Steady-state photoconductivity and multi-particle interactions in high-mobility organic semiconductors

Abstract

Fundamental understanding of photocarrier generation, transport and recombination under a steady-state photoexcitation has been an important goal of organic electronics and photonics, since these processes govern such electronic properties of organic semiconductors as, for instance, photoconductivity. Here, we discovered that photoconductivity of a highly ordered organic semiconductor rubrene exhibits several distinct regimes, in which photocurrent as a function of cw (continuous wave) excitation intensity is described by a power law with exponents sequentially taking values 1, 1/3 and ¼. We show that in pristine crystals this photocurrent is generated at the very surface of the crystals, while the bulk photocurrent is drastically smaller and follows a different sequence of exponents, 1 and ½. We describe a simple experimental procedure, based on an application of “gauge effect” in high vacuum, that allows to disentangle the surface and bulk contributions to photoconductivity. A model based on singlet exciton fission, triplet fusion and triplet-charge quenching that can describe these non-trivial effects in photoconductivity of highly ordered organic semiconductors is proposed. Observation of these effects in photoconductivity and modeling of the underlying microscopic mechanisms described in this work represent a significant step forward in our understanding of electronic properties of organic semiconductors.

Experimental Demonstration of Correlated Flux Scaling in Photoconductivity and Photoluminescence of Lead-Halide Perovskites

“…have been in fact observed in rubrene molecular crystals (47). The microscopic mechanism leading to this behavior in rubrene is, however, qualitatively different from this model, because it was experimentally shown to lead to an exclusively surface photoconductivity in pristine rubrene, while this model appeals to bulk photoconduction.…”

High-Detectivity Perovskite Light Detectors Printed in Air from Benign Solvents

“…Moreover, with addition of PCBM, the photocurrent is a power law of light intensity, i.e., f I a with a z 0.7, on the basis of which it is possible to retrieve the input light signal from the recorded photocurrent. [40][41][42] In a photoconductor, the gain originates from a strong unbalance in the transport properties of the photogenerated holes and electrons following the absorption of a photon, where one of the two carriers is deeply trapped and the other can drift under the external field. 38,39 Once the mobile carrier is collected at the electrode, another carrier is injected for charge neutrality.…”

Highly Efficient Rubrene–Graphene Charge‐Transfer Interfaces as Phototransistors in the Visible Regime

“…This observation demonstrates that the high charge carrier mobility in graphene plays an essential role for efficient transport of photo-excited holes between source and drain electrodes whereas the surface photoconductivity of rubrene [23] does not significantly contribute towards read-out signals.…”