Microscopic description of the current–voltage characteristics of a bulk-heterojunction organic solar cell under illumination

Measurement of the local current-voltage (J-V) characteristics of a MDMO-PPV:PCBM bulk-heterojunction (BHJ) solar cell by using light-modulated scanning tunneling spectroscopy (LM-STS) revealed that the open-circuit voltage (V-OC) differs from one region to another. Consequently, when the bias voltage is set near V-OC, the generated photocurrent in some regions is internally lost in other regions through leakage. In the same manner, the external J-V characteristics of a BHJ solar cell device results from numerous parallelly connected local solar cells. LM-STS allows us to interpret the external J-V characteristics of a device in terms of the characteristics of the local solar cells. (C) 2014 The Japan Society of Applied Physics