Effect of Fullerene Tris-adducts on the Photovoltaic Performance of P3HT:Fullerene Ternary Blends

Abstract

Fullerene tris-adducts have the potential of achieving high open-circuit voltages (V(OC)) in bulk heterojunction (BHJ) polymer solar cells (PSCs), because their lowest unoccupied molecular orbital (LUMO) level is higher than those of fullerene mono- and bis-adducts. However, no successful examples of the use of fullerene tris-adducts as electron acceptors have been reported. Herein, we developed a ternary-blend approach for the use of fullerene tris-adducts to fully exploit the merit of their high LUMO level. The compound o-xylenyl C60 tris-adduct (OXCTA) was used as a ternary acceptor in the model system of poly(3-hexylthiophene) (P3HT) as the electron donor and the two soluble fullerene acceptors of OXCTA and fullerene monoadduct (o-xylenyl C60 monoadduct (OXCMA), phenyl C61-butyric acid methyl ester (PCBM), or indene-C60 monoadduct (ICMA)). To explore the effect of OXCTA in ternary-blend PSC devices, the photovoltaic behavior of the device was investigated in terms of the weight fraction of OXCTA (W(OXCTA)). When W(OXCTA) is small (<0.3), OXCTA can generate a synergistic bridging effect between P3HT and the fullerene monoadduct, leading to simultaneous enhancement in both V(OC) and short-circuit current (J(SC)). For example, the ternary PSC devices of P3HT:(OXCMA:OXCTA) with W(OXCTA) of 0.1 and 0.3 exhibited power-conversion efficiencies (PCEs) of 3.91% and 3.96%, respectively, which were significantly higher than the 3.61% provided by the P3HT:OXCMA device. Interestingly, for W(OXCTA) > 0.7, both V(OC) and PCE of the ternary-blend PSCs exhibited nonlinear compositional dependence on W(OXCTA). We noted that the nonlinear compositional trend of P3HT:(OXCMA:OXCTA) was significantly different from that of P3HT:(OXCMA:o-xylenyl C60 bis-adduct (OXCBA)) ternary-blend PSC devices. The fundamental reasons for the differences between the photovoltaic trends of the two different ternary-blend systems were investigated systemically by comparing their optical, electrical, and morphological properties.

Molecular structure-device performance relationship in polymer solar cells based on indene-C60 bis-adduct derivatives

“…The I-V characteristics of the OFETs of the ICBA derivatives are summarized in Table 4. The ICBA devices exhibited an average electron mobility of 3.40×10 −3 cm 2 V −1 s −1 , which agreed well with the previous findings [42]. The average electron mobility of FICBA devices was 9.97×10 −4 cm 2 V −1 s −1 , and the maximum electron mobility (μ e, max = 1.03×10 −3 cm 2 V −1 s −1 ) was comparable to that of the ICBA devices.…”

“…Therefore, systematic study of the effects of the molecular structure of fullerene derivatives on their interaction with conjugated polymers and of their effects on the performances of PSCs is essential to determine the appropriate design of fullerene derivatives for use in PSCs. Such study on the molecular structure-device function relationship in PSCs using the indene-C 60 bis-adducts (ICBA) model is especially important, because ICBA is one of the most studied and successful bis-adduct fullerenes, which produces high V oc and PCE values in PSCs [33,35,42].…”

Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells

“…24,30,31 Therefore, the majority of studies on ternary solar cells have focused on multi-polymer donor:acceptor blends. 19,23,[27][28][29] However, the mixing of two polymers is more complicated due to both a lack of entropic driving force for mixing, and the potential for strong intermolecular attractions between polymer chains. 32 Therefore, a ternary approach, wherein small molecule acceptors are mixed in a donor:multi-acceptor blend (D:A1:A2, where D is donor polymer, A1 is the primary acceptor and A2 is a second acceptor), has the potential to offer morphological advantages.…”

Perspective of a new trend in organic photovoltaic: ternary blend polymer solar cells

“…The cascade like energy levels (shown in Fig. 4) of ternary blend PSCs can facilitate charge transfer at the D/A interface owing to the bridging effect to reduce the energy loss [31,32]. For example, Huang et al [33] reported that by incorporating a small molecule donor 7,7'-{5,5'- [10,12-…”

“…Ternary blend devices with 15% ICBA content exhibit an average PCE of 8.13%, higher than that (7.23%) of the PTB7:PC 71 BM binary blend. Kang et al [32] used fullerene tris-adducts to fully exploit the merit of their high LUMO level. The compound OXCTA was used as a ternary acceptor in the model system of P3HT as the electron donor and fullerene monoadduct as the acceptor.…”