Morphology Control And Stability Of Ternary Organic Solar Cells

Ecological environment pollution has been made and is mainly caused by the over-exploitation and utilization of fossil energy at present.In the increasingly severe ecological environment pollution and energy shortage,it is urgent to develop new renewable energy.Among many new energy sources,organic solar cells（OSCs）have become a hot research spot in the solar energy utilization due to their advantages of abundant solar energy resources,clean,pollution-free and convenient use.In recent20 years,OSCs has made great progress,in which the energy conversion efficiency（PCE）has exceeded 18%in the non-fullerene system.However,in order to realized their commercialization,it is crucial to reduce the cost and improve the photoelectric conversion efficiency and device stability.Nowadays,adding the third component into the binary system has been proved to be an effective method to improve the photoelectric conversion efficiency and the film morphology.But there are few studies on the third component to regulate the active layer morphology and improve the photoelectric conversion efficiency and device stability,especially the effect of the active layer morphology on the device stability.Based on the above problems,in this dissertation,the morphology regulation and device stability of ternary OSCs were studied.The main content and progress in this dissertation include the following aspects:1.The bis（dodecyl）thiophene isobenzopyrans-based small molecular donors of TTi C12,Ti C12 and Tb C12 were primarily added into PTB7-Th:PC₇₁BM system as new third component to prepare ternary fullerene OSCs with two donors and one acceptor in active layer.It was found that the central and terminal groups in these small molecule donors played a great influence on the photoactive layer morphology and photovoltaic performance of the ternary fullerene devices.Compared with the PTB7-Th:PC₇₁BM binary devices,the PTB7-Th:Ti C12:PC₇₁BM ternary devices exhibited a PCE of 10.42%,which is increased by 13.8%.Moreover,after the ternary fullerene devices were placed in nitrogen atmosphere for 2304 h,the PCE of the device remained 82.7%of the initial value.It indicates that the device stability was significantly improved.2.The ternary fullerene organic solar cells were prepared with two donors and one acceptor by adding one of small molecular donors of Ti C12,Ti C8 and Ti C6 as the third component in PTB7-Th:PC₇₁BM system.The small molecular donors here contain the arm of di（alkyl）thiophene isobenzopyrans,the centre of difluorobenzothiaodiazole and the terminal of indendione.It is found that alkyl structures in small molecule donors as the third component also played a great influence on the photoactive layer morphology and photovoltaic performance of the ternary fullerene devices.Compared with PTB7-Th:PC₇₁BM binary devices,the PTB7-Th:Ti C8:PC₇₁BM ternary devices exhibited an increasing PCE of 11.12%,which is increased by 21.40%.More importantly,after the ternary fullerene devices were placed in nitrogen atmosphere for 1680 h,the PCE of the device still maintained85.4%of the initial value.The results show that the ternary devices have better photovoltaic performance and higher device stability than the binary devices.3.The ternary fullerene organic solar cells were made with two donors and one acceptor by adding small molecular donor of Ti C12 as the third component in PC₇₁BM and different polymer donor system.The used polymer donors here are PBDB-T,PM6 and J71.The used Ti C12 contain the arm of bis（dodecyl）thiophene isobenzopyran.The results show that the introduction of small molecule donor of Ti C12 as the third component can improve the efficiencies of charge collection,charge transport,exciton dissociation and charge extraction in ternary fullerene cells.As a result,ternary fullerene cells exhibited significantly improved energy conversion efficiency and device stability.Therefore,small molecular donor Ti C12,as guest donor,has a wide application in improving the photovoltaic performance and device stability in ternary fullerene OSCs.4.The ternary non-fullerene organic solar cells were made with two donors and one non-fullerene acceptor by adding small molecular donor of Ti C12 as the third component in different non-fullerene binary systems of PBDB-T:ITIC,PM6:IT-4F and PM6:Y6,respectively.The effects of small molecule donor Ti C12 on the active layer morphology and photovoltaic performance of the ternary non-fullerene OSCs were studied.Among these resulting ternary non-fullerene cells,the PM6:Ti C12:Y6ternary cells show the best photovoltaic performance and device stability.Compared with the PM6:Y6 binary cell,the PM6:Ti C12:Y6 ternary cells exhibited a significantly boosted PCE of 17.25%,which is increased by 16.3%.Moreover,after the PM6:Ti C12:Y6 ternary cells were placed in nitrogen atmosphere for 96 h,the PCE of the device remained 83.0%of the initial value.The study on morphology of the blend films indicates that introduction of small molecular donor Ti C12 can promote the intermolecular ordered stacking and orientation,which are available to form an interpenetrating network structure,adjust the phase separation size,effectively optimize the active layer morphology,and further improve the device stability.5.The ternary organic solar cells were prepared with one donor and two acceptors by adding one of non-fullerene small molecular acceptors of C16-1 and C16-2 as the third component in the fullerene binary systems of PM6:PC₇₁BM.The C16-1 and C16-2 consist of the arm of dicetyl thiopheno-isophenopyrane and the end of difluoro-indodione.It is found that the central structure of the small molecule acceptors as the third component played a great influence on the active layer morphology and photovoltaic performance in the ternary cells.Compared with the PM6:PC₇₁BM binary cells,the PM6:C16-2:PC₇₁BM ternary cells exhibited a higher PCE of 9.46%,which in increased by 8.5%.More importantly,after the ternary cells were placed in nitrogen atmosphere for 840 h,the PCE of the device remained 86.2%of the initial value.The study on morphology of the blend films shows that both highly crystalline small molecular acceptors can promote crystallization of the amorphous PM6:PC₇₁BM while they were introduced into the PM6:PC₇₁BM system to a certain extent.Therefore,the PM6:C16-2:PC₇₁BM blend film tended to form a stable morphology and the stability of the device was improved.6.The ternary fullerene organic solar cells were prepared with two donors and one acceptor by introducing porphyrin donors as the third component into the PTB7-Th:PC₇₁BM system.The used porphyrin donors contain MPor1 and MPor2with different end groups,as well as CS4,CS5 and CS6 with different side chains.It is found that the molecular structures of small molecular porphyrin donors have a great influence on the photoactive layer morphology and photovoltaic performance of the ternary fullerene cells.Compared with PTB7-Th:PC₇₁BM binary cells,the PTB7-Th:CS6:PC₇₁BM ternary cells exhibited a high PCE of 9.66%,which is increased by 5.5%.Interestingly,after the ternary fullerene cells was placed in nitrogen atmosphere for 288 h,the PCE of the device still maintained 82.7%of the initial value.The results show that small molecule porphyrin as the third component can improve the photon collection in active layer and promote the exciton dissociation rate.Therefore,the molecular arrangement is compact and orderly,as well as the phase distribution is more balanced in the thin films.The photovoltaic performance and stability of the device are improved in this work.