Cathode buffer composed of fullerene-ethylenediamine adduct for an organic solar cell

We developed a fullerene-ethylenediamine adduct (C₆₀P-DC) for a cathode buffer material in organic bulk heterojunction solar cells, which enhance the open-circuit voltage (V_oc). The evaporative spray deposition using ultra dilute solution (ESDUS) technique was employed to deposit the buffer layer onto the organic active layer to avoid damage during the deposition. By the insertion of a C₆₀P-DC buffer layer, V_oc and power conversion efficiency (PCE) were increased from 0.41 to 0.57 V and from 1.65 to 2.10%, respectively. The electron-only device with the C₆₀P-DC buffer showed a much lower current level than that without the buffer, indicating that the V_oc increase is caused not by vacuum level shift but by hole blocking. The curve fitting of current density-voltage (J-V) characteristics to the equivalent circuit with a single diode indicated that the decrease in reversed saturation current by hole blocking increased caused the V_oc.