Intrinsic Detectivity Limits of Organic Near‐Infrared Photodetectors

Gielen, Sam; Kaiser, Christina; Verstraeten, Frederik; Kublitski, Jonas; Benduhn, Johannes; Spoltore, Donato; Verstappen, Pieter; Maes, Wouter; Meredith, Paul; Armin, Ardalan; Vandewal, Koen

doi:10.1002/adma.202003818

Cited by 116 publications

(194 citation statements)

References 51 publications

(75 reference statements)

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“…This problem can be circumvented by using narrow-gap polymer donors such as PBTQ(OD) or PTTBAI, which show strongly redshifted EQE spectra when blended with PC70BM as previously reported. 27 As shown in Figure 2c, U app is around 22 meV in this case. While deviations of the type U app > + 10 meV are due to the presence of other absorbing species like CT states or deep trap states, small deviations of U app around are likely caused by interference effects, i.e.…”

Section: Figure 1 | Eqe Andsupporting

confidence: 53%

A Universal Urbach Rule for Disordered Organic Semiconductors

Kaiser

Sandberg

Zarrabi

et al. 2021

Preprint

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In crystalline semiconductors, the sharpness of the absorption spectrum onset is characterized by temperature-dependent Urbach energies. These energies quantify the static, structural disorder causing localized exponential tail states, and the dynamic disorder due to electron-phonon scattering. The applicability of this exponential-tail model to molecular and amorphous solids has long been debated. Nonetheless, exponential fittings are routinely applied to the analysis of the sub-gap absorption of organic semiconductors alongside Gaussian-like spectral line-shapes predicted by non-adiabatic Marcus theory. Herein, we elucidate the sub-gap spectral line-shapes of organic semiconductors and their blends by temperature-dependent quantum efficiency measurements in photovoltaic structures. We find that the Urbach energy associated with singlet excitons universally equals the thermal energy regardless of static disorder. These observations are consistent with absorption spectra obtained from a convolution of Gaussian density of excitonic states weighted by a Boltzmann factor. A generalized Marcus charge transfer model is presented that explains the absorption spectral line-shape of disordered molecular matrices, and we also provide a simple strategy to determine the excitonic disorder energy. Our findings elaborate the true meaning of the dynamic Urbach energy in molecular solids and deliver a way of relating the photo-physics to static disorder, crucial for optimizing molecular electronic devices such as organic solar cells.

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Section: Figure 1 | Eqe Andsupporting

confidence: 53%

A Universal Urbach Rule for Disordered Organic Semiconductors

Kaiser

Sandberg

Zarrabi

et al. 2021

Preprint

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“…2c , where 30 meV. The problem can be circumvented by using narrow-gap polymer donors such as PBTQ(OD) or PTTBAI, which show strongly redshifted EQE spectra when blended with PC 70 BM as previously reported 35 . As shown in Fig.…”

Section: Resultsmentioning

confidence: 91%

“…Examples for EQE tails partially dominated by b , the neat donor absorption or by c , the neat acceptor absorption hence showing in some parts of the spectrum. EQE spectra of PTTBAI:PC 70 BM and PBTQ(OD):PC 70 BM are taken from reference 35 . …”

Section: Resultsmentioning

confidence: 99%

A universal Urbach rule for disordered organic semiconductors

et al. 2021

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In crystalline semiconductors, absorption onset sharpness is characterized by temperature-dependent Urbach energies. These energies quantify the static, structural disorder causing localized exponential-tail states, and dynamic disorder from electron-phonon scattering. Applicability of this exponential-tail model to disordered solids has been long debated. Nonetheless, exponential fittings are routinely applied to sub-gap absorption analysis of organic semiconductors. Herein, we elucidate the sub-gap spectral line-shapes of organic semiconductors and their blends by temperature-dependent quantum efficiency measurements. We find that sub-gap absorption due to singlet excitons is universally dominated by thermal broadening at low photon energies and the associated Urbach energy equals the thermal energy, regardless of static disorder. This is consistent with absorptions obtained from a convolution of Gaussian density of excitonic states weighted by Boltzmann-like thermally activated optical transitions. A simple model is presented that explains absorption line-shapes of disordered systems, and we also provide a strategy to determine the excitonic disorder energy. Our findings elaborate the meaning of the Urbach energy in molecular solids and relate the photo-physics to static disorder, crucial for optimizing organic solar cells for which we present a revisited radiative open-circuit voltage limit.

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“…─ 0.1 V, is barely influenced by shunt , hence D (─ 0.1 V) ≈ 0 . 13 It was further suggested that for narrow-gap blends, D (─ 0.1 V) decreases exponentially with increasing CT . CT from the blend as the intercept of the measured EQEPV and calculated EQEEL.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, as the bandgap energy decreases, 0 is known to increase relative to shunt . In narrow-gap organic semiconductor blends designed for near-infrared photodetection, it was observed recently that D in reverse bias shows almost ideal diode behaviour, 13 allowing for D to be fitted with eq. 1.…”

Section: Introductionmentioning

confidence: 99%

Mid-gap Trap State Mediated Dark Current in Organic Photodiodes

Kaiser

Sandberg

Zeiske

et al. 2021

Preprint

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Photodiodes are ubiquitous in industry and consumer electronics. New applications for photodiodes are constantly emerging, such as the internet of things and wearable electronics that demand different mechanical and optoelectronic properties from those provided by conventional inorganic devices. This has stimulated considerable interest in the use of next generation semiconductors, particularly the organics, which provide a vast palette of available optoelectronic properties, can be incorporated into flexible form factor geometries, and promise extremely low cost, low embodied energy manufacturing from earth abundant materials. The sensitivity of a photodiode to low light intensities (typically important in these new applications) depends critically on the dark current. Organic photodiodes, however, are characterized by a much higher dark current than expected for thermally excited band-to-band transitions. Here, we show that the lower limit of the dark current is given by recombination via mid-gap trap states. This new insight is generated from temperature dependent dark current measurements of narrow-gap photodiodes for the near-infrared. Based on Shockley-Read-Hall statistics, a diode equation is derived which can be used to determine an upper limit for the specific detectivity and to explain the general trend observed for the light to dark current ratio as a function of the experimental open-circuit voltage for a series of organic photodiodes. A detailed understanding of the origins of noise in any detector is fundamental to defining performance limitations and thus is critical to materials and device selection, design and optimisation for all applications. Our work establishes these important principles for organic semiconductor photodiodes for the near-infrared.

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Intrinsic Detectivity Limits of Organic Near‐Infrared Photodetectors

Abstract: Near-infrared (NIR) light detection is key to an ever-growing demand for technical solutions in applications such as surveillance systems, facial recognition, industrial sorting and inspection, pulse oximetry, optical coherence tomography, and

Cited by 116 publications

References 51 publications

A Universal Urbach Rule for Disordered Organic Semiconductors

A Universal Urbach Rule for Disordered Organic Semiconductors

A universal Urbach rule for disordered organic semiconductors

Mid-gap Trap State Mediated Dark Current in Organic Photodiodes

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