Primary Photoexcitations and the Origin of the Photocurrent in Rubrene Single Crystals

TL;DR

This study investigates how photoexcitations in rubrene single crystals lead to photocurrent, revealing the roles of free excitons, vibronic states, and molecular excitons across different photon energies.

Contribution

It demonstrates the excitation pathways of free excitons and their relation to photocurrent generation in rubrene crystals, highlighting energy-dependent mechanisms.

Findings

Free excitons are photoexcited above 2.0 eV.

Competition between free exciton and vibronic state excitation.

Long-lived intermediate state creates free carriers below 2.25 eV.

Abstract

By simultaneously measuring the excitation spectra of transient luminescence and transient photoconductivity after picosecond pulsed excitation in rubrene single crystals we show that free excitons are photoexcited starting at photon energies above 2.0 eV. We observe a competition between photoexcitation of free excitons and photoexcitation into vibronic states that subsequently decays into free carriers, while molecular excitons are instead formed predominantly through the free exciton. At photon energies below 2.25 eV, free charge carriers are only created through a long-lived intermediate state with a lifetime of up to 0.1 ms and no free carriers appear during the exciton lifetime.