Quantum efficiencies (QEs) of innovative hybrid solar cells fabricated using micro/mesoporous zinc (hydr)oxide and its graphite-based composites sensitized by semiconductor quantum dots (SQDs) are reported. High absorption coefficient of CdSe SQDs and the wide band gap of zinc (hydr)oxide and its composites with graphite oxide (GO) are essential to achieve solar cells of higher QEs. Hybrid solar cells are fabricated from zinc (hydr)oxide and its composites (with 2 and 5 wt.% of graphite oxides, termed as, ZnGO-2 and ZnGO-5, respectively) while using potassium iodide or perovskite as an electrolyte. A two-photon fluorescence (TPF) imaging technique was used to determine the internal structure of the solar cell device. The photocurrent and current-voltage measurements were used to measure short-circuit current and open-circuit voltage to calculate the fill factor and QE of these solar cells. The highest QE (up to ∼10.62% ) is realized for a ZnGO-2-based solar cell using potassium iodide as its electrolyte and the CdSe quantum dot as its sensitizer.
The optical properties of zinc (hydr)oxide and the composites of zinc (hydr)oxide with 2% and 5% graphite oxide were investigated by three spectroscopic techniques: absorption, fluorescence and photocurrent techniques. The obtained energy gaps (from 2.85 eV to 2.95 eV) of the composites were smaller than that for zinc oxide (~3.2 eV) and zinc (hydr)oxide (~3.00 eV). The band gap narrowing of the composite materials is due to presence of defects, less confinement, and larger particles. The bonds between zinc (hydr)oxide lattice and the carbon of graphene phase also contribute to this phenomenon.