iCVD Polymerization: A Novel Technique in Solar Cell Fabrication
Siamak Nejati
In order to create more robust solar cells for the future, one potential pathway is to
integrate polymers into these devices. However, solar cells typically involve nanoscale structures
and materials. The challenge is to enable effective integration of polymers into nanoscale
architectures using suitable processing methodologies. Thus, initiated chemical vapor deposition
(iCVD) polymerization is proposed as a viable means for achieving such integration, for example
in dye-sensitized solar cells (DSSC). Current DSSC technology yields conversion efficiencies of
over 11%, but the use of a liquid electrolyte presents device challenges such as leakage and
corrosion. Using solid and quasi solid-state materials as a substitute for the liquid electrolyte
however present other challenges, particularly with filling the mesopores of the dye sensitized
photoanode when using liquid-based processing. We have therefore utilized iCVD as a viable
liquid-free process for integrating polymer electrolytes like poly (2-hydroxyethyl methacrylate)
(PHEMA) into the mesoporous electrode. Cross-sectional SEM showed complete pore filling of
the electrode up to 12 µm thick. Solar illumination under different light intensities showed the
open circuit voltage of the cell is significantly higher than that of the corresponding liquid
electrolyte cell. Electrochemical impedance spectroscopy revealed that the electron
recombination time constant of the cell fabricated with iCVD polymer is higher. With iCVD, we
expect to be able to overcome liquid based processing difficulties, and find synthesis routes and
materials suitable for other solar cell devices as well.