Photovoltaic properties and stability of pentacene-fullerene double heterojunction devices

The photovoltaic properties of thirty two pentacene (P5) / fullerene (C₆₀) / barthocuproine (BCP) double heterojunction organic photovoltaic devices have been studied as a function of P5 (donor) thickness from 20-76 nm. Both the short circuit current density and power conversion efficiency initially increase with thickness and then decrease for thickness greater than 60 nm. The open circuit voltage and device fill factor showed less variation with P5 thickness. Device characteristics of all devices showed degradation after storage for 20 hours in nitrogen and in darkness. The degradation could not be reversed by thermal annealing in nitrogen and is attributed to exposure to air during initial electrical measurements.