Efficiency Enhancement of Betanin-Chlorophyll Cosensitized Natural Pigment Solar Cells Using Plasmonic Effect of Silver Nanoparticles

This article investigates efficiency improvement of a betanin-chlorophyll cosensitized solar cell using silver nanoparticles (AgNPs) exhibiting localized surface plasmon resonance (LSPR). In this solar cell, betanin is the main contributing natural pigment absorbing in the green wavelength region, and chlorophyll is the complementary pigment absorbing in the blue and red portions of the solar spectrum. Finite-difference time-domain simulations were performed to choose the optimal dimension of AgNPs such that their LSPR wavelength coincides with the absorption band of betanin. Wavelength-dependent scattering response of the AgNPs was studied at sizes 20-100 nm, and the simulations showed that 60-nm AgNPs exhibit plasmon-enhanced scattering at a wavelength matching the absorption peak of betanin (lambda similar to 540 nm). Electric field profiles were studied at the ON and OFF resonant wavelengths demonstrating greater than ten times field enhancement at resonance. Optimally sized AgNPs were synthesized and incorporated into the photoanodes, and spectroscopic studies confirmed plasmonic enhancement in absorption by betanin. The performances of the betanin solar cell and betanin-chlorophyll cosensitized solar cells were assessed with and without the inclusion of AgNPs. The plasmon-enhanced betanin solar cell gave a maximum efficiency of 0.658 +/- 0.026% compared with 0.538 +/- 0.02% by the pristine counterpart. A maximum efficiency of 0.793 +/- 0.009% was achieved by the plasmon-enhanced betanin-chlorophyll cosensitized solar cell compared with 0.612 +/- 0.019% by the pristine counterpart. The 20% enhancement of efficiency is attributed to enhanced absorption by betanin because of the LSPR effect of the AgNPs, resulting in an improved current generation in the plasmonic solar cells. Electrochemical impedance spectroscopy and photoluminescence studies confirmed that the AgNP incorporation also resulted in improved electron lifetime, charge transfer, and reduced electron recombination.