Research

    Our research involves two different but strongly connected areas:
1. Solution deposition of semiconductor films.
2. Nanoporous, semiconductor-sensitized solar cells (both solid state and liquid junction).

 

Solution deposition of semiconductor films

A common thread running through the groups work almost since its inception is the deposition of semiconductor films from solution. The two
main methods we have used are chemical bath deposition (CBD) and electrochemical deposition. Over the past few years, most of our work has
been on CBD. CBD refers to film formation from a solution (almost always aqueous) where a chemical reaction slowly occurs to form the required film.
It is thus very different from some other solution methods, such as spin coating, where the material to be deposited already is present in a liquid in a
colloidal or suspended state. Most of our recent work on CBD has been on ZnO with some also on composites and solid solutions.
We are particularly interested in factors that affect reproducibility in CBD. Several such factors that we have identified are: the beneficial effect of
low levels of certain impurities in the deposition bath; differences in the two sides of glass substrates and the effect of the nature of the vessel in which deposition
is carried out. Since ZnO can be used for nanoporous solar cells, we are particularly interested in factors that control the nature of the deposit, in
particular the morphology, porosity and feature size. In multicomponent CBD, there are many more issues than in simple compound formation: the
interactions between different components; whether the film formed is a composite or solid solution; if a composite, how are the different phases intermixed?


Nanoporous, semiconductor-sensitized solar cells

We are studying two types of nanoporous, semiconductor-sensitized cells: all-solid state cells (commonly known as Extremely Thin Absorber
(ETA) cells) and liquid junction cells. In both types of cells, the semiconductor absorber is deposited on a porous oxide (usually TiO2 or
ZnO, which removes electrons) and a hole conductor is infiltrated into the porous network to remove holes. The hole conductor is a solid in the ETA
cell (we use CuSCN) and a liquid electrolyte in the liquid junction cell. We use almost exclusively solution methods to deposit the various components in
these cells, in particular, CBD. We use various absorbing semiconductors: CdS, CdSe, Cu2-xS and Sb2S3. We are investigating the various loss pathways
in these multi-interface cells and how to minimize these losses.

Techniques commonly used/skills acquired in the group

Various methods of solution deposition of semiconductor films, with emphasis on chemical bath deposition.
Chemical composition, structural and morphological properties: Various X-ray diffraction methods, electron microscopy (SEM, TEM, electron diffraction, EDS analysis).
Physical properties: Optical transmission/reflectance, optoelectronic methods (photocurrent and surface photovoltage spectroscopies,
photocurrent-voltage measurements). X-ray photoelectron spectroscopy (chemical analyses and energy level determination).
Most of these instruments are used by the group members themselves.