Synthesis And Photovoltaic Performance Of Small Molecule Acceptor With Six-membered Ring Bridge

Since the discovery of the non-fullerene fused-ring electron acceptor material ITIC,the efficiency of organic solar cells(OSCs)has been rapidly improved.Photoactive small-molecule acceptors(SMAs)are crucial for the efficient organic solar cells.There are three ways in developing acceptor-donor-acceptor(A-D-A)SMAs:donor core(D),electron withdrawing end group(A)and side chain engineering.In this paper,some SMAs based on pyrene or 2,6-bis(hexyloxy)naphthalene with six-membered-ring bridge were synthesized.The molecular structures of organic intermediates and SMAs were characterized.The thermal stability,photophysical properties and electrical properties of these SMAs were studied.Bulk heterojunction OSCs using these SMAs as acceptor materials were fabricated to investigate the photovoltaic performance.Main contributions of this work are as follows:1.Pyrene-based SMA FPIC6 with six-membered-ring bridge was synthesized.FPIC6exhibited excellent thermal stability and good intermolecular interaction in the solid state.Compared with the isomer FPIC5 with five-membered-ring bridges,FPIC6 exhibited more effective conjugation pathway,therefore the absorption peak of FPIC6 is 119 nm red-shifted,and the optical bandgap is reduced from 1.63 e V to 1.42 e V.OSCs based on PTB7-Th:FPIC6achieved the highest power conversion efficiency(PCE)of 11.5%,with open circuit voltage of 0.79 V,and short-circuit current of 21.50 m A cm^-2.Meanwhile,the PCE of PTB7-Th:FPIC5 device is just 8.45%,and the short-circuit current is 15.30 m A cm^-2.2.Six-membered-ring bridged SMAs PT-2H and PT-2F,using2,6-bis(hexyloxy)naphthalene as the core,were synthesized.Both PT-2H and PT-2F possessed good thermal stability and good solubility.The optical bandgaps of PT-2H and PT-2F are 1.66e V and 1.58 e V,respectively.From the solution to the film,PT-2F showed a more red-shifted absorption,indicating the better intermolecular?-?stacking.PT-2H and PT-2F exhibited the HOMO energy levels of-5.56 e V and-5.57 e V,and LUMO energy levels of-3.76 e V and-3.89 e V,respectively.The PCEs of OSCs based on PT-2H:PBDB-T or PT-2F:PBDB-T were5.11%and 11.15%,respectively.Six-membered-ring bridged SMAs always exhibited red-shifted absorption when compared with analogues with the common five-membered-ring bridge,and show great potential in OSCs.