Application Of Polymers With Functionalized Side Chain In Photovoltaic Devices

Polymer solar cells have attracted much attention because of their simple preparation method,low cost and large area continuous production.At present,the photoelectric conversion efficiency of organic solar energy has exceeded 16%.However,compared with the traditional industrialized silicon solar cells,the photoelectric conversion efficiency still needs to be further improved.The interface material is an important method to adjust the work function.The design and selection of molecular structure and aggregate structure are important factors affecting the photoelectric conversion efficiency of polymer solar cells.Based on the development of ionic liquids,the effects of material preparation,film-forming properties and microstructure of interfacial materials on efficiency and efficiency repeatability are studied in this paper.The main contents are as follows:（1）Using small molecular ionic liquid 1-vinyl-3-butylimidazolium bromide as cathode interface layer,6.92%conversion efficiency was obtained in the formal devices of organic solar cells based on PTB7-Th:PC₇₁BM as active layer,which was significantly higher than that of the devices without cathode interface layer（6.44%）.By comparing the external quantum efficiency（EQE）,electrochemical impedance（EIS）,work function（WF）and dark J-V,the reasons for the improvement of JSC and VOC are analyzed.It fully shows that ionic liquids can be an excellent interface material by establishing an interface dipole between the organic active layer and the metal electrode,adjusting the interfacial work function and reducing the charge transport barrier.（2）Polymer ionic liquids（PIL）were synthesized by polymerization of small molecular ionic liquids（MIL）.The molecular weight thermal stability of polymer ionic liquids was characterized.The decomposition temperature of polymer ionic liquids was 260^OC,which had good thermal stability.Using it as the cathode interface layer of organic solar cells,the conversion efficiency of 9.04%in the formal device system based on PTB7-Th:PC₇₁BM as the active layer was obtained,which was 2.1%higher than that of the small molecular ionic liquids as the interface layer.The differences of film forming properties between scanning electron microscopy and atomic force microscopy were compared.The external quantum efficiency（EQE）,electrochemical impedance（EIS）and dark J-V of small molecular ionic liquids and high molecular ionic liquids as interfacial layers were compared,and the reasons for the increase of short circuit current JSC and filling factor FF were analyzed.It is concluded that excellent film-forming performance is a necessary condition for effective establishment of interface dipole,improvement of interface work function and high efficiency and repeatability.（3）Polymer ionic liquids were used as cathode interface modification layer of perovskite solar cells.Compared with J-V curves of devices without interface modification layer,device efficiency increased from 17.25%to 18.25%.Among them,the device filling factor FF increased from 0.78 to 0.82.It shows that polymer ionic liquids containing halogen ions can not only form interfacial dipoles.At the same time,it can passivate the surface defect state of perovskite and reduce the electronic transmission resistance.It has research value that can be further explored.