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. 2023 Jun 9;9(23):eadh2694.
doi: 10.1126/sciadv.adh2694. Epub 2023 Jun 7.

Enhanced sub-1 eV detection in organic photodetectors through tuning polymer energetics and microstructure

Polina Jacoutot  1 , Alberto D Scaccabarozzi  2 , Davide Nodari  1 , Julianna Panidi  1 , Zhuoran Qiao  1 , Andriana Schiza  3 , Alkmini D Nega  4 , Antonia Dimitrakopoulou-Strauss  4 , Vasilis G Gregoriou  3   5 , Martin Heeney  1   6 , Christos L Chochos  3   5 , Artem A Bakulin  1 , Nicola Gasparini  1
Affiliations

Enhanced sub-1 eV detection in organic photodetectors through tuning polymer energetics and microstructure

Polina Jacoutot et al. Sci Adv. .

Abstract

One of the key challenges facing organic photodiodes (OPDs) is increasing the detection into the infrared region. Organic semiconductor polymers provide a platform for tuning the bandgap and optoelectronic response to go beyond the traditional 1000-nanometer benchmark. In this work, we present a near-infrared (NIR) polymer with absorption up to 1500 nanometers. The polymer-based OPD delivers a high specific detectivity D* of 1.03 × 1010 Jones (-2 volts) at 1200 nanometers and a dark current Jd of just 2.3 × 10-6 ampere per square centimeter at -2 volts. We demonstrate a strong improvement of all OPD metrics in the NIR region compared to previously reported NIR OPD due to the enhanced crystallinity and optimized energy alignment, which leads to reduced charge recombination. The high D* value in the 1100-to-1300-nanometer region is particularly promising for biosensing applications. We demonstrate the OPD as a pulse oximeter under NIR illumination, delivering heart rate and blood oxygen saturation readings in real time without signal amplification.

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Figures

Fig. 1.
Fig. 1.. TQ-3T polymer structure and OPD materials characterization.
(A) Chemical structure of low bandgap conjugated polymers TQ-T and TQ-3T. (B) Normalized visible-IR absorption spectra of conjugated donor polymers and non-fullerene acceptor IEICO-4F. (C) Energy diagram of the materials used in OPD measured by air photoelectron spectroscopy (APS), with workfunction values of 4.7 and 4.6 eV for TQ-3T and TQ-T, respectively, obtained by Kelvin probe measurements. 2D GIWAXS maps of (D) TQ-3T and (E) TQ-3T:IEICO-4F; (F) in-plane and out-of-plane profiles of pristine films and the D:A blend. a.u., arbitrary units.
Fig. 2.
Fig. 2.. OPD architecture and performance.
(A) Inverted OPD device structure of the TQ-3T–based device. (B) Current-voltage characteristics of TQ-3T:IEICO-4F OPDs under light and dark conditions. (C) Responsivity and specific detectivity at −2 V applied bias.
Fig. 3.
Fig. 3.. OPD response speed and dynamic range.
Dynamic measurements with TQ-3T:IEICO-4F all performed at 940-nm illumination and −2 V applied bias. (A) Cut-off frequency at −3 dB. (B) Transient photocurrent measurements with rise and fall times. (C) LDR measurements and extrapolation of the LDR into the noise floor, with calculation of the NEP.
Fig. 4.
Fig. 4.. TAS analysis of the OPD blend.
(A) Broadband visible-IR transient absorption spectra of TQ-3T:IEICO-4F blend upon 1300-nm pump excitation. Decomposed spectra (B) and kinetics (C) of the two-component GA depicting decaying excitonic and growing charge dynamic. mOD, mean optical density; OD, optical density.
Fig. 5.
Fig. 5.. Finger PPG testing under NIR illumination.
(A) Transmittance PPG collected from a volunteer’s finger under different NIR illumination wavelengths. (B) Comparison of PPG waveform and its derivatives, including the second derivative APG, highlighting the key areas of interest in a cardiac cycle.
See this image and copyright information in PMC

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