New Way to Thinner Photodiodes

A new type of thin-film photodiode made of perowskites. (Source: DGIST)

A research team of Energy Science and Engi­neering at Daegu Gyeongbuk Insti­tute of Science & Techno­logy DGIST has unveiled a new high-perfor­mance photo­diode that reduces thickness to one-sixth of conven­tional silicon photo­diodes. According to the researchers, the key is to develop a tech­nology that can increase the stabi­lity and perfor­mance of photo­diodes using cubic perovskite nano­crystals. Applying this techno­logy to future photo­diodes will contribute to the fields that require high accu­mulation and reso­lution.

Silicon photo­diodes, the basic photo­electric conversion units of image sensors, are regarded as the mainstay for a variety of imaging appli­cations because of their low noise, wide bandwidth absorption, and high operating frequency. None­theless, the silicon photo­diodes currently in use in industry have limited reso­lution enhance­ment due to their thick­nesses exceeding 3 micro­meters. Perovs­kite, which is one of the main materials to replace them, absorbs light well, but it was difficult to put it into practical use due to its low stabi­lity.

As a way to overcome the disad­vantages of the existing materials, Dae Sung Chung paid attention to the fact that cesium lead iodide perovs­kite maintains stabi­lity in the form of cubic nano­crystals. The research team has developed a new type of thin-film photo­diode utilizing cubic cesium lead iodide perovskite nano­crystals and sulfur compounds between the electrodes of the photodiode. The photo­diodes developed by the team have improved stabi­lity through acid-base reactions between plumbum ions and sulfur anions.

The optimized 0.5 micro­meter thick thin-film photo­diode demon­strated a very high sensi­tivity, similar to a silicon photo­diode. In addition, it was stably operated for more than 10 hours even under the harsh conditions of relative humi­dity of over 80 percent. The researchers suggested a method to improve the stabi­lity of various optical devices such as light emitting diodes and solar cells using perovskite as well as photo­diodes. Further­more, cesium lead iodide perovskite nano­crystals are expected to be used in various ubi­quitous fields as they are able to be processed at low tempera­tures.

“The small and high-perfor­mance photo­diodes developed by this research will be applicable to auto­nomous vehicles, military and space explo­ration fields that require high accu­mulation and reso­lution,” said Chung. “We will continue to lead the forth indus­trial revo­lution by develo­ping low-cost, high-effi­ciency, and high-stabi­lity image sensors using perovskite photo­diodes.” (Source: DGIST)

Reference: K. M. Sim et al.: Phase Stabilized α-CsPbI3 Perovskite Nanocrystals for Photodiode Applications, Laser & Phot. Rev., online 6 November 2017; DOI: 10.1002/lpor.201700209

Link: Eco Energy Device Lab, Daegu Gyeongbuk Inst. of Science & Tech. DGIST, Daegu, Republic of Korea

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