Ultrafast Exciton Dissociation and Long-Lived Charge Separation in a Photovoltaic Pentacene MoS2 van der Waals Heterojunction

TL;DR

This study demonstrates ultrafast exciton dissociation and long-lived charge separation in a pentacene-MoS2 heterojunction, highlighting its potential for efficient photovoltaic and optoelectronic devices.

Contribution

It provides detailed kinetic analysis of charge transfer in mixed-dimensional heterojunctions, revealing rapid hole transfer and extended charge-separated states.

Findings

Hole transfer occurs in 6.7 ps

Charge-separated state lasts 5.1 ns

50% transfer yield with defect trapping

Abstract

Van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed dimensional p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS2 (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene-MoS2 p-n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS2 excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS2 decay processes, the hole transfer yield from MoS2 to pentacene is found to be approximately 50 percent, with the remaining holes undergoing trapping due to surface defects. Overall, the ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS2 p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.