Elucidating the impact of PbI2 on photophysical and electrical properties of poly(3-hexythiophene)

Abstract

Owing to high absorption coefficient, controlled morphology and high charge carrier mobility, poly (3-hexylthiophene) (P3HT) is a well-known donor material for organic solar cells, but device efficiency is still average compared to other conjugated polymers such as PDCBT, PB3T, P12 etc. The present research aims to enhance the optoelectrical properties of P3HT thin films through the incorporation of PbI2 in P3HT. Herein, novel P3HT/PbI2 hybrid thin films fabricated and the effect of different PbI2 doping levels on structural, spectroscopic and electrical properties of P3HT was elucidated. Incorporation of PbI2 in P3HT matrix was confirmed through the observation of characteristic peaks of PbI2 in XRD and Raman spectra of P3HT. Surface morphology of fabricated films were investigated by SEM and reveals that the morphology of hybrid film entirely changed for higher PbI2 concentration. Fabricated films were then characterized through a number of spectroscopic techniques including: UV–Visible absorption, fluorescence and ellipsometer spectroscopy. The optical parameters: dielectric constant (εr), dielectric loss (εi), extinction coefficient (k) and refractive index (n) were extracted from the fitting of Ellipsometer data by using mathematical models. It was found that the incorporation of PbI2 in P3HT leads to decrease of the optical band gap from 1.94 eV to 1.79 eV and increases of the refractive of P3HT thin films. The effective life time of charge carrier was found to be decreases from 106 ps for pristine P3HT to 15.6 ps for P3HT/PbI2. Hall Effect measurement shows enhancement in carrier concentrations from 7.62 × 1014 cm−3 (pristine P3HT) to 4.51 × 1018 cm−3 (P3HT/PbI2), decrease of electrical resistivity from 3.68 × 104 Ω cm (pristine P3HT) to 1.00 × 104 Ω cm (P3HT/PbI2) and decrease in carrier mobility from 2.23 × 10−1 (pristine P3HT) to 1.38 × 10−3 cm2/Vs (P3HT/PbI2).