Page 216 - Organic Electronics in Sensors and Biotechnology

CHAPTER 6

An Introduction

to Organic

Photodetectors

Jingsong Huang
Molecular Vision Ltd.
BioIncubator Unit, London, UK
John deMello
Chemistry Department
Imperial College London, London, UK

6.1 Introduction
In this chapter, we review the use of organic photodiodes (OPDs) as sen-
sitive photodetectors, and we compare their performance characteristics
with conventional vacuum tube and solid-state detectors. Huge research
efforts have been invested in organic light-emitting diodes, solar cells,
and transistors, but organic photodetectors have received far less atten-
tion to date. Although they are structurally similar to organic solar cells,
their performance criteria are quite different. Materials systems and
device geometries that work well for solar energy applications may per-
form poorly when applied to photodetectors, yielding poor spectral
characteristics, excessive noise, or sluggish response. Organic photode-
tectors should not therefore be viewed as a simple offshoot of existing
solar cell research, but as technological devices in their own right with
their own unique set of technical challenges. This chapter is written with
this viewpoint in mind, and offers a tutorial-style introduction to organic
photodetectors that is intended to provide an accessible starting point
for the would-be OPD researcher. We review the fabrication and
operating principles of OPDs and the preferred techniques for reading
them electronically. We introduce the principal figures of merit for
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