:PC₇₁BM as the main research system,DDO doped ST-OSC achieved a high PCE of 8.41%with an average transmittance?AVT?of 30.8%.Different from the near-infrared non-fullerene acceptors based ST-OSCs,this strategy dominated ST-OSCs achieved high PCE while ensuring the absorption of the whole visible region.Profit from the improvement of film morphology and charge dynamic process,DDO doped devices also showed superior light and thermal stability.In addition,this surfactant has universal applicability to polymer/fullerene,small molecule/fullerene and polymer/non-fullerene system based OSCs.