Origin of photomultiplication in C60 based devices

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Abstract
In this manuscript, the origin of the photomultiplication effect was studied in C 60 based devices by evaluating the wavelength dependent external and internal quantum efficiencies under various biases. The effect of materials with disordered structures on the photomultiplication effect was determined by intentionally integrating both ordered and disordered materialstructures into one organic solar cell device with a configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) ( PEDOT : PSS ) ∕ pentacene ∕ C 60 fullerene/bathocuproine (BCP)/Al. Our results show that both the disordered structure of C 60 and the charge trapping effect at the C 60 ∕ PEDOT : PSS interface contribute to the photomultiplication effect. By studying the C 60 -only single layer device, the charge trapping sites are identified to be at the C 60 and PEDOT:PSS interface. The interfacial traps behave as an electronic valve that enables a significant increase in electron injection, which causes the photomultiplication phenomena. Quantitative comparisons indicate that photomultiplication induced by C 60 disordered structure is much less significant than that by charge trapping at the interface.