Narrowband‐Absorption‐Type Organic Photodetectors for the Far‐Red Range Based on Fullerene‐Free Bulk Heterojunctions

Abstract

chemical tailoring, [12] their facile lowtemperature processing, [13] and their mechanical flexibility, [14] organic semiconductors bear the promise of delivering narrowband photodetection with high performance and in unconventional settings and form factors, [15] e.g., in low-cost, point-of-use devices for wearable optoelectronics, [16,17] the Internet of Things, [18] computer vision, [19] and biomedicine. [20] Among the several organic narrowband photodetection strategies that have been investigated to date, the so-called narrowband absorption (NBA) strategy-relying on a photoactive layer predominantly absorbing in the target spectral range-has been prominent. [11,15] Alternative narrowband strategies relying on internal optoelectronic filtering effects (such as charge carrier narrowing [21] and charge-injection narrowing [5,22] ) or on microcavity resonance [23] have also been explored, delivering remarkable performance for applications requiring a particularly narrow spectral response. With respect to the NBA strategy, it builds on the inherent spectral tunability and narrowband absorption of many organic semiconductors. [24][25][26][27][28] In particular, NBA photo detectors are inherently nonfiltered, i.e., they have little/negligible impact on the spectral content of the incident light outside the target spectral range. Consequently, NBA photodetectors can potentially deliver multicolor/multispectral detection in a stacked configuration, [29][30][31] a route that is particularly attractive for high-resolution imaging beyond the capabilities of benchmark technologies. In fact, NBA photodetectors have been particularly successful in delivering narrowband functionality in the blue, green, and red spectral regions, attaining spectral responsivity passbands with typical spectral widths of ≈100-150 nm, and specific detectivity values up to the 10 13 Jones range. [11] Developing and emerging applications (e.g., requiring multispectral capability) motivate the effort to expand the scope of organic NBA narrowband photodetectors beyond the boundaries of conventional color detection. In particular, narrowband photodetection in the far-red range (i.e., photodetectors with peak response at 700-750 nm)-dimly visible to the human eye and at the same time distinct from the infrared regionis of considerable interest, in view of its role in many natural Spectrally-selective photodetection via organic semiconductors manifesting narrowband absorption (NBA photodetection) is highly attractive for emerging applications that require ultrathin, lightweight, and low-cost solutions. While successful over mainstream color bands, NBA photodetectors have struggled so far to meet the functional and/or performance demands at longer wavelengths, importantly in the far-red (700-750 nm), a range relevant to diverse applications in analytical biology, medical diagnostics, remote sensing, etc. In consideration of the potential of a nonfullerene-acceptor route to address this challenge, the narrowband photodetection capabilities of SBDTIC, ...

Filter‐Free Band‐Selective Organic Photodetectors

“…The material-dependent conventional PDs usually have a strong spectral crosstalk phenomenon due to a large full width at half maximum (FWHM) of the photodetection bands. [24] The response spectrum with an FWHM of <20 nm was obtained using a microcavity near-infrared (NIR) PD having a highly reflective distributed Bragg reflector (DBR). [18] However, the fabrication of the DBR requires a precise wavelength matching condition and costly process, and the microcavity PDs have limited responsivity and undesired angular dependent photodetection phenomena.…”

Wavelength‐Selective Organic Photodetectors

“…Figure shows D * values extracted from 43 papers reporting narrow‐band OPDs from the year 2012 onwards with an FWHM value of a maximum of 150 nm. [ 4,17–21,25,28,30–34,38–67 ] To get an overview of the current status of the field, it is instructive to plot D * as a function of peak EQE value, J d , and design wavelength. It is important to mention that not in all of these papers the noise currents have been directly measured and D * has often been calculated using , given by Equation (2).…”

“…In literature, there is, however, some inconsistency in the approach to calculate the LDR. In most papers, [ 18,19,28,32,33,42–44,46–48,50,53,55–57,59–61 ] the authors convert the ratio between the maximum and minimum intensity over which the OPD behaves linearly to dB by taking the log (base 10) and multiplying it by a factor 20, while a few authors multiply by a factor 10. [ 33,42 ] This should be taken into account when comparing LDR values.…”

“…The benzodithiophene‐based SBDTIC electron acceptor was utilized in a far‐red OPD. [ 53 ] A rather broad response (FWHM = 141 nm) was achieved in combination with the transparent poly‐TPD donor polymer ( D * = 1.42 × 10 13 Jones). A highly transparent NIR OPD based on an ionic cyanine dye was reported by Zhang et al [ 54 ] Using a rather complex device stack, wherein a thin layer of Cy7‐T was applied in a planar heterojunction (PHJ) with photopolymerized C 60 , a detectivity of 1–3 × 10 12 Jones was obtained (FWHM = 133–141 nm).…”

Bromine Doping of MAPbI3 Films Deposited via Chemical Vapor Deposition Enables Efficient and Photo‐Stable Self‐Powered Photodetectors

“…[ 3–6 ] Interest in self‐powered photodetectors has recently surged due to prospects for the commercialization of portable and wearable applications that can operate without power consumption. [ 6–8 ] However, the key figures of merit of self‐powered perovskite photodetectors still lag far behind their commercial counterparts. [ 9–14 ] The realization of self‐powered perovskite photodetectors for smart sensor systems is highly desirable, but great challenges must first be overcome.…”