Date of this Version
APPLIED PHYSICS LETTERS 91, 203505 (2007)
In this manuscript, the origin of the photomultiplication effect was studied in C60 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 material structures into one organic solar cell device with a configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/pentacene/C60 fullerene/bathocuproine (BCP)/Al. Our results show that both the disordered structure of C60 and the charge trapping effect at the C60 /PEDOT:PSS interface contribute to the photomultiplication effect. By studying the C60-only single layer device, the charge trapping sites are identified to be at the C60 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 C60 disordered structure is much less significant than that by charge trapping at the interface.