Measurement of exciton diffusion lengths in optically thin organic films

Abstract

Spectrally resolved photoluminescence quenching (SR-PLQ) is a convenient and accurate method for measuring the exciton diffusion length of organic materials; however, the requirement of optically thick films demanded by this technique poses practical limitations to its implementation. Through simulations of the optical field and exciton dynamics, we extend SR-PLQ to the case of optically thin organic films; i.e., films whose thickness is comparable to or less than that of the optical absorption length across the entire optical absorption spectrum. This allows for the characterization of films whose thickness is comparable to that used in practical organic optoelectronic devices. Using this method, we measure the diffusion lengths of several squaraine donors, the acceptor 3,4,9,10 perylenetetracarboxylic dianhydride, and the relationship between the donor, boron subphthalocyanine thickness and diffusion length.