Localization-dependent charge separation efficiency at an organic/inorganic hybrid interface

TL;DR

This study investigates how charge separation efficiency at an organic/inorganic hybrid interface depends on the localization of excited states, revealing that specific states facilitate or hinder charge transfer.

Contribution

It provides a detailed understanding of the relaxation processes and identifies the states responsible for efficient charge separation at the hybrid interface.

Findings

Only the lowest energy state on the organic molecule efficiently separates charge.

A long-lived triplet state acts as a sink, reducing charge separation efficiency.

Different localized states have distinct relaxation pathways affecting overall performance.

Abstract

By combining complementary optical techniques, photoluminescence and time-resolved excited state absorption, we achieve a comprehensive picture of the relaxation processes in the organic/inorganic hybrid system SP6/ZnO. We identify two long-lived excited states of the organic molecules of which only the lowest energy one, localized on the sexiphenyl backbone of the molecule, is found to efficiently charge separate to the ZnO conduction band or radiatively recombine. The other state, most likely localized on the spiro-linked biphenyl, relaxes only by intersystem crossing to a long-lived, probably triplet state, thus acting as a sink of the excitation and limiting the charge separation efficiency.