Tuning the charge flow between Marcus regimes in an organic thin-film device

Abstract

Marcus’s theory of electron transfer, initially formulated six decades ago for redox reactions in solution, is now of great importance for very diverse scientific communities. The molecular scale tunability of electronic properties renders organic semiconductor materials in principle an ideal platform to test this theory. However, the demonstration of charge transfer in different Marcus regions requires a precise control over the driving force acting on the charge carriers. Here, we make use of a three-terminal hot-electron molecular transistor, which lets us access unconventional transport regimes. Thanks to the control of the injection energy of hot carriers in the molecular thin film we induce an effective negative differential resistance state that is a direct consequence of the Marcus Inverted Region.

Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers

“…4a to illustrate the effect on the CT rates). We also note that the inverted region (decrease in rate upon increase in driving force) is experimentally not observed for the HT and ET rates, which can be mainly assigned to the broadness of the MLJ rate spectrum 55 . The absence of the Marcus inverted region for polymer:fullerene blends has also been attributed to the fact that sub-100 fs rates are too fast to be described within the Marcus formalism for non-adiabatic ET, warranting a description in the adiabatic limit [30][31][32][33] .…”

Reorganization Energy upon Controlled Intermolecular Charge‐Transfer Reactions in Monolithically Integrated Nanodevices

“…from the Marcus to the inverted Marcus region) may take place as a function of the chemical structure, molecular orbital gating, or voltage bias polarity. [19][20][21] Notably, the reliable assessments of λ were crucial in all these investigations, ensuring materials function adjustability and providing a precise description of the role played by T and E in the performance of thin-film-based devices, [20] molecular diodes, [21] and single-molecule transistors. [19] In our scheme to assess λ using nCap, the semiclassical Marcus theory (i.e., at high T and high E regimes) allowed us to address an ultimate challenge, which regards a direct consequence of the nanometer-length transport distance.…”

“…temperature-dependent charge transport measurements. [18][19][20][21] Within this frame the charge-transfer kinetics via non-coherent hopping allows full charge-carrier relaxation and nuclear reorganization within the molecules and their surrounding units. As we shall see, this defines the Marcus reorganization energy λ, a pivotal parameter in the charge-transfer activation energy determination.…”

Charge transfer state characterization and voltage losses of organic solar cells

“…The reason for the decreasing transition rate is the fact that transitions need to occur at a reaction coordinate smaller than the equilibrium coordinate for both the initial and final state. The MIR has been challenging to verify experimentally [85], though recent work showed the impact of the interfacial driving force on CT processes in thin-film polymer blends [81,86], quantified the reorganization energy for photoinduced electron transfer in the MIR of a carbon nanotube heterojunction [87], and investigated charge transport in transistors based on thin film small molecules [85] and molecular junctions based on self-assembled monolayers [88]. The highest transition rate occurs for systems where ∆G 0 = λ (case 3 in figure 4(b)) and the potential energy parabolas of the states intersect at the equilibrium reaction coordinate of the initial state.…”