Photon-absorbing charge-bridging states in organic bulk heterojunctions consisting of diketopyrrolopyrrole derivatives and PCBM

Abstract

We have investigated the photo- and electrochemical properties of five diketopyrrolopyrrole (DPP) derivatives both experimentally and theoretically. In the experimental study, we found that a blend of a DPP derivative named D2 and phenyl-C61-butyric acid methyl ester (PCBM) exhibits the highest internal quantum efficiency (IQE) and power convergence efficiency (PCE) among the five derivatives investigated. In the theoretical study, we found that the open-circuit voltage can be estimated from the difference between the energy gap of frontier orbitals and the voltage loss and that the latter is suppressed when the IQE is large. Then, to investigate the factors that influence the IQE, investigations on charge recombination, hole transfer, and charge transfer induced by photoabsorption were conducted for the complexes of each DPP derivative and PCBM. It was found that D2/PCBM exhibits the largest charge-bridging upon photoabsorption, which leads to the highest IQE and PCE among the five DPP derivatives.

Investigations on the charge transfer mechanism at donor/acceptor interfaces in the quest for descriptors of organic solar cell performance

“…It can be seen that the EQE and JSC becomes larger as ∆Q, dCT, and ∆μD/A increase (in particular, the PTB7/PC71BM system is better than the PTBF2/PC71BM system). This agrees with the observation from [7,8] that ∆μD/A increases as the EQE increases. This comparative examination indeed indicates that ∆Q, dCT, and ∆μD/A rather than ∆μD are a good "descriptor" for assessing the donor quality contributing to solar cell performance.…”

“…They showed that an internal dipole moment along the polymer chain is critical in maintaining the pseudo-charge-transfer characteristics comparing the PCEs of PBB3 and PTB7 copolymers, which have smaller and larger dipole moments, respectively; the latter have larger PCE and JSC compared with the former. On the other hand, we have confirmed by experiments and quantum chemistry calculations on the photophysical and electrochemical properties of complexes of diketopyrrolopyrrole-based donors and a PCBM acceptor that intermolecular charge transfer in the D/A complexes (∆μD/A) rather than ∆μD plays a crucial role in determining solar cell efficiency [8,9].…”

“…Recent studies have focused on the importance of the variation in dipole moments for efficient charge generation [6][7][8][9]. Yu et al have suggested that the variation in dipole moments in intramolecular charge transfer in the donor molecule (denoted as ∆μD) is crucial in controlling PCE [6,7].…”

Theoretical rationalization for reduced charge recombination in bulky carbazole‐based sensitizers in solar cells

“…These results suggest that electronic excitation of these dye–TiO 2 systems directly induces electron injection into the TiO 2 surface. Such excitations inducing direct charge transfer have been known to affect not only DSCs but also organic thin film solar cells …”

Rational Design of Low-Band Gap Star-Shaped Molecules With 2,4,6-Triphenyl-1,3,5-triazine as Core and Diketopyrrolopyrrole Derivatives as Arms for Organic Solar Cells Applications

“…As showing Figure 1, the calculated λ abs value obtained at PBE0 (543 nm) level provided better agreement with the experimental value (523 nm) (Shiau et al, 2015) than those obtained with other levels of theory, with the deviation being 20 nm. Although B3LYP appeared adapted to 1,3,5-triazine and DPP derivatives in literature (Feng et al, 2014; Vala et al, 2014; Jin, 2015; Jin and Irfan, 2015; Jin and Xiao, 2015; Fujii et al, 2016), the λ abs value obtained at the B3LYP/6-31G (d,p) level is worsen accordance with the experimental data (the deviation is 48 nm) than that for at the PBE0/6-31G (d,p) level (the deviation is 20 nm). Additionally, we also calculated the FMOs energy levels of molecule 1 using both at PBE0 and B3LYP methods.…”