Alkoxy substituted benzodithiophene-alt-fluorobenzotriazole copolymer as donor in non-fullerene polymer solar cells

Abstract

A new benzodithiophene (BDT)- alt -fluorobenzotriazole (FBTA) D-A copolymer J40 was designed and synthesized by introducing 2-octyldodecyloxy side chains on its BDT units, for expanding the family of the BDT- alt -FBTA-based copolymers and investigating the side chain effect on the photovoltaic performance of the polymer in non-fullerene polymer solar cells (PSCs). J40 exhibits complementary absorption spectra and matched electronic energy levels with the n -type organic semiconductor ( n -OS) (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) acceptor, and was used as polymer donor in the non-fullerene PSCs with ITIC as acceptor. The power conversion efficiency (PCE) of the PSCs based on J40 :ITIC (1:1, w / w ) with thermal annealing at 120 °C for 10 min reached 6.48% with a higher open-circuit voltage ( V oc) of 0.89 V. The high V oc of the PSCs is benefitted from the lower-lying highest occupied molecular orbital (HOMO) energy level of J40 . Although the photovoltaic performance of the polymer J40 with alkoxy side chain is lower than that of J60 and J61 with alkylthio-thienyl conjugated side chains, the PCE of 6.48% for the J40 -based device is still a relatively higher photovoltaic efficiency in the non-fullerene PSCs reported so far. The results indicate that the family of the BDT- alt -FBTA-based D-A copolymers are high performance polymer donor materials for non-fullerene PSCs and the side chain engineering plays an important role in the design of high performance polymer donors in the non-fullerene PSCs.