Low bandgap n-type organic semiconductor (n-OS) ITIC has attracted great attention for the application as an acceptor with medium bandgap p-type conjugated polymer as donor in nonfullerene polymer solar cells (PSCs) because of its attractive photovoltaic performance. Here we report a modification on the molecular structure of ITIC by side-chain isomerization with meta-alkylphenyl substitution, m-ITIC, to further improve its photovoltaic performance. In a comparison with its isomeric counterpart ITIC with para-alkyl-phenyl substitution, m-ITIC shows a higher film absorption coefficient, a larger crystalline coherence, and higher electron mobility. These inherent advantages of m-ITIC resulted in a higher power conversion efficiency (PCE) of 11.77% for the nonfullerene PSCs with m-ITIC as acceptor and a medium bandgap polymer J61 as donor, which is significantly improved over that (10.57%) of the corresponding devices with ITIC as acceptor. To the best of our knowledge, the PCE of 11.77% is one of the highest values reported in the literature to date for nonfullerene PSCs. More importantly, the m-ITIC-based device shows less thickness-dependent photovoltaic behavior than ITIC-based devices in the active-layer thickness range of 80-360 nm, which is beneficial for large area device fabrication. These results indicate that m-ITIC is a promising low bandgap n-OS for the application as an acceptor in PSCs, and the side-chain isomerization could be an easy and convenient way to further improve the photovoltaic performance of the donor and acceptor materials for high efficiency PSCs.
1.Chinese Acad Sci, Inst Chem, CAS Key Lab Organ Solids, Beijing Natl Lab Mol Sci, Beijing 100190, Peoples R China 2.Ulsan Natl Inst Sci & Technol, Low Dimens Carbon Mat Ctr, Sch Energy & Chem Engn, Dept Energy Engn, Ulsan 689798, South Korea 3.Univ Chinese Acad Sci, Beijing 100049, Peoples R China 4.Soochow Univ, Coll Chem Chem Engn & Mat Sci, Lab Adv Optoelect Mat, Suzhou 215123, Jiangsu, Peoples R China