Dihlock Copolymer PF-b-PDMAHMA As Cathode Interfacial Layer For The Highly Performance Polymer Solar Cell

Polymer solar cells(PSCs)have received more and more attention in recent years,due to the advantages of low cost,solution processing and the capabilities to be fabricated into flexible and semitransparent devices.The power conversion efficiency(PCE)of PSCs has exceeded 15%,which could meet the requirements of commercial production.However,the PCE and stability of the devices are still the urgent problems that need to be solved in their commercialization process.To solve these problems,we focus on interfacial modification to fabricate highly efficient PSCs with higher PCE and better stability.In this paper,diblock copolymers poly[2,7-(9,9-dihexylfluorene)]-block-poly[2-(dimethylamino)ethyl methacrylate](PF-b-PDMAEMA)was applied as cathode interfacial layer(CIL)in PSCs,which facilitated the charge transfer between active layer and metal cathode,and improved the stability of the devices.This thesis mainly includes the following two aspects.(1)Diblock copolymer PF15-b-PDMAEMA75 was introduced as CIL to prepare a high-performance PSC.The device with PF15-b-PDMAEMA75 as CIL obtained a champion PCE of 8.80%,with an enhanced open-circuit voltage(Voc)and fill factor(FF).Compared with the device without CIL,the improvement of the device performance is mainly attributed to the two aspects:(a)Diblock copolymer effectively reduced the work function(WF)of the Al cathode,and improved the build-in voltage of the device,which could facilitate the charge extraction and transportation.(b)Diblock copolymer PF15-b-PDMAEMA75 effectively isolates the chemical reaction between the active layer and the electrode,improving the stability of the device.(2)We investigated the effect of the amino groups number in PDMAEMA block on the performance of the PSCs.Three copolymers with varying length of PDMAEMA block were synthesized and denoted as PF15-b-PDMAEMA60,PF15-b-PDMAEMA150 and PF15-b-PDMAEMA975.Meanwhile,homopolymer PDMAEMA was also synthesized to investigate the devices performance influenced by PF block.The results show that all four polymers working as CIL could effectively improve the PCE of the PSCs based on PTB7-Th:PC71BM active layer system.The surface dipole moment increased from PF15-b-PDMAEMA60,PF15-b-PDMAEMA150,PF15-b-PDMAEMA975 to PDMAEMA when applying the four CILs on top of the active blend film,which can effectively reduce the WF of cathode and facilitate electron extraction and collection.However,an obviously change of active layer morphology after coated with PDMAEMA break down the balance of charge transfer.Consequently,the device based on PF15-b-PDMAEMA975 as CIL achieved a champion PCE of 9.51%.The above studies show that PDMAEMA and diblock copolymers are excellent cathode interfacial materials.Especially when PDMAEMA combined with polyfluorene,the high PCE and enhanced stability of the devices exhibited less influence of the length of the PDMAEMA CIL,which effectively avoided the impact of diblock copolymers batches of the CIL on the performance of PSCs.