Role of Triplet-State Shelving in Organic Photovoltaics: Single-Chain Aggregates of Poly(3-hexylthiophene) versus Mesoscopic Multichain Aggregates

TL;DR

This study investigates the role of triplet excitons in P3HT polymer aggregates, revealing their quenching by intermolecular interactions and differences between single-chain and multi-chain aggregates in photoluminescence behavior.

Contribution

It provides new insights into triplet exciton dynamics in P3HT aggregates, highlighting the effects of aggregate size and structure on photoluminescence and triplet quenching mechanisms.

Findings

Multi-chain aggregates show weaker interchain excitonic coupling.

Triplet excitons are quenched by intermolecular interactions in bulk P3HT.

Solvent vapor annealing enables controlled growth of P3HT aggregates.

Abstract

Triplet excitons have been the focus of considerable attention with regards to the functioning of polymer solar cells, because these species are long-lived and quench subsequently generated singlet excitons in their vicinity. The role of triplets in poly(3-hexylthiophene) (P3HT) has been investigated extensively with contrary conclusions regarding their importance. We probe the various roles triplets can play in P3HT by analyzing the photoluminescence (PL) from isolated single-chain aggregates and multi-chain mesoscopic aggregates. Solvent vapor annealing allows deterministic growth of P3HT aggregates consisting of ~20 chains, which exhibit red-shifted and broadened PL compared to single-chain aggregates. The multi-chain aggregates exhibit a decrease of photon antibunching contrast compared to single-chain aggregates, implying rather weak interchain excitonic coupling and energy transfer. Nevertheless, the influence of triplet-quenching oxygen on PL and a photon correlation analysis of aggregate PL reveal that triplets are quenched by intermolecular interactions in the bulk state.