Side-chain Optimization Of Indacenodithiophene-based Non-fullerene Acceptors For Efficient Polymer Solar Cells

With the widespread attention of non-fullerene small molecule acceptors（NF-SMAs）,organic solar cells（OSCs）have been developed by leaps and bounds,and the photoelectric conversion efficiency of OSCs based on fused ring small molecule acceptors currently developed has exceeded 18%.The construction of high-efficiency non-fullerene acceptors is often through alkyl side chain engineering and end group engineering to optimize the small molecule acceptors to achieve higher short-circuit current density(J_sc)and power conversion efficiency（PCE）.In this paper,a class of non-fullerene small molecule acceptor materials based on indacenodithiophene（IDT）units are designed.It mainly discusses the photophysical properties,electrochemical properties,thermal stability,crystallinity,and the preparation of bulk heterogeneity of NF-SMAs by alkyl side chain engineering.The specific research is as follows:1.Based on the small molecule acceptor IDIC-4F,a simple and easy-to-obtain small molecule acceptor C4Ph-IDT-DFIC was designed,synthesized and used in polymer solar cells.This chapter mainly focuses on exploring the impact of alkyl side chain engineering on photovoltaic performance.It is found that C4Ph-IDT-DFIC has a lower band gap than IDIC-4F,and the absorption spectrum is red-shifted by 45 nm and has stronger crystallinity.In addition,PM6:C4Ph-IDT-DFIC devices exhibit higher and more balanced electron mobility compared to PM6:IDIC-4F devices.The PM6:IDIC-4F-based device shows a PCE of 9.26%with an open-circuit voltage(V_oc)of 0.84 V,J_scof 15.18 m A cm^-2and fill factor（FF）of 72.37%.Excitingly,the PM6:C4Ph-IDT-DFIC-based device shows a PCE of 10.47%with V_ocof 0.801 V,J_scof 17.78 m A cm^-2and FF of 73.49%.This work provides a feasible molecular design strategy to build high-efficiency NF-SMAs.2.According to the second chapter,the A-D-A small molecule acceptor has a narrow absorption range,intermolecular interactions and molecular aggregation.However,the optimization strategy of its side chain engineering is very successful.Therefore,in combination with our previous work,we designed a new type of unit based on IDT as D unit and 2-（5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene）malononitrile（2FIC）as A unit.The alkyl side chain is similar to the"balloon"A-D-D-A type narrow band gap NF-SMA C4Ph-IDT2-DFIC,and applied in polymer solar cells.Due to the enhanced intramolecular charge transfer（ICT）effect from IDT unit to DFIC unit,the absorption of C4Ph-IDT2-DFIC is significantly red-shifted compared to IDT2-DFIC,which is more conducive to the absorption of the spectrum.It is also found that the intermolecular aggregation of PBDB-T and C4Ph-IDT2-DFIC becomes too strong due to the alkyl side chain of C4Ph-IDT2-DFIC.It is not conducive to form a good phase separation of devices,not conducive to the adjustment of the morphology of the active layer,and not conducive to obtaining a device with a high fill factor and a more balanced mobility.The PBDB-T:C4Ph-IDT2-DFIC-based device shows a PCE of 9.23%with an V_ocof 0.86V,J_scof 16.39 m A cm^-2and FF of 65.87%.The PBDB-T:IDT2-DFIC-based device shows a PCE of 10.06%with V_ocof 0.91 V,J_scof 16.06 m A cm^-2and FF of 69.22%.