Abstract
Conjugated polymers based on the donor of an asymmetric 5H-dithieno[3,2-b:2′,3′-d]pyran (DTPa) and the acceptors of benzo[d][1,2,3]triazole (BTA) or di-fluorinated benzo[d][1,2,3]triazole (ffBTA) with thiophene as π-bridge were designed and synthesized. Two asymmetric-building-block-containing polymers (ABC-polymers) possess a strong and broad absorption in the range of 300–750 nm and medium optical bandgap of 1.73 and 1.77 eV for PDTPa-TBTA and PDTPa-TffBTA, respectively. Polymer solar cells using PDTPa-TBTA as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor exhibited power conversion efficiencies (PCE) of 2.22% with a Voc of 0.58 V, a Jsc of 6.04 mA/cm2, and an FF of 63.41%. The introduction of fluorine substituents on the BTA unit evidently influenced the optical and photovoltaic properties. Interestingly, although the HOMO energy level indeed decreased, PDTPa-TffBTA showed a decreased Voc of 0.52 V in solar cells. Combined with an obviously enhanced Jsc of 10.23 mA/cm2, and an outstanding FF of 0.64, the PCE of solar cells based on PDTPa-TffBTA was improved by nearly 55%, reached 3.43%. Our results indicate that the BTA unit can be used to construct ABC polymers with a medium bandgap, and the introduction of fluorine on the BTA unit is also effective in improving the photovoltaic performance.
Highlights
Over the past few decades, polymer solar cells (PSCs), given the advantages of a low cost, a light weight, and flexibility, have attracted extensive attention for the generation of affordable, clean, and renewable energy [1]
Our results indicate that the BTA unit can be used to construct ABC polymers with a medium bandgap, and the introduction of fluorine on the BTA unit is effective in improving the photovoltaic performance
(P3HT) [10,11,12,13], people have believed that photovoltaic polymers with great promise should be region-regular, so symmetric building blocks have played a dominant role in the design and synthesis of D–A type polymer photovoltaic materials
Summary
Over the past few decades, polymer solar cells (PSCs), given the advantages of a low cost, a light weight, and flexibility, have attracted extensive attention for the generation of affordable, clean, and renewable energy [1]. Some effective asymmetrical building blocks have developed gradually to construct promising photovoltaic polymers, such as poly [[4,8-bis-[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b0 ]dithiophene-2,6-diyl][3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl]] (PTB7) and its analogues, with the best power conversion efficiency over 10% [14,15,16]. This made people realize that the lack of enough attention. Compared to the the prominent analogue benzothiadiazole (BTs), derivatives (BTs), BTA-based polymers provide advantage of facilederivatives incorporation of provide the prominent advantage of facile incorporation of solubilizing alkyl solubilizing alkyl chains onto the acceptor unit, rather than on the thiophene π-bridge.
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