Effect of TBPO-capped CdSe nanoparticles concentration on sub-bandgap absorption in poly(3-hexylthiophene) thin films studied by photothermal deflection spectroscopy

• The nanocomposite solution of P3HT:wt% TBPO–CdSe was spin coated onto ordinary glass substrate.
• The optical absorption spectra were studied by UV–vis and PDS techniques.
• The sub-bandgap energies were deduced from Tauc’s law.
• We report an optimum sub-bandgap energy value for P3HT:40% CdSe nanocomposite.

In this work, in a first step we studied the effect of dispersed TBPO-capped CdSe nanoparticles in poly(3-hexylthiophene) matrix on the sub-bandgap absorption spectra. Thus we have used two methods the UV–vis technique and photothermal deflection spectroscopy (PDS). We note that the TBPO-capped CdSe concentration have a significant effect on these spectra. In a second step, we deduced the sub-bandgap energy from the PDS optical absorption spectra using the Tauc’s law. Thereby, the sub-bandgap energy decreases with the TBPO-capped CdSe concentration until an optimum concentration approximately at 40%. As a result, the performance enhancement comes from the formation of the electron pathway by interconnected TBPO-capped CdSe in the P3HT matrix without severe aggregation.