High performance transparent conducting materials for solar cells

Atomic layer deposition (ALD) has been widely used for the development of
buffer layers on copper-indium-gallium-sulfide and copper-indium-galliumselenide
solar cells with appropriate electronic properties; however, still an
in-depth understanding of the growth properties of the ternary oxide and
their related properties is lacking. In this thesis, we investigate the interface
chemistry and mixing of binary ALD processes on the growth and resulting
optoelectronic properties by altering the supercycle process parameters (pulse
ratio and bilayer period) of the ternary ALD process for zinc magnesium
oxide(ZMO) and zinc tin oxide (ZTO). We show that the interplay between
ZnO and MgO interfaces in the synthesis of ZMO leads to enhanced growth
of the MgO layer by the ZnO surface. Similarly, we validate the inhibited
growth of ZnO by SnOx surface in ALD deposited ZTO films. We propose
probing the effect of the bilayer period in growth of ternary oxides by ALD
can serve as an effective alternative to QCM in understanding the growth
kinetics which can be extended to many other materials.
We show that the optical properties of the ternary films not only depend on
the composition but also depend on the bilayer period at a given composition.
More specifically, the bandgap at a given composition for both ZMO
and ZTO films is high at the smallest bilayer period and starts decreasing
with increase in bilayer period, reaching the bandgap value of ZnO for bilayer
periods greater than 40. We explore the possible mechanisms for the change
in optical properties with bilayer period. We propose bilayer period as an
effective parameter alongside composition to tune the bandgap and demonstrate
the application of which by depositing ALD grown ZMO buffer layers
for chalcopyrite solar cells.