A reduction of material consumption in thin-film photovoltaic devices can make solar energy economically more viable.
However, since thin films essentially absorb less light, there is an imminent need for existing technology to improve light harvesting. We present an effective approach of better light absorption, enhanced photocurrent generation and therefore higher quantum efficiency of poly (3-hexylthiophene): 1-(3-methoxycarbonyl) propyl-1-phenyl-[6, 6]-methanofullerene (P3HT:PCBM) bulk heterojunction photovoltaic/photodetector devices. We have integrated a thin semi-continuous gold film (SCGF) (~20nm) sputtered at percolation threshold between the active P3HT:PCBM layer and the indium-tin-oxide (ITO) electrode. At critical metal concentrations, i.e. percolation threshold, the light reaching the SCGF undergoes a broadband trapping with characteristic time of 200 fs, through complex interactions with fractal gold clusters. This thin SCGF together with the ITO serves as an anode. The interface between SCGF and the polymer represents the metaldielectric composite (MDC) that supports broad-band surface plasmon resonances that store electromagnetic radiation at the nanoscale and acts as an effective bulk type of concentrator without the need of increasing the photovoltaic device physical collection area. Here we report a six-fold enhancement in the integral quantum efficiency over the solar spectrum for device employing plasmon-active gold layer. Such enhancement is an important contribution for the future design of more efficient photodetecting/photovoltaic devices. The experimental results are supported by the theoretical modeling of metal-dielectric composites by block elimination method in 3D. The AC and DC responses of MDC, local field distribution, broad optical response and photon trapping in the percolating MDC were numerically calculated.