Amino-Functionalized Graphene Quantum Dots as Cathode Interlayer for Efficient Organic Solar Cells: Quantum Dot Size on Interfacial Modification Ability and Photovoltaic Performance

In this work, a series of amino-functionalized graphene quantum dots (AF-GQDs) with different quantum dot sizes are prepared successfully and employed as the cathode interfacial layers (CILs) for fabrication of efficient organic solar cells (OSCs). The effect of quantum dot size on the interfacial modification ability and photovoltaic performance is investigated in detail. By varying the particle size of AF-GQDs, the work function of the cathode and the conductivity of CIL can be finely tuned. M-GQD with the medium size achieves the best balance of interfacial modification and conductivity, giving rise to the best power conversion efficiencies both in fullerene and nonfullerene OSCs (poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b ']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl-C-71-butylic acid methyl ester (PC71BM) blend: 10.14%; poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b ']dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c ']dithiophene-4,8-dione)] (PBDB-T):3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene) (ITIC) blend: 11.87%; and poly[(4,8-bis(5-(tripropylsilyl)thiophen-2-yl)benzo[1,2-b:4,5-b ']dithiophene)-co-(5,6-difluoro-2-(2-hexyldecyl)-4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3]triazole)] (J71):ITIC blend: 12.81%). This work not only provides a new type of high-performance CIL materials but also demonstrates a simple way for fine-tuning the interfacial modification ability and the conductivity via just controlling the quantum dot size of AF-GQDs.