An energy conversion device comprises at least two thin film photovoltaic cells fabricated separately and joined by wafer bonding. This nonwoven composite structure may be used as a wiper or an absorbent material. The resultant intermediate signal is then mixed with another demodulating signal, tunable in relatively smaller frequency steps in order to select the channel containing the radio frequency signal. Then, a post-nitridation process is performed on the high-k dielectric layer after the nitridation process is performed.