Fullerene Dyad With Supramolecular Induced Effect And Application For Bulk Heterojunction Organic Solar Cells

In this paper, we designed and synthesized a series of fullerene acceptors with longalkoxyl chains, and studied the supramolecular induced effect of fullerene dyad containingpairs of hydrophobic groups(C60and bulk trialkoxybenzene), the influence on the organicsolar cell morphology and the device performance, the main contents and discussions areas follows:1. A kind of fullerene derivative containing trioctyloxybenzene was synthesized. Inthe process of spin-coating of PCBB-C8and P3HT solution, PCBB-C8can induce P3HTto self-organize into P3HT crystallites in the absence of external treatments, due to the freeregion for P3HT chains movement provided by supramolecular self-assembly of PCBB-C8.The optimal active layer morphology with long range order, nanoscaled phase separationand bi-continuous transportation channels was achieved. The Jscof P3HT/PCBB-C8blendfilm without thermal annealing is similar with that of P3HT/PCBM with thermal annealingprocess. The photovoltaic device based on as-cast P3HT/PCBB-C8blend film exhibitedexcellent performance with a power conversion efficiency (PCE) of2.4%.2. In order to study the influence of fullerene derivatives with varied alkoxyl chainlength on the supramolecular induced effect, blend film morphology and photovoltaicperformance, we synthesized a series of fullerene derivatives: PCBB-Cn (n=4,6,8,10,12).PCBB-Cn (n=4,6,8,10,12) exhibited similar thermal and electrochemical properties. Allthe fullerene derivatives can induce P3HT to self-organize into P3HT crystallites bysupramolecular self-assembly, and then form ideal active layer morphology. At the sametime, we studied the relationship between the supramolecular induced effect, P3HT crystalsize, blend film morphology and device performance: in the case of P3HT/PCBB-Cn (n=4,6) where alkoxyl chain length was short, the crystallization of P3HT was not sufficient, themorphology was smooth and the device performance was poor; For P3HT/PCBB-C8, thecrystallinity of P3HT increased efficiently, the short current and the device performancewere both the best; When the alkoxyl chain lengths were increased to10and12, thecrystallinity of P3HT in the blend films was still very high, however, the deviceperformance deteriorated. 3. Moieties containing fluorine possess stronger electron-withdrawing ability andrigidity which can efficiently tune the electrochemical properties of fullerene derivativesand enhance the intermolecular interaction. We synthesized a series of fullerene derivativeswith varied numbers of fluorine: nF-PCBB-C8(n=1,3,5), and studied the influence offluorine on the fullerene property, blend film morphology and photovoltaic performance.The electrochemical results indicated that the introduction of fluorine lowered the LUMOenergy levels of fullerene derivatives; the optical and X-ray scattering results proved thatnF-PCBB-C8can also induce P3HT to crystallize. Atomic force microscope (AFM) andoptical microscope (OPM) results showed that P3HT/nF-PCBB-C8blend films formedobvious aggregation, which destroyed the ideal morphology for exciton dissociation andtransport, and result in poor device performance.