Design and characterization of polymer-fullerene bulk heterojunction solar cells

Design and characterization of polymer-fullerene bulk heterojunction solar cells were experimentally studied in this study. In the experiments, ITO or highly conductive PEDOT:PSS coated glasses were used as anode, P3HT and [60]PCBM or [70]PCBM were used as active layer materials and conductive PEDOT:PSS used as hole conducting layer. Aluminum, Woods metal and Ga-In eutectic were tested as cathode in the devices. All the experiments were done under atmospheric conditions. Conductive and highly conductive PEDOT:PSS, and blend of P3HT:PCBM materials were applied by spin coater. Al deposition was done by thermal evaporator. On the other hand, Ga-In eutectic was directly applied over the active layer while Woods metal was deposited after melting. Electrical characterizations of devices are done by Keithley 2400 and 2612A source meter and 100 W halogen lamp. Light intensity of halogen lamp was measured by MP-100 Apogee Instruments Pyranomoter and set to 1000 W/m2. In Al cathode structure, two working devices with appropriate diode characteristics were recorded. This was the same for Ga-In eutectic devices while no devices with Woods metal cathode structure were successfully performed. The best working device, which is one of with Ga-In eutectic cathode, showed the electrical characteristics of 0.14 % power conversion efficiency, 470 mV open circuit voltage, 1.09 mA/cm2 short circuit current density and 27 % fill factor over 0.03 cm2 active area; these values are not as good as the values reported in the literature, probably because of the high degradation with oxygen under atmospheric conditions. In addition to this, the difficulties encountered during Al coating further decreased the efficiency of devices containing this metal.