Single crystalline pentacene solar cells

Pentacene single crystals were grown from the vapor phase and doped with iodine. Schottky-type solar cells were prepared based on these p-type crystals using rf-magnetron sputtered n-type ITO-window layers and Al or Mg back contacts, respectively. The improvement of the photovoltaic properties due to iodine doping is related to (1) a higher conductivity resulting in a lower series resistance of the devices, (2) a shift of the absorption edge leading to a better match to the solar spectrum, and (3) an increased internal quantum efficiency. The devices were analyzed by measurements of the quantum efficiency, current–voltage curves, and capacitance–voltage characteristics. The solar cells exhibit open circuit voltages up to 955 mV, short circuit current densities of 4.5 mA/cm2, and filling factors in the range of 0.45 resulting in a maximum conversion efficiency of 1.9% for a standard solar spectrum (AM1.5, 100 mW/cm2).