Synthesis and properties of a novel narrow band gap oligomeric diketopyrrolopyrrole-based organic semiconductor

TL;DR

This paper reports the synthesis of a novel narrow band gap oligomeric diketopyrrolopyrrole-based organic semiconductor with promising electronic properties, but highlights challenges in its application in organic photovoltaics due to phase separation issues.

Contribution

It introduces a new oligomeric diketopyrrolopyrrole-based semiconductor and analyzes its electronic properties and limitations in photovoltaic applications.

Findings

HOMO level of -5.34 eV and a band gap of 1.33 eV.

Achieved hole mobility of 1 x 10^-3 cm^2 V^-1 s^-1 after annealing.

OPV devices with this material had a PCE of 0.72%.

Abstract

An oligomeric semiconductor containing three bisthiophenediketopyrrolopyrole units (Tri-BTDPP) was synthesized and characterized. Tri-BTDPP has a HOMO level of -5.34 eV, a broad absorption close to the near infrared region and a low band gap of 1.33 eV. Additionally, a promising hole mobility of 1 x 10-3 cm V-1 s-1 was achieved after thermal annealing at 150 C in organic field effect transistors (OFET). Organic photovoltaic (OPV) cells containing Tri-BTDPP and PC71BM as the donor/acceptor couple exhibited a power conversion efficiency (PCE) of 0.72%. Through an intensive study of the active layer using AFM, XRD, and DSC, it was found that Tri-BTDPP and PC71BM were unable to intermix effectively, resulting in oversized Tri-BTDPP crystalline phases and thus poor charge separation. Strategies to improve the OPV performance were thus proposed.