Tobias Rauch

Temperature dependent photoresponse from colloidal PbS quantum dot sensitized inorganic/organic hybrid photodiodes

Inorganic/organic hybrid photodiodes, based on a solution-processed ternary blend containing PbS quantum dots (QDs), a fullerene derivative, and a conjugated polymer, have been reported to exhibit external quantum efficiencies in the infrared of up to 51% [T. Rauch et al., Nat. Photonics 3, 332 (2009)]. Temperature dependent experiments reveal the high sensitivity of the photoresponse on the energy level alignment between the QDs and the fullerene derivative, resulting in quenching of the photoresponse at low temperatures for 5.2 nm QDs in size. With smaller QDs the optimum operation temperature is found between room temperature and 72 °C, making these photodiodes promising for various applications.

Design of Highly Transparent Organic Photodiodes

In this brief, various approaches for the realization of transparent photodiodes based on bulk heterojunction blends of poly-3-hexylthiophene and [6,6]-phenyl C61-butyric acid methyl ester are studied. The choice of the constituents of the device is discussed concerning transmittance and light-detecting properties as dark current and external quantum efficiency (EQE). Blending several light-absorbing materials makes tailoring of the transmittance spectrum possible. Transmittance of 36% of the incident light together with 46% EQE at a wavelength of 530 nm are promising results and show the potential for highly transparent photodiodes based on organic layers.

Performance of bulk-heterojunction organic photodetectors

The performance of organic photodetectors has already reached a high level. In the near future organic photodetectors can be found in applications like imaging and sensing. The core of organic photodetectors is the bulk-heterojunction. Fullerenes and conjugated polymers forming islands in nanometer size are causing the outstanding quantum efficiencies. The conjugated polymers have a high absorption coefficient and the fullerenes are efficiently transferred electrons from the polymer. This leads to a high sensitivity to light. Organic photodetectors with low dark currents, external quantum efficiencies of 80% in the visible, linearity over several decades and fast transient behavior are demonstrated.