Characterization of sensitized solar cells based on nanocomposites of protoporphyrin IX and microwave reduced graphene oxide quantum dots

Abstract

In this research we are reporting for the first time the elaboration y characterization of titanium dioxide sensitized solar cells based on nanocomposites of protoporphyrin IX and microwave reduced graphene oxide quantum dots. Reduced graphene oxide quantum dots were synthesized by microwave assisted cutting of reduced graphene oxide and mixed with protoporphyrin IX previous to be drop-casted on titanium dioxide. Characterization was done by dynamic light scattering, ultraviolet visible spectroscopy, Raman spectroscopy, atomic force microscopy, field electron scanning electron microscopy, impedance spectroscopy and current voltage measurements. There were blue and red shifts of Raman and absorption bands of protoporphyrin+reduced graphene oxide quantum dots nanocomposites, evidencing strong interactions because of π−π electrons stacking, this fact was confirmed by microscopy images showing full coverage of protoporphyrin surface by reduced graphene oxide quantum dots. Electrical characterization of titanium dioxide+protoporphyrin+reduced graphene oxide quantum dots showed one of the highest photo-responses and lowest resistivities, in line with impedance measurements in which these composites presented up to ∼200% increase in capacitance, versus TiO2 alone. Efficiency of the optimized cell was 6.13 %, this was a value 9.4 % higher versus titanium dioxide+protoporphyrin cell. The reasons for the behavior of optimized cells are discussed based on a bands diagram showing the possibility of a rectifier effect and because of the strong affinity between protoporphyrin and reduced graphene oxide quantum dots.