The Design And Synthesis Of Novel Fused-Ring Electronic Acceptors For Organic Photovoltaics

In recent years,organic solar cells?OSCs?have attracted lots of attention due to its low cost,light weight and flexibility,etc.Up to date,the most efficient OSCs are composed of a donor?D?,a polymeric material in usual and an acceptor?A?which is based on non-fullerene?NFAs?.Bulk heterojunction?BHJ?device architecture possess the blended donor and acceptor materials to form nanoscale interpenetrating network which can enhance the device efficiency by maximizing the D/A interfacial area and decreasing the distance for exciton diffusion at the same time.The frontier energy levels and the absorption in the solar flux of NFAs,due to the synthetic flexibility,can be easily manipulated.The research and development of NFAs has always been a key aspect in OSCs field.Understanding the structure-property relationships can be extremely helpful in designing and synthesizing efficient acceptors.In this dissertation,a series of fused-ring acceptors have been developed.The effects of trans/cis-configuration,different?-conjugation length and electron-withdrawing group on the properties of the fused-ring electron acceptors?FREAs?have been investigated.As well,the effects of alkyl chains on the properties of perylene diimide?PDI?-based acceptor-acceptor?A-A?type polymer acceptors with a twisted backbone have been explored.The main results are as follows:?1?We synthesized two different configuration fused-ring electron acceptors?trans/cis-ITIC?based on different configuration core?indacenodithieno[3,2-b]thiophene,IDTT?,end-capped with 2-?3-oxo-2,3-dihydroinden-1-ylidene?malononitrile?INCN?.The change of configuration could effectively adjust the coplanarity of molecular structure and show a certain twist.Compared to trans-ITIC,cis-ITIC had a lower HOMO energy level,a slight higher LUMO energy level and had a broader bandgap.Compared to the PTB7-Th:trans-ITIC device,the PTB7-Th:cis-ITIC device exhibited a higher open-circuit voltage but a low power conversion efficiency?PCE?.?2?Introducing the cis-configuration into PDI-based fused-ring acceptors,six fused-ring acceptors with different configurations or?-conjugation lengths or with fluorine substitution were synthesized.Compared to trans-configuration,cis-configuration had a wider energy gap,a lower HOMO and a slight higher LUMO;The increase of the?-conjugated system facilitated the delocalization of electrons over the molecular backbone and narrowed the bandgap;The introduction of fluorine atoms had no significant effect on the absorption of different configuration molecules,however,it would increase the exciton coefficient,while reducing the energy level and narrowing the bandgap,which was beneficial to the improvement of the short-circuit current of the device.?3?PPDIBT-Th was obtained by introducing the twisted FPDI-Th which two PDIs are fused with a thiophene into A-A type polymer FREAs.Then,the alkyl chains was introduced into PPDIBT-Th to obtain a twisted A-A type polymer fused-ring acceptor PPDIBT-Th-C6.Comparing these two polymer acceptors,it was found that the polymer acceptor with a twisted structure exhibited good non-planarity in both solution and film conditions.The introduction of alkyl chains was able to increase the HOMO energy level.The device based on this molecule had a larger short-circuit current density(12.15 mA cm^-2),showing a better PCE?4.95%?.