  Supercapacitors, S-C - capacitors that take advantage of the large
capacitance at the interface between an electrode and an electrolyte - have
found many short-term energy applications. We concentrate here on optically
induced, electrical and thermal effects. The parallel plate cells were made of
two transparent electrodes (ITO), each covered with semiconductor-embedded,
active carbon (A-C) layer. While A-C appears black, it is not an ideal
blackbody absorber that absorbs all spectral light indiscriminately. In
addition to relatively flat optical absorption background, A-C exhibits two
distinct absorption bands: in the near-IR and in the blue. The first may be
attributed to absorption by OH- group and the latter, by scattering, possibly
by surface plasmons. Here, optical and thermal effects of sub-micron size SiC
particles that are embedded in A-C electrode, are presented. Similarly to
nano-Si particles, SiC exhibits blue band absorption, but it is less likely to
oxidize. Using Charge-Discharge (CD) experiments, the relative optically
related capacitance increase may be as large as ~34% (68% when the illuminated
area is taken into account). Capacitance increase was noted as the illuminated
samples became hotter. This thermal effect amounts to 20% of the overall
relative change using CD experiments. The thermal effect was quite large when
the SiC particles were replaced by CdSe/ZnS quatum dots; for the latter, the
thermal effect was 35% compared with 10% for the optical effect. When analyzing
the optical effect one may consider two processes: ionization of the
semiconductor particles and charge displacement under the cell's terminals - a
dipole effect. Our model suggests that the capacitance increase is related to
an optically induced dipole.
