Optical studies of melanin films as a material for solar light absorbers

TL;DR

This paper explores the optical and electrical properties of melanin films derived from natural sources, highlighting their potential as light-absorbing materials for solar energy conversion.

Contribution

It provides detailed characterization of melanin films' optical and electrical properties, revealing their suitability for photovoltaic applications and insights into their molecular structure.

Findings

Melanin films have an optical band gap of 1.7 eV.

They exhibit high ultraviolet absorption coefficients.

The films are hydrophilic with stable electrical parameters.

Abstract

This study investigates optical and electrical properties of thin melanin films self-organized grown from water solutions of eumelanin extracted from edible plants. The melanin films exhibit the characteristics of a transparent low conductive polymer with stable in time electrical parameters. The films demonstrate indirect allowed optical transitions, an optical band gap E_g = 1.7 eV and a phonon energy {\hbar \omega} = 0.185 eV as well as a high absorption coefficient in the ultraviolet range, which highlight the film potential for applications as light-absorbing layers in photovoltaic solar energy converters. Analysis of infrared transmission spectra evidences presence of a significant amount of OH groups in the films, pointing to their hydrophilicity, which may have an effect on the film electrical conductivity. It is hypothesized as well that the ratio of sp^3 to sp^2 hybridized CH_n bonds influences the films' optical and electrical properties and that higher concentration of the sp^2 bonds may increase the conductivity due to the enhanced {\pi}-electron delocalization.