Abstract
Organic photodiodes (OPDs) are attractive as solution-processed devices for sensing applications. Industrial and medical sensors often have the requirement to operate in the near-infrared (NIR) spectrum between 650 and 900 nm and are ideally visible-blind. Due to the tailored spectral sensitivity of the organic semiconductors, OPDs are attractive as filter-free solid-state alternative. In addition, the large active areas of the OPDs potentially allow fabricating lens-free light-barrier and reflective sensors. In this paper, we discuss different approaches toward NIR sensitive OPDs with a large active area up to 1 cm applying polymers and small molecules as light absorbers. We demonstrate that with layer stacks optimized to the solution-processed semiconductor properties photodiodes with bulk heterojunctions with a minimum external quantum efficiency peak >40% in the NIR and a rectification ratio of ~10 can be achieved, which match industrial sensing requirements. © 2013 IEEE.