Diketopyrrolopyrrole-Based π-Bridged Donor–Acceptor Polymer for Photovoltaic Applications

Abstract

We report the synthesis, properties, and photovoltaic applications of a new conjugated copolymer (C12DPP-π-BT) containing a donor group (bithiophene) and an acceptor group (2,5-didodecylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione), bridged by a phenyl group. Using cyclic voltammetry, we found the energy levels of C12DPP-π-BT are intermediate to common electron donor and acceptor photovoltaic materials, poly (3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), respectively. Whereas P3HT and PCBM are exclusively electron donating or accepting, we predict C12DPP-π-BT may uniquely serve as either an electron donor or an acceptor when paired with PCBM or P3HT forming junctions with large built-in potentials. We confirmed the ambipolar nature of C12DPP-π-BT in space charge limited current measurements and in C12DPP-π-BT:PCBM and C12DPP-π-BT:P3HT bulk heterojunction solar cells, achieving power conversion efficiencies of 1.67% and 0.84%, respectively, under illumination of AM 1.5G (100 mW/cm(2)). Adding diiodooctane to C12DPP-π-BT:PCBM improved donor-acceptor inter-mixing and film uniformity, and therefore enhanced charge separation and overall device efficiency. Using higher-molecular-weight polymer C12DPP-π-BT in both C12DPP-π-BT:PCBM and C12DPP-π-BT:P3HT devices improved charge transport and hence the performance of the solar cells. In addition, we compared the structural and electronic properties of C12DPP-π-BT:PCBM and C12DPP-π-BT:P3HT blends, representing the materials classes of polymer:fullerene and polymer:polymer blends. In C12DPP-π-BT:PCBM blends, higher short circuit currents were obtained, consistent with faster charge transfer and balanced electron and hole transport, but lower open circuit voltages may be reduced by trap-assisted recombination and interfacial recombination losses. In contrast, C12DPP-π-BT:P3HT blends exhibit higher open circuit voltage, but short circuit currents were limited by charge transfer between the polymers. In conclusion, C12DPP-π-BT is a promising material with intrinsic ambipolar characteristics for organic photovoltaics and may operate as either a donor or acceptor in the design of bulk heterojunction solar cells.

Imide- and Amide-Functionalized Polymer Semiconductors

“…BHJ all-polymer cells having the structure ITO/ PEDOT:PSS/P3HT:P297/LiF/Al show a moderate PCE of 0.84% with a J sc of 2.6 mA/cm 2 and a V oc of 0.92 V. When combined with PCBM, the P297:PCBM cells show a PCE of 1.67%. 393 The result demonstrates that P297 can be used as either a donor or acceptor semiconductor, depending on the choice of another component, which is in good agreement with its FMOs and ambipolar transport characteristics. 393 Other phenyl-flanked DPP-based polymers P298 and P299 are incorporated into solar cells as acceptor semiconductors.…”

“…394 Cyclic voltammetry shows that P297 has a LUMO of −3.5 eV, which is 0.4 eV lower than that of p-type P3HT. 393 The combination of P3HT:P297 shows some degree of photoluminescence quenching, which indicates charge transfer from P3HT to P297. 393 SCLC measurements reveal that P297 has a μ e of 4.7 × 10 −5 cm 2 /(V s).…”

“…393 The combination of P3HT:P297 shows some degree of photoluminescence quenching, which indicates charge transfer from P3HT to P297. 393 SCLC measurements reveal that P297 has a μ e of 4.7 × 10 −5 cm 2 /(V s). BHJ all-polymer cells having the structure ITO/ PEDOT:PSS/P3HT:P297/LiF/Al show a moderate PCE of 0.84% with a J sc of 2.6 mA/cm 2 and a V oc of 0.92 V. When combined with PCBM, the P297:PCBM cells show a PCE of 1.67%.…”

Techniques for characterization of charge carrier mobility in organic semiconductors

“…As the required thickness of the sample is similar to that used for the active layer in BHJSCs, many researchers use this technique for charge-carrier mobility measurements. [65][66][67] However, a charge injection contact is critical for SCLC. These techniques cannot be used to measure hole mobility for organic semiconductors with very low HOMO level, or measure electron mobility with very high LUMO level.…”

Polymer design for solar cell – Current trend and future scenario

“…À1 s À1 and electron mobility of 4.7 Â 10 À5 cm 2 V À1 s À1 . P134:PCBM and P134:P3HT bulk heterojunction solar cells gave PCE's of 1.67% and 0.84%, respectively[127]. Another ambipolar polymer (P135) synthesised from thieno[3,2-b]thiophene diketopyrrolopyrrole and benzo[1,2-b:4,5-b 0 ]dithiophene having thienothiophene linker.…”