Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

Abstract

Spectrally selective light detection is vital for full-colour and near-infrared (NIR) imaging and machine vision. This is not possible with traditional broadband-absorbing inorganic semiconductors without input filtering, and is yet to be achieved for narrowband absorbing organic semiconductors. We demonstrate the first sub-100 nm full-width-at-half-maximum visible-blind red and NIR photodetectors with state-of-the-art performance across critical response metrics. These devices are based on organic photodiodes with optically thick junctions. Paradoxically, we use broadband-absorbing organic semiconductors and utilize the electro-optical properties of the junction to create the narrowest NIR-band photoresponses yet demonstrated. In this context, these photodiodes outperform the encumbent technology (input filtered inorganic semiconductor diodes) and emerging technologies such as narrow absorber organic semiconductors or quantum nanocrystals. The design concept allows for response tuning and is generic for other spectral windows. Furthermore, it is materialagnostic and applicable to other disordered and polycrystalline semiconductors.

Solution-processed semiconductors for next-generation photodetectors

“…To this end, narrowband absorbing organic semiconductors have been explored which can potentially satisfy narrowband responses required for machine vision. 5 However, these devices often use a blend of donor and acceptor (predominantly fullerenes) -both contributing in photocurrent generation and need to be optimized in terms of the spectral shape of light absorption. This has been done for the donor part 6,107 but yet to achieve for the acceptor.…”

“…5,108 Broadband absorbing polymer:fullerene systems have been employed in optically thick junctions (1.5-3 µm) and delivered narrowband spectral responses in red and near-IR with FWHM < 100 nm, D* exceeding 10 12 Jones and 3dB frequency bandwidth of 100's of kHz. 5 This mechanism has been termed charge collection narrowing (CCN) in which only those charges generated in the volume of the active layer are collected. The idea is based on the fact that the electro-optics of thick junctions (d > µm) is substantially different to that of thin photodiodes (d ~ 100's nm).…”

“…5 Its usage has been now expanded to metal halide perovskite films, single crystals and quantum dots. 73,111,112 Lin et al 73 have realized redgreen-blue narrowband photodiodes by introducing ionic dyes in lead iodide and lead perovskites with different halide ratios.…”

“…3 Organic semiconductors are arguably the most optoelectronically adaptable of these classes of materials by virtue of their almost limitless molecular diversity. In particular, they have been shown significant potential for achieving color discrimination through molecular 4 and device architecture 5 tuning, or utilization of both strategies in combination. 6 Low noise, broadband visible-near IR light detection have also been reported.…”

On the unipolarity of charge transport in methanofullerene diodes

“…Irrespective of the nomenclature, fullerenes possess high electron affinities~3.7-4.2 eV in relation to many other organic semiconductors, and hence are considered strong electron acceptors in a variety of applications. Thus elucidating the charge mobility characteristics in fullerene containing films is important given their common usage as electron acceptors in organic solar cells (OSCs), electron transport interlayers in high efficiency organohalide perovskite solar cells, 2 and as a hole blocking layer in ultra-low noise organic 10 and organohalide perovskite photodiodes. 11 In this article we present measurements that allow independent determination of electron and hole mobilities in neat PCBM diode structures, under what may be considered operational conditions for solar cells and photodiodes.…”