On the Understandings of Dielectric Constant and Its Impacts on the Photovoltaic Efficiency in Organic Solar Cells

Abstract

Dielectric constant (ε) is an important parameter affecting the power conversion efficiency of organic solar cells (OSC). Increasing ε of bulk heterojunctions in general can benefit the performance of OSCs, as an increased ε will reduce the influence of Coulomb interaction between weakly bound electron‐hole pairs on charge‐transfer states or bimolecular recombination involving mobile carriers to reduce geminate and nongeminate losses. In this review, we overview the current understandings on dielectric constant and its impacts on exciton dissociation and voltage losses in OSCs and summarize recent efforts attempting to modify the dielectric properties of OSC materials through synthetic approaches. We further discuss the commonly adopted techniques for determining the parameter of ε with stressing the testing conditions that may affect the accuracy of results. At last, we suggest that novel experimental methods to improve the dielectric constant and resultant physical processes in OSCs will be appreciated, which helps enrich the existing strategy reservoir toward enhancement of photovoltaic efficiencies.

Asymmetric Glycolated Substitution for Enhanced Permittivity and Ecocompatibility of High-Performance Photovoltaic Electron Acceptor

“…Because of the higher ε r and the more balanced charge-carrier transport, PM6:Y6-4O exhibited a smaller bimolecular recombination coefficient, which can notably reduce the charge recombination and further lead to a higher J SC . According to the previous work, the decreased bimolecular recombination loss related to a larger dielectric constant can play an important role in lowering the open-circuit voltage loss ( V loss ) of OSC devices, which is defined as the difference between the E g PV / q and the V OC . , PM6:Y6-4O-based devices exhibited a smaller V loss of 0.57 V relative to PM6:Y6-based devices ( V loss = 0.59 V). The larger dielectric constant of Y6-4O leads to a smaller V loss of PM6:Y6-4O based devices, which is beneficial for the higher V OC and PCE.…”

Triplet exciton formation for non-radiative voltage loss in high-efficiency nonfullerene organic solar cells

“…Therefore, triplet exciton formation from CT exciton relaxation is suppressed with donor side-chain fluorination. 39,[59][60][61] On the other hand, AFM images (Figure S18) show that the root-mean-square surface roughness of PBDB-T:IXIC-4Cl is larger (1.73 nm) than that of PM6:IXIC-4Cl (1.25 nm). GIWAXS and SCLC results show that blend film with fluorinated PM6 exhibits slightly better p-p stacking and higher carrier mobility, which can help CT exciton delocalization and free carrier extraction.…”

Fine-Tuning the Dipole Moment of Asymmetric Non-Fullerene Acceptors Enabling Efficient and Stable Organic Solar Cells

“…It is well known that the large dipole moment usually can induce a higher relative dielectric constant and stronger intermolecular interaction. The higher relative dielectric constant may reduce the exciton binding energy and reduce the charge recombination losses. − Usually, a stronger intermolecular interaction means closer packing of organic semiconductors, which is beneficial for charge transport − and device stability. , Thus, high-performance asymmetric SMAs are anticipated by modifying A-DA′D-A-type SMAs. In our earlier work, a new asymmetric A-D 1 A′D 2 -A-type acceptor named as TB-4Cl (as shown in Scheme ) has been synthesized .…”