Pressure dependence of singlet and triplet excitons in amorphous polymer semiconductors

¹ Department of Physics and Astronomy, University of Missouri - Columbia, MO 65211, USA
² Solid State and Structural Chemistry Unit, Indian Institute of Science - Bangalore 560012, India
³ Bergische Universität Wuppertal, Makromolekulare Chemie - Wuppertal, Germany

^(b) guhas@missouri.edu (corresponding author)

Received: 19 August 2013
Accepted: 16 October 2013

Abstract

We present optical studies of both singlet and triplet states of a ladder-type conjugated polymer as a function of hydrostatic pressure. The pressure coefficient of the triplet-triplet absorption is smaller compared to the pressure coefficient of the singlet excitation, highlighting the more localized nature of triplet excitons. The photoluminescence and phosphorescence energies red-shift at similar rates with increasing pressure, thus giving experimental evidence for the first time that the singlet-triplet splitting remains almost a constant under high pressure until 4 GPa. The diffusion length of the triplet excitons decreases to a few hundred nm at high pressures, as compared with a few micrometers at atmospheric pressure.