| Organic photovoltaics(OPVs)have outstanding advantages such as simple device structure,light weight,available devices with flexibility and translucence,and have attracted extensive attention at home and abroad,so they have played an important role in the research field of photovoltaic devices currently.Especially in the past 20 years,the highest power conversion efficiency(PCE)of OPVs has been continuously updated,owing to the continuous emergence of high-efficiency materials in the active layer,the improvement of device's processing technology as well as the in-depth study of the working principle of OPVs.The working efficiency of OPVs based on a single active layer with bulk-heterojunction structure has surpassed the threshold of 16%.Considering the many branches of the research field of OPVs,all-polymer solar cells make use of polymer-based acceptor materials with strongly tunable chemical structure and high absorption efficiency for visible light.The open-circuit voltage and the short-circuit current density can be simultaneously increased by the means of reasonable molecular design of polymeric acceptors.At the same time,the active layers only made from polymers process high mechanical stability and thermal stability,which ensure sufficient working stability during the preparation and the use.Although all-polymer solar cells have shown great industrial potential,their improvement of PCE has been relatively small.The main reason is that the types of high-efficiency polymeric acceptor materials are relatively limited.To this end,we started from developing new high-efficiency polymeric acceptor materials in this paper.A variety of acceptor polymers based on naphthalene diimide(NDI)and perylene diimide(PDI)were designed and synthesized.We focused on further improving the PCE of all-polymer solar cells.In chapter 2,we designed and synthesized a series of NDI-type acceptor polymers based on repeating units: NDI-ethynylene-benzo[1,2-b:4,5-b']dithiophene(BDT),and systematically studied the effect of the change of the alkyl side chains in the NDI unit on the photovoltaic performance of the devices.The results show that the introduction of 2-octyldodecyl(OD)side chain can improve the orderly aggregation of the acceptor polymer in the active layer to the greatest extent,and optimize the morphology of the polymer blend film.A photovoltaic device with PNEOD as the acceptor polymer can achieve a relatively highest PCE of 3.44%.In chapter 3,we applied modification with functionalized side chains to the BDT donor unit in PNEOD,and obtained two sets of modified polymeric acceptor materials based on PNEOD.We studied the effect of species of the side chain to the performance of acceptor polymers,including light-absorption characteristics,level structure,charge-transfer capability and device efficiency.By comparative analysis,we found that the introduction of n-octyl side chain in PNEOD-C8 promotes the orderly close packing of the acceptor polymer in active layer and enhances the mobility of carriers,without changing the electronic energy level of the acceptor polymer.The PCE of the normal device using the PBDB-T:PNEOD-C8 active layer can be increased to 5.84%.In chapter 4,we selected PDI as the acceptor unit for the acceptor polymers and conjugated it with the BDT donor unit through ethynylene unit as ?-bridge,a series of PDItype polymeric acceptor materials were prepared in which BDT units had different functional side chains.The resulting polymers were applied to all-polymer solar cells.According to the test of mobility,the characterization of morphology about the blended films and so on,it was found that the target polymers have fine intermixture with the donor polymer due to their low molecular weight,but the limited percolation pathways promote bimolecular recombination and make the electron mobilities of the devices low,so the photovoltaic devices worked inefficiently.These results will play a guiding role in the design of PDI-type polymer acceptor materials. |
PDF Full Text Request