インピーダンス分光法を用いた有機薄膜太陽電池動作中でのドナー・アクセプター界面近傍における内蔵電位のin situ評価

抄録

Open-circuit voltage (V_OC) plays a key role of determining the power conversion efficiency for solar cells, as well as short-circuit current. However, the origins of V_OC have still remained unsolved for organic solar cells. Although V_OC has been reported to depend on the electronic states at the Donor/Acceptor (D/A) interface such as the energy difference (ΔE_HL) between HOMO (the highest occupied molecular orbital) of donor and LUMO (the lowest unoccupied molecular orbital) of acceptor, some organic solar cells did not exhibit such the dependence. This is because previous discussion has been based on the D/A interfacial electronic states under “dark condition”. Recently, we have performed in situ impedance spectroscopy to examine the correlation between V_OC and the electronic states (built-in potential: V_bi) in the vicinity of the D/A interface upon photo-irradiation, and found an excellent agreement between V_OC and the sum of V_bi estimated from capacitance-voltage (C-V) characteristics.