Reports: AC10
48683-AC10 Materials and Architectures for Highly Efficient Photoelectrochemical Solar Cell Devices
Objective of this project is to develop novel architectures for photoelectrochemical solar cells made using wet chemistry methods and common, inexpensive, non toxic materials, that would provide for improved light absorption and enhanced efficiency.
In particular, this effort will focus on the synthesis of titania (a semiconductor with band gap of ~ 3.2 eV) nanotubes, combined with Copper oxide Cu2O (a semiconductor with band gap of ~ 2.1 eV), to enhance light absorption.
In this first year the master student involved has mastered methods to grow titania nanotubes by electrochemical anodization, annealed the nanotubes to crystallize the titania, and developed a reliable method to electrodeposit copper oxide within and outside the nanotubes. Pretreatment of the titania and deposition parameters are being optimized to control deposition within or outside the nanotubes.
The titania nanotubes and the Cu2O/TiO2 assemblies are characterized by Raman spectroscopy, X-ray diffraction, and scanning electron microscopy.
The conductivity of the titania nanotubes increases upon crystallization in the anatase phase. Conductivity is further improved at the bottom of the tubes by electrochemical reduction (Macak, Adv Mater 19, 3027 (2007)), facilitating the electrodeposition process.
Both n- and p-type Cu2O can be obtained by using different electrolyte chemistries. The photoelectrochemical behavior of Cu2O deposited on metal substrates or on titania nanotubes was measured in alkaline (KOH) and neutral (Na2SO4) solutions. Cu2O tends to crystallize when immersed in these solutions in presence of UV light. Correspondingly, its electrochemical stability tends to improve; however the electrochemical window of stability is limited.
Efforts are now directed towards the controlled electrochemical synthesis of Fe2O3, another semiconductor with band gap ~ 2 eV, which should however exhibit a better electrochemical stability. In a parallel effort to fabricate titanium oxide with high surface area, an undergraduate summer student started working with nanoporous gold, a bicontinuous structure consisting of voids and ligaments with dimensions of the order of 10 – 50 nm, and has developed a method to conformally coat the Au surface with titania by using sol-gel method. Characterization of the photoelectrochemical response of this structure with respect to smooth titania is currently ongoing.
