Researchers from NJIT (New Jersey Institute of Technology, New Jersey, USA) in collaboration with researchers from CSIR-CECRI (Central Scientific Industrial Research Institute - Central Electrochemical Research Institute, Tamil Nadu, India) have fabricated a new kind of dye sensitized solar cells (DSSC) based on zinc oxide-graphene (ZnO-G) composites, having a flake like morphology. The polyol approach used for synthesis of the composite material can be envisioned for future low-cost, transparent and flexible solar cells that will be installed on surfaces including windows, roofs in the near future.
The novel technique for the fabrication has been developed by a 3rd year Ph.D. student Moab Rajan Philip and Dr. Hieu P Nguyen, Assistant Professor in the Electrical and Computer Engineering Department of NJIT and is reported in Current Nanomaterials-Bentham Science Publishers. The paper is co-authored by Rupesh K Babu, V. Krishnakumar and T. Bui who are researchers in CSIR-CECRI and NJIT respectively.
Zinc Oxide (ZnO) is a multifunctional semiconductor material that can be fabricated at low temperatures. The wide energy bandgap, radiation resistance, high chemical stability, and high excitation binding energy leads to ZnO offering huge potential in applications involving sensors, light-emitting diodes (LEDs), piezoelectric devices, solar cells, short wavelength lasers and transistors. In addition, ZnO offers superior electrical and optical properties that include high electron mobility in the order of 1500 cm2V-1s-1 at room temperature, a wide band gap energy of 3.3 eV and a high exciton (electron-hole) binding energy of 60 meV. Graphene, which is one of the most exciting 2D materials known to man, exhibits superior properties such as ultrahigh electron mobility, large surface area, high chemical and thermal stability, excellent electrical and optical properties. The ZnO-G composites exhibited in the study significantly enhanced photoluminescence which was around 8 times stronger than that of ZnO samples, attributed to the contribution of plasmonic effect of graphene in ZnO-G. It has been reported that the drawback of poor catalytic activity in ZnO due to its photoelectron recombination is known can be overwhelmed by the incorporation of graphene into ZnO matrix thereby improving its photodegradation efficiency and reducing photoelectron recombination. The latter reasons along with the ZnO-G composite's photosensitivity, electron transport capability, chemical stability and better light adsorption make it an interesting material for the future era electronic devices.
"We've demonstrated that devices based on ZnO-G have an excellent conversion efficiency compared to ZnO"- Moab and Prof. Nguyen (lead authors of the paper) says. The conversion efficiency of ZnO-G DSSCs is greatly increased compared to that of the bare ZnO devices which are 0.438% and 0.067%, respectively. Moreover the authors add that the low-cost polyol process, in addition to being simple and facile, do have the benefits of being environmentally friendly along with large scale production. The team studied the fabricated samples via characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), laser raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence spectroscopy (PL) and dye sensitized solar cell (DSSC) studies. Moab adds "The initial work is promising and excellent and might pave the way for future investigations into similar material oxide material systems will help us to reach potential long term real applications." Prof. Hieu comments that "The high surface area hexagonal wurtzite ZnO particles thus fabricated by inexpensive and environmentally friendly polyol route can ultimately lead to being used as a suitable anode material in DSSCs as well as an excellent catalyst/adsorbent."
Nguyen H. P. T.; Philip, M.R.; Babu R.; Krishnakumar V.; Bui T. H. Q. Polyol Synthesis of Zinc Oxide-Graphene Composites: Enhanced Dye- Sensitized Solar Cell Efficiency. Current Nanomaterials, 2018, Vol. 03. DOI: 10.2174/2405461503666180507124310