Doctoral Researchers

Supervisors: Karl Leo, Alexander Eychmüller

a) Cavity enhanced narrowband organic photodetectors.[1] b) Tunable absorption and emission of three to six monolayers of CdSe nanoparticles.[4]

Infrared detectors serve many important purposes in areas such as health monitoring, agriculture, food processing, explosive detection etc. Semiconductor nanoparticles (NPs) are very suitable for sensors, in particular for infrared sensors, due to good photoresponse and tunability. Here, we wish to study the device integration of such nanoparticles in cavity-enhanced devices to reach spectroscopic resolution of the photoresponse.

Nowadays, narrowband photodetection is realized by dispersive elements (e.g., grating in a monochromator) in combination with broad band detectors such as Si or InGaAs. Recently, novel narrowband organic detectors using cavity-enhanced charge-transfer state absorption have been realized [1] This new concept allows for a monolithic integration of several detectors into a miniaturized spectrometer. However, for wavelengths beyond 1600 nm, organic absorbers are less suited [2,3].

The aim of this project is to employ semiconductor NPs like PbS and PbSe in cavity-enhanced photodetectors to reach narrowband detection beyond 2000 nm. We will prepare novel NP solutions and characterize their properties. NPs from this material class are chemically stable in air, photo-stable and have a broad tunability of the absorption in the infrared wavelength range [4]. First, we will produce photoconductive lateral devices to investigate the charge carrier transport properties and optimize the processing conditions. In a second step, we will investigate photodiodes by combining the NPs with organic materials. For this purpose, we plan to use ligand-exchanged NPs allowing to use water-based solutions, compatible with organic underlayers, for the processing. The other layers of the devices are going to be processed by thermal evaporation in vacuum. The compatibility of typical small molecule organic semiconductors with aqueous conditions is shown in ref. [5,6]. The NPs will be integrated in organic p-i-n photodiodes without and with additional optical cavities. The latter approach will enable wavelength-selective detection of photons in the infrared, beyond nowadays detection range, which can be tuned by the resonance of the optical cavity. Such hybrid (NP-organic) photodetectors will be easy processable and cheap and can be hopefully integrated in to miniaturized spectrometers which are suitable for mobile material sensing [7].

Literature:

[1] Bernhard, S.; Mischok, A.; Benduhn, J.; Zeika, O.; Ullbrich, S.; Nehm, F.; Böhm, M.; Spoltore, D.; Fröb, H.; Körner, C.; Leo, K.; Vandewal, K., Organic narrowband near-infrared photodetectors based on intermolecular charge-transfer absorption. Nature Communications 2017, 8, 15421.

[2] Benduhn, J.; Tvingstedt, K.; Piersimoni, F.; Ullbrich, S.; Fan, Y.; Tropiano, M.; McGarry, K. A.; Zeika, O.; Riede, M. K.; Douglas, C. J.; Barlow, S.; Marder, S. R.; Neher, D.; Spoltore, D.; Vandewal, K., Intrinsic non-radiative voltage losses in fullerene-based organic solar cells. Nature Energy 2017, 2, 17053.

[3] Gielen, S.; Kaiser, C.; Verstraeten, F.; Kublitski, J.; Benduhn, J.; Spoltore, D.; Verstappen, P.; Maes, W.; Meredith, P.; Armin, A.; Vandewal, K. Intrinsic Detectivity Limits of Organic Near‐Infrared Photodetectors. Advanced Materials 2020, 32 (47), 2003818

[4] Galle, T.; Samadi Khoshkhoo, M.; Martin-Garcia, B.; Meerbach, C.; Sayevich, V.; Koitzsch, A.; Lesnyak, V.; Eychmüller, A., Colloidal PbSe Nanoplatelets of Varied Thickness with Tunable Optical Properties. Chemical Materials 2019, 31, 3803.

[5] Someya, T.; Dodabalapur, A.; Gelperin, A.; Katz, H.E.; Zhenan Bao, Integration and Response of Organic Electronics with Aqueous Microfluidics. Langmuir 2002, 18 (13), 5299–5302

[6] Rahmanudin, A.; Marcial-Hernandez, R.; Zamhuri, A.; Walton, A.S.; Tate, D.J.; Khan, R.U.; Aphichatpanichakul, S.; Foster, A.B.; Broll, S.; Turner, M.L. Organic Semiconductors Processed from Synthesis-to-Device in Water. Advanced Science 2020, 7 (21), 2002010

[7] Tang, Z.; Ma, Z.; Sánchez‐Díaz, A.; Ullbrich, S.; Liu, Y.; Siegmund, B.; Mischok, A.; Leo, K.; Campoy‐Quiles, M.; Li, W.; Vandewal, K. Polymer: fullerene bimolecular crystals for near‐infrared spectroscopic photodetectors. Advanced Materials 2017, 29 (33), 1702184