Morphology controlled n-type TiO2 and stoichiometry adjusted p-type Cu2ZnSnS4 thin films for photovoltaic applications

Abstract

This paper presents the fabrication and characterization of stoichiometry adjusted Cu<inf>2</inf>Zn<inf>1.5</inf>Sn<inf>1.2</inf>S<inf>4.4</inf> thin film (FTO/TiO<inf>2</inf>/CdS/CZTS/Au) photovoltaic (PV) devices. The PV devices were developed using the window layer of rutile TiO<inf>2</inf> nanoarchitecture arrays, i.e., one-dimensional (1D) nanorods and three-dimensional (3D) combined/ hierarchical structures (nanorods with microspheres). Onedimensional (1D) nanorods and 3D combined structures of TiO<inf>2</inf> window layers were synthesized by a hydrothermal method with different solvents without any assistance of surfactants and templates. We achieved two kinds of TiO<inf>2</inf> nanostructures by tuning the precursor concentrations and volume by keeping a constant growth time and temperature. The detailed structural properties were studied using X-ray diffraction and high resolution transmission electron microscopy. Phase formation and chemical state of the prepared samples were examined by Raman spectroscopy and X-ray photoelectron spectroscopy. The surface morphology and luminescence studies of TiO<inf>2</inf> nanostructures were analyzed using field emission scanning electron microscopy and cathodoluminescence techniques. The current-voltage performance of fabricated devices were measured under an AM 1.5 solar simulator. It is observed that combined structure PV device shows better efficiency (1.45%) than the nanorods alone structure (0.55%). Present work is a first attempt made to construct the inverted CZTS based solar cells. This study establishes the window layer of hierarchical TiO<inf>2</inf> nanostructures based morphology that offers a great potential for the development of high-efficiency nonstoichiometric CZTS based solar cells. © 2017 American Chemical Society.