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OrganicElectronics

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Administrator: Francesco
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Created 8 Apr 2018
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4 Articles

My contribution to the Organic Electronic literature.

Enhancing Efficiency of Organic Bulkheterojunction Solar Cells by Using 1,8-Diiodooctane as Processing Additive

Organic solar cells (OSCs) are attractive as an al- ternative to inorganic devices for their easy fabrication and solution-processability. A major and unsolved problem with bulk heterojunction devices remains the optimization of the network morphology. Here, we discuss the influence of the 1,8-diiodooctane (DIO) solvent additive on the efficiency of OSCs and show that by selectively controlling the crystallization of the organic ma- terial, the power conversion efficiency (PCE) can be increased by about 30%. For P3HT:PCBM-based devices, the power con- version efficiency (PCE) was increased from 3.7% to 4.9% for PCPDTBT:P3HT:PCBM-based devices from 3.2% to 4.1%. This improvement is due to the higher I/subSCsub/ , which is in agreement with the higher external quantum efficiency (EQE) observed on the de- vices fabricated with DIO. We correlate this to an increase of the surface roughness observed with atomic force microscopy (AFM) analysis. We demonstrate that the effect of the DIO additive is equivalent to a high-temperature thermal annealing.

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Francesco Arca (@Francesco)
Published in 
 · 10 Jun 2018
Fig. 1. P3HT:PCBM (1:0.75 wt.) blend. (a) Energy band diagram (flat band condition). (b) EQE measure
I. INTRODUCTION OVER the past few years, interest in cheap photovoltaic solutions has increased because of growing demand for renewable energy sources. Polymer-based organic solar cells (OSCs) offer a cost-effective option for solar energy conver- sion and are attractive as a solution-processable alternative to classical inorganic photovoltaic solutions. The most commonly used materials for polymeric solar cell fabrication are Poly(3-hexylthiophen-2,5-diyl) (P3HT) as electron donor and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as electron acceptor [1]. Recent reports have shown that this material combination can reach power conve...

Near-Infrared Organic Photodiodes

Organic photodiodes (OPDs) are attractive as solution-processed devices for sensing applications. Industrial and medical sensors often have the requirement to operate in the near-infrared (NIR) spectrum between 650 and 900 nm and are ideally visible-blind. Due to the tailored spectral sensitivity of the organic semiconductors, OPDs are attractive as filter-free solidstate alternative. In addition, the large active areas of the OPDs potentially allow fabricating lens-free light-barrier and reflective sensors. In this paper, we discuss different approaches toward NIR sensitive OPDs with a large active area up to 1 cm/sup2sup/ applying polymers and small molecules as light absorbers. We demonstrate that with layer stacks optimized to the solution-processed semiconductor properties photodiodes with bulk heterojunctions with a minimum external quantum efficiency peak >40% in the NIR and a rectification ratio of ∼10/sup5sup/ can be achieved, which match industrial sensing requirements.

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Francesco Arca (@Francesco)
Published in 
 · 13 May 2018
Fig. 1. OPDs with NIR sensitivity. a) OPD layer stack. NIR light is applied to the OPD through the t
I. INTRODUCTION SOLUTION-processed OPDs with NIR sensitivity are an attractive replacement for solid-state photosensors due to the cost-effective processing. Si or InGaAs sensors are usually applied to cover the industrially-relevant spectral region between ∼650 nm and ∼900 nm wavelengths beyond the spectral sensitivity of the human eye. Unfortunately, these solid-state devices show a broad spectral response in both the visible and the NIR range which requires filtering. For many applications such as light barriers or reflective sensors only the NIR sensitivity is needed since photodetectors are usually used in ambient condition with vis...

Large Active Area Organic Photodiodes for Short-Pulse X-ray Detection

Organic thin film light sensors are promising devices for X-ray imaging systems. Compared to crystalline silicon photodiodes (c-Si), organic sensors can be fabricated on large active area at low cost. Furthermore, organic semiconductors have the advantage of low X-ray absorption. Here, we show that despite the high diode capacitance of several nF/cm/sup2sup/, a single X-ray pulse detection as low as ∼14 µGy can be detected in the ms regime. Such device properties match industrial requirements for X-ray sensing.

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Francesco Arca (@Francesco)
Published in 
 · 15 Apr 2018
Fig. 1. (a) OPD layer stack with scintillator for X-ray detection. (b) IV measurement in dark and un
I. INTRODUCTION Organic electronics is attractive for fabrication of solution-processed photodiodes at low temperatures with large active areas even on flexible substrates with a variety of geometrical degrees of freedom [1]. In addition, the spectral sensitivities of the devices can be tailored with the organic semiconductor absorber for the respective application [2]. Such low-effort and low-cost processing conditions are of interest for sensing with >1 cm 2 organic photodetectors as potential replacement of silicon photodiodes [1] [2] since large active areas of several cm 2 are difficult to achieve with solid-state devices. In partic...

Interface Trap States in Organic Photodiodes

Organic semiconductors are attractive for optical sensing applications due to the effortless processing on large active area of several cm/sup2sup/, which is difficult to achieve with solid-state devices. However, compared to silicon photodiodes, sensitivity and dynamic behavior remain a major challenge with organic sensors. Here, we show that charge trapping phenomena deteriorate the bandwidth of organic photodiodes (OPDs) to a few Hz at low-light levels. We demonstrate that, despite the large OPD capacitances of ~10 nF cm/sup−2sup/, a frequency response in the kHz regime can be achieved at light levels as low as 20 nW cm/sup−2sup/ by appropriate interface engineering, which corresponds to a 1000-fold increase compared to state-of-the-art OPDs. Such device characteristics indicate that large active area OPDs are suitable for industrial sensing and even match medical requirements for single X-ray pulse detection in the millisecond range.

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Francesco Arca (@Francesco)
Published in 
 · 8 Apr 2018
Figure 1 | Organic photodiode layout with 1 cm/sup2sup/ active area, electrical characteristics, and
X-ray radiation detection is a key application in medical diagnostics and requires highly sensitive detectors to ensure both high image quality and low patient dose. In general the detection is performed by indirect X-ray conversion using a thin film scintillator material, such as terbium-doped gadolinium oxysulfide (GOS:Tb or GOS), to generate fluorescence at a wavelength that matches the spectral sensitivity of radiographic films or amorphous silicon (a-Si) photodiodes. Due to optic limitations to concentrate more X-ray photons into a small area, X-ray photodetectors have to be large devices of several cm 2 for sufficient sensitivity. I...
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