Manjun Xiao

Enhancing the photovoltaic properties of terpolymers containing benzo[1,2-b:4,5-b′]dithiophene, phenanthro[4,5-abc]phenazine and benzo[c][1,2,5]thiadiazole by changing the substituents

In this study, three novel donor–acceptor (D–A)-type random conjugated terpolymers of PBDTT–PPzBT–H, PBDTT–PPzBT–F and PBDTT–PPzBT–O were synthesized by copolymerizing electron-rich 5,8-dialkylthienyl substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT) and two electron-deficient phenanthro[4,5-abc]phenazine (PPz) and benzo[c][1,2,5]thiadiazole (BT) units. By changing the substituents at the 5,6-positions of BT, the optoelectronic properties of the terpolymers could be rationally adjusted for application as donor materials in polymer solar cells (PSCs). As a result, these terpolymers exhibited different light absorption properties, HOMO energy levels and hole mobilities, which contributed to the optimization of short-circuit current (Jsc), open-circuit voltage (Voc) and fill factor (FF) properties, respectively. Interestingly, a maximum power conversion efficiency (PCE) of 6.3% was obtained with an Voc of 0.75 V, a Jsc of 13.0 mA cm−2 and a FF of 64.8% in the PBDTT–PPzBT–O based PSCs using [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor, while PBDTT–PPzBT–H and PBDTT–PPzBT–F based devices also demonstrated a PCE of more than 4.5%. To the best of our knowledge, these are the highest recorded maximum PCE, Jsc and FF values obtained to date compared with previously reported phenazine copolymeric derivatives in BHJ-PSCs. This study illustrates the potential of these random conjugated terpolymers as promising donor materials in the application of PSCs.

Tuning the central fused ring and terminal units to improve the photovoltaic performance of Ar(A–D)2 type small molecules in solution-processed organic solar cells

Low band-gap A–Ar–A and Ar(A–D)2 type small molecules (SMs) of DPP2Py, ThDPP2Py and TPADPP2Py were designed and synthesized, in which pyrene (Py) and diketopyrrolopyrrole (DPP) were respectively used as central aryl (Ar) and arm acceptor (A) units and 2-octylthiophene (Th) and triphenylamine (TPA) were employed as terminal donor (D) units. The effects of the central aryl and terminal units on optical, electrochemical, morphological and photovoltaic properties were primarily investigated. Compared to the reported analogues of DPP2Ar, in which Ar respectively represents 1,4-phenylene, 2,6-naphthalene and 2,6-anthracene, both DPP2Py and ThDPP2Py showed significantly improved photovoltaic performance in solution-processed organic solar cells. Furthermore, ThDPP2Py exhibited better photovoltaic performance than DPP2Py in these cells under optimized processing conditions. An improved power conversion efficiency (PCE) of 5.88% with a short current density (Jsc) of 15.35 mA cm−2 and a fill factor (FF) of 57.89% was obtained for the ThDPP2Py based OPV cells. Our research result demonstrates that properly extending the central aryl ring and appending terminal units in A–Ar–A type SMs can significantly improve the photovoltaic performance of Ar(A–D)2 type SMs.