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Title: Low-noise Organic Photodiodes with Near-infrared Sensitivity
Committee:
Dr. Bernard Kippelen, ECE, Chair , Advisor
Dr. Douglas Yoder, ECE
Dr. Juan-Pablo Correa-Baena, MSE
Dr. Andrew Peterson, ECE
Dr. Rosario Gerhardt, MSE
Abstract: The objective of this dissertation is to create and develop approaches for the fabrication of organic photodiodes (OPDs) with near-infrared (NIR) response. This is achieved by (i) using organic materials as the absorber or photoactive layer (PAL) that have NIR responsivity; and (ii) implementing two fabrication approaches which reduce the noise of OPDs. The materials used in the absorber or PAL for both fabrication approaches are the polymer PCE10, which acts as an electron donor, and the fullerene PC71BM, which acts as an electron acceptor. The absorber or PAL is sandwiched between two different electrodes with different work function (WF) values, enabling the asymmetry required in the OPDs for the extraction of carriers. In the first approach, the PAL thickness is tuned to reduce the electronic noise. Two specific PAL thicknesses (700 nm and 1150 nm) are studied in depth. OPDs with these thicknesses reach low root-mean-square (RMS) noise current values in the order of tens of fA. However, the sensitivity of the OPDs with PAL thickness of 700 nm is observed to be broadband, in contrast to OPDs with PAL thickness of 1150 nm, whose sensitivity is more narrowband. In the second approach, the thickness of the PAL is reduced to 170 nm. For this thinner layer, it is observed that the RMS noise current values can be in the order hundreds of fA. Then, it is proposed that, for the same PAL thickness, the RMS noise currents can be reduced to tens of fA through a passivation process of the interface between the PAL and the hole-collecting electrode (HCE) based on atomic layer deposition (ALD) using the trimethylaluminum and water precursors. Simulations using an equivalent circuit are presented to understand the different contributions to the electronic noise for both approaches. The noise equivalent power (NEP) and the specific detectivity (D*) are measured and benchmarked to state-of-the-art OPDs finding comparable values (D* = 2 - 3 Tera-Jones). Potential applications of the PCE10:PC71BM OPDs are discussed in the context of biomedical sensors, night vision, and the Internet of things.
