Performance of organic photovoltaic devices in the presence of buffer layers

We have investigated the dependence of the efficiency improvement of organic photovoltaic devices on the buffer layer. A device with a three-layer structure of ITO/CuPc/C 60 /BCP/Al was made as a reference through a thermal evaporation method. Characteristic parameters of the photovoltaic devices were measured and analyzed. The obtained open-circuit voltage V OC , short-circuit current density J SC , fill factor (FF), and energy-conversion efficiency (ECE) for the reference device were 0.25 V, 1.05 mA/cm 2 , 0.45, and 0.12%, respectively. Also, devices with five-layer structures of ITO/PEDOT:PSS/CuPc/C 60 /BCP/(LiF or Cs 2 CO 3 )/Al were fabricated, and their electrical characteristics were measured. The V OC , J SC , FF, and ECE for the device with the LiF buffer layer were 0.47 V, 3.31 mA/cm 2 , 0.51, and 0.81%, and those obtained for the device with the Cs 2 CO 3 buffer layer were 0.49 V, 3.52 mA/cm 2 , 0.53, and 0.92%, respectively. The photovoltaic performance of the device with the Cs 2 CO 3 layer was found to be better than those of the others. The V OC , J SC , FF, and ECE for the device with the Cs 2 CO 3 layer were higher than those of the reference device by factors of 1.88, 3.35, 1.18, and 7.67, respectively.