Are Transport Models Able To Predict Charge Carrier Mobilities in Organic Semiconductors?

Abstract

Organic photovoltaic devices have been steadily becoming more efficient through a combination of reduction in voltage losses, minimization of recombination pathways, and an increase in dimensionality of charge carrier pathways. However, a transport description that predicts the carrier mobility based on the mechanisms behind charge generation and transport in organic semiconducting material blends has been challenging. The complexity is mainly due to the absence of long-range order and the weak band coupling between molecules. In this Feature Article, we discuss charge transport models through a tight-binding lattice model approach. From the introduction of lattice disorder, we make a correlated liquid metal analogy and describe the effects of disorder on transport with quantum mechanical diffusion, Anderson localization, and percolation. We show that it is possible to understand the high-and lowtemperature mobility data, the factors which limit the mobility, and the nature of the effective mass of charge carriers.

Systematic Merging of Nonfullerene Acceptor π-Extension and Tetrafluorination Strategies Affords Polymer Solar Cells with >16% Efficiency

“…While large intermolecular couplings are not a sufficient condition for more efficient charge transport, all else being equal increased couplings lead to higher mobilities due to higher bandwidth for transport to occur. 69 Note that fluorination has only a minor impact on the coupling strength. The largest electronic coupling |J| = 103.8 meV is observed in BT-L4F, whereas the photovoltaic measurements indicate that tightly bound structures that led to its high coupling can result in reduced solubility and BHJ processing, hence poor cell performance.…”

“…In addition, the π-extension is effective in enhancing intermolecular electronic coupling due to the larger π-overlaps between the extended EGs. While large intermolecular couplings are not a sufficient condition for more efficient charge transport, all else being equal increased couplings lead to higher mobilities due to higher bandwidth for transport to occur . Note that fluorination has only a minor impact on the coupling strength.…”

Fluorinating π‐Extended Molecular Acceptors Yields Highly Connected Crystal Structures and Low Reorganization Energies for Efficient Solar Cells

“…[ 17 ] As seen in charge transport of biomolecules, [ 23,24 ] NFA packing motifs that utilize transport networks with greater dimensionality than 1D exhibit superior performance. [ 25,26 ] Here we use a combined experimental and computational approach to create and characterize new indacenodithienothiophene (IDTT) containing NFAs having both π‐extension [ 17,25 ] ( Figure 1 B) and fluorination [ 17,27,28 ] (Figure 1C). These systems were chosen because of their relevance to the rational design of high‐performing NFAs, as the IDTT core is among the most widely used and highest performing of NFA scaffolds, [ 14 ] with ITIC [ 29 ] (Figure 1D) being the most well‐known example.…”

Simulation of Charge Carriers in Organic Electronic Devices: Methods with their Fundamentals and Applications

“…Note that also descriptions for a coherent motion in a statically disordered energy landscape are emergent. [ 37 ]…”

“…Note that also descriptions for a coherent motion in a statically disordered energy landscape are emergent. [37] For a pair of sites, the likelihood of a transfer is given by a transfer rate, ss w ′ , that takes different formulations depending on the nature of the charge transfer. [38][39][40][41][42] Before giving examples for possible rate formulations, let us first introduce the following notation to record the position of all N cc considered charge carriers: A so-called configuration x stores all hopping sites that are occupied with a charge carrier ( , , , )…”