Photoelectric signals of chlorophyll a Langmuir-Blodgett films

Photoelectric cells of ITO/insulator/chlorophyll a/insulator/InGa liquid metal, containing 1, 2, 4 or 10 LB monolayers of chlorophyll a as photoactive layers and 9–10 stearyl amine films as insulator layers have been studied by measuring the transient photovoltage and transient photocurrent responses in the micro- to millisecond and second time domains, respectively. The signals were created either by a laser pulse or by step-wise excitation. The cells exhibited light-induced charge transport inside the chlorophyll layers in the direction from the InGa to the ITO electrode. The charge movement is explained by an internal electric field due to the metal surface potentials, and was confirmed by measurements for when an external voltage was applied. A model based on a single-step light-induced charge shift is discussed, and the quantum yield for the light-induced charge generation has been estimated to be close to unity.