Plasmon enhancement of organic photovoltaic efficiency in tandem cells of pentacene/C60

The effects of thin silver films embedded in a tandem pentacene/C-60 photovoltaic cell are investigated. A 2 nm Ag film improves the device's power efficiency under white light illumination from 0.32% to 1.11% by almost doubling its open circuit voltage and enhancing its short circuit current density. The doubled open circuit voltage is due to the formation of two separated photovoltaic pentacene/C-60 cells in series where discontinuous silver clusters provide carrier recombination centers. The increased photocurrent density is partly ascribed to improved charge separation and transport associated with the silver layer. In addition, wavelength dependent measurements suggest that plasmon-enhanced light absorption by pentacene due to surface plasmon resonance of silver nanoparticles contributes as much as a factor of 4 to the power efficiency near the plasmon resonance around 450 nm.