Near infrared organic photodetector utilizing a double electron blocking layer

High-Performance Near-Infrared-Selective Thin Film Organic Photodiode Based on a Molecular Approach Targeted to Ideal Semiconductor Junctions

A molecular approach to achieve wide linear dynamic range (LDR) and near-infrared (NIR)-selective thin film organic photodiodes (OPDs) with high detectivity is reported. Comparative studies based on two NIR-selective polymers are systematically investigated: the commercially available poly[(4,4'-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b']dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTBT) and the synthesized poly[(4,4'-(bis(hexyldecylsulfanyl)methylene)cyclopenta[2,1-b:3,4-b']-dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTSBT). The introduction of sp²-hybridized side chains in the PCPDTSBT structure can improve chain planarity and thus intermolecular interactions, as confirmed by Raman spectroscopy and grazing incidence X-ray diffraction studies. The favorable crystalline orientation of PCPDTSBT leads to enhanced photocurrent and suppressed noise current, compared to that of PCPDTBT, followed by a sharp increase in the specific detectivity of PCPDTSBT-based NIR OPDs by 1.54 × 10¹² Jones. The physics behind PCPDTSBT is analyzed employing optical simulation, temperature-dependent junction analyses, and Mott-Schottky analysis. Furthermore, it is found that PCPDTSBT possesses an exceptional nonsaturation photocurrent, which leads to a wide LDR of 128 dB. This study shows the possibility of realizing thin film NIR-selective OPDs using synthetic approaches.

Green-light-selective organic photodiodes for full-color imaging

In this work, organic photodiodes (OPDs) based on two newly synthesized p-type dipolar small molecules are reported for application to green-light-selective OPDs. In order to reduce the blue-color absorption induced by the use of C60 as the n-type material in a bulk heterojunction (BHJ), the electron donor:electron acceptor composition ratio is tuned in the BHJ. With this light manipulation approach, the blue-wavelength external quantum efficiency (EQE) is minimized to 18% after reducing the C60 concentration in the center part of the BHJ. The two p-type molecules get a cyanine-like character with intense and sharp absorption in the green color by adjusting the strength of their donating and accepting parts and by choosing a selenophene unit as a π-linker. When combined to C60, the green-wavelength EQE reaches 70% in a complete device composed of two transparent electrodes. Finally, the optical simulation shows the good color-balance performance of hybrid full-color image sensor without an additional filter by using the developed green OPD as the top-layer in stacked device architecture.

Universal Strategy To Reduce Noise Current for Sensitive Organic Photodetectors

Low noise current is critical for achieving high-detectivity organic photodetectors. Inserting charge-blocking layers is an effective approach to suppress the reverse-biased dark current. However, in solution-processed organic photodetectors, the charge-transport material needs to be dissolved in solvents that do not dissolve the underneath light-absorbing layer, which is not always possible for all kinds of light-absorbing materials developed. Here, we introduce a universal strategy of transfer-printing a conjugated polymer, poly(3-hexylthiophene) (P3HT), as the electron-blocking layer to realize highly sensitive photodetectors. The transfer-printed P3HT layers substantially and universally reduced the reverse-biased dark current by about 3 orders of magnitude for various photodetectors with different active layers. These photodetectors can detect the light signal as weak as several picowatts per square centimeter, and the device detectivity is over 10¹² Jones. The results suggest that the strategy of transfer-printing P3HT films as the electron-blocking layer is universal and effective for the fabrication of sensitive organic photodetectors.