Peculiarities of room temperature organic photodetectors.

Organic semiconductors (OSCs) have been considered as projecting family of optoelectronic materials broadly investigated for more than 40 years due to capability to tune properties by adjusting chemical structure and simple processing. The OSCs performance has been substantially increased, due to the fast development in design and synthesis. The spectral response of OSCs was extended from ultraviolet (UV) to near infrared (NIR) wavelength region. There are papers reporting detectivity (D*) higher than the physical limits set by signal fluctuations and background radiation. This paper attempts to explain the organic photodetectors' peculiarities when confronted with typical devices dominating the commercial market. To achieve this goal, the paper first briefly describes OSC deposition techniques, diametrically opposed to those used for standard semiconductors. This was followed by a more detailed discussion of basic physical properties, contributing to the photodetectors' performance including absorption coefficient, conduction mechanism, charge generation and charge transport. These effects are very different from those found in inorganic semiconductors (ISCs). The second part of the paper describes the main modes of OSC based photodetectors [photoconductors, photodiodes and field effect transistor photodetectors (FET)] with emphasis on their special features that distinguish them from standard photodetectors. Final part of the paper shows current state-of-the-art of various types/structures of photodetectors and routes for further improvement. The upper detection limit for OSC photodiodes has been shown to be comparable to that for ISC photodiodes with nearly three orders of magnitude variation. The D* overestimates (especially organic based FET phototransistors) were explained.