Optical interference effect in layered organic materials studied by UV-Vis absorption spectroscopy

In this report, UV-Vis absorption spectra of CaF2⧹Alq3, CaF2⧹C60 and CaF2⧹C60⧹Alq3 versus thickness of the organic layers are compared with the calculated spectra from transfer matrix calculation. Contrary to the total difference between the experimental results and the exponential decay calculation, the qualitative and quantitative similarity between the transfer matrix calculation and experimental results indicates that optical intensity in these organic films can be modulated by their thicknesses, and transfer matrix method is demonstrated as a useful tool to calculate the light propagation in thin-layered organic films. Further calculation shows that the optical electric field near the CuPc⧹C60 interface can be easily modulated by varying the thickness of C60 if the reflection of cathode is taken into account. Our optimization thickness of solar cells with structure of ITO⧹CuPc⧹C60⧹buffer⧹Al is 15 nm for CuPc and 52 nm for C60 when the buffer is chosen as 6 nm Alq3.