Organic Photodetectors with Gain and Broadband/Narrowband Response under Top/Bottom Illumination Conditions

Abstract

Organic photodetectors (OPDs) possessing broadband/narrowband photodetection capability and gain have great potential in integrated optoelectronics products. In this work, OPDs with a device structure of ITO/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/thick active layer/semitransparent Al electrode exhibit the extraordinary functions, gain and bidirectional photodetection capability with tunable spectral response range. For the binary OPDs with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) (100:1, wt/wt) as active layer, the OPDs exhibit narrowband response from 620 to 700 nm with full‐width at half maximum (FWHM) of ≈30 nm under bottom illumination condition and broadband response from 300 to 700 nm under top illumination condition, respectively. To further confirm and optimize the extraordinary functions of OPDs, ternary devices are fabricated with P3HT:poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dit‐hiophene‐co‐3‐fluor‐othieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th):PC71BM (50:50:1, wt/wt) as active layer. The narrowband response can be adjusted to near infrared (NIR) region from 760 to 860 nm. The broadband response can be extended to NIR region with response range from 300 to 860 nm. Meanwhile, external quantum efficiency (EQE) spectral shape of the ternary OPDs becomes flatter under top illumination condition and can be kept constant under different bias. The ternary OPDs exhibit similar EQE values of ≈2000% and specific detectivity larger than 1011 Jones at −50 V bias under bottom and top illumination conditions.

Recent Progress on Photomultiplication Type Organic Photodetectors

“…Recently, Zhang et al. reported the PM type OPDs based on thick active layer and semitransparent Al electrode, exhibiting broadband or narrowband response spectra under light illumination from top Al or bottom ITO sides, respectively …”

Efficiency and spectral performance of narrowband organic and perovskite photodetectors: a cross-sectional review

“…This typically relies on the incorporation of trap states for one particular type of carrier (referred to as the minority carrier in this context). For example, Miao et al and Wang et al relied on minute amounts of fullerenes to introduce a trap state within a holeconducting polymer (P3HT) [30][31][32], while Shen et al employed inorganic quantum dots to achieve a similar effect within an organic donor-acceptor blend [33,34]. Under illumination and sufficiently strong bias, the injection barrier for majority carriers (i.e., the more mobile carrier in the photoactive material) may be thinned to the point at which majority carrier tunnelling into the photoactive material occurs [29].…”

“…In either case, they have been utilised as donors (within donor-acceptor BHJs or PHJs) or as hole transporting semiconductors (if used in single-component form). Depending on the composition, their absorption onset can fall in different spectral regions-for instance, in the blue (as in some polyfluorene-based polymers) [49-51, 84, 86, 89-95], in the red (as in some polythiophenes) [25, 30-33, 42, 80-82, 84, 96, 97], and in the far red/NIR (as in a number of so-called D-A polymers) [25,32,42,[98][99][100].…”

“…Finally, if minute amounts of minority carrier traps are incorporated into the single-component (either per se or de facto) photoactive layer, IntF-1 may take place with a concurrent gain mechanism (IntF-1x in short form) (cf. section 3.2) [25,[30][31][32]. The latter case is often referred to as charge injection narrowing in the literature [29].…”

“…EQE values (in primary photocurrent mode) in the 50%-80% range have been achieved throughout the visible range [11, 22, 46, 57-59, 61, 69-72, 95, 120, 121, 128, 129], with associated spectral widths of around 90-150 nm. Operation in secondary photocurrent mode has also delivered large EQE values [27,[30][31][32]131], typically in the 10 3 %-10 4 % range, and up to ≈2·10 5 in one instance [131]. Ultranarrowband photodetectors (FWHM EQE <50 nm) have also been obtained in a conspicuous number of works [25, 30-32, 42, 54, 65, 73, 75, 76, 80-82, 86, 136-139].…”