Conjugated Polymer Based on Polycyclic Aromatics for Bulk Heterojunction Organic Solar Cells: A Case Study of Quadrathienonaphthalene Polymers with 2% Efficiency
✍ Scribed by Shengqiang Xiao; Andrew C. Stuart; Shubin Liu; Huaxing Zhou; Wei You
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 554 KB
- Volume
- 20
- Category
- Article
- ISSN
- 1616-301X
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✦ Synopsis
Abstract
Polycyclic aromatics offer great flexibility in tuning the energy levels and bandgaps of resulting conjugated polymers. These features have been exploited in the recent examples of benzo[2,1‐b:3,4‐b']dithiophene (BDT)‐based polymers for bulk heterojunction (BHJ) photovoltaics (ACS Appl. Mater. Interfaces 2009, 1, 1613). Taking one step further, a simple oxidative photocyclization is used here to convert the BDT with two pendent thiophene units into an enlarged planar polycyclic aromatic ring—**quadrathienon**aphthalene (QTN). The reduced steric hindrance and more planar structure promotes the intermolecular interaction of **QTN‐**based polymers, leading to increased hole mobility in related polymers. As‐synthesized homopolymer (HMPQTN) and donor–acceptor polymer (PQTN‐BT) maintain a low highest occupied molecular orbital (HOMO) energy level, ascribable to the polycyclic aromatic (QTN) moiety, which leads to a good open‐circuit voltage in BHJ devices of these polymers blended with PCBM ([6,6]‐phenyl‐C~61~‐butyric acid methyl ester; HMPQTN: 0.76 V, PQTN‐BT: 0.72 V). The donor–acceptor polymer (PQTN‐BT) has a smaller optical bandgap (1.6 eV) than that of HMPQTN (2.0 eV), which explains its current (5.69 mA cm^−2^) being slightly higher than that of HMPQTN (5.02 mA cm^−2^). Overall efficiencies over 2% are achieved for BHJ devices fabricated from either polymer with PCBM as the acceptor.