Ph.D. Dissertation Defense: Yangyi Yao

Tuesday, April 30, 2019
3:30 p.m.-5:30 p.m.
AVW 2460
Maria Hoo
301 405 3681

ANNOUNCEMENT: Ph.D. Dissertation Defense

NAME: Yangyi Yao
Advisory Committee:
Professor Mario Dagenais, Chair/Advisor
Professor Edo Waks
Professor Martin Peckerar
Professor Kevin Daniels
Professor Marina Leite  
Professor  Lourdes Salamanca-Riba,  Dean's representative
Date/Time: Tuesday, April 30th, 3:30 - 5:30pm.
Place: AVW 2460
Title: Fabrication and Characterization of Perovskite and Intermediate Band InAs/GaAs Quantum Dot Solar Cells
Metal-organic perovskite materials have outstanding properties in photovoltaic applications, the perovskite based solar cells s have already demonstrated remarkable power conversion efficiency enhancement from 3.8%  in 2009 to 23.7% in late 2018. In our work, we focused on the simple PTAA-based planar perovskite solar cell without using a complicated surface passivation technique. We proposed a sequential method to dope the PTAA thin film in order to reduce the solar cell’s series resistance. We also modified the inter-diffusion growth method to grow high quality perovskite thin films, we can easily grow the perovskite thin film layer with thicknesses over 400 nm and grain sizes over 2 mm. Compared to our conventional PEDOT:PSS based perovskite solar cell, we observed an improvement in both the open-circuit-voltage and the short-circuit current, resulting in a power conversion efficiency enhancement from 12.7% to 15.3%. Other applications of perovskite material such as perovskite tandem cell and perovskite-based laser cavity are also investigated.
The concept of intermediate band solar cell was proposed by Luque and Marti in 1990 and has been extensively studied for decades. Previously we have reported high optical saturation intensity of the quantum dot resonance at room temperature for a self-ensemble of un-doped quantum dots (QDs). Operating at cryogenic temperatures leads to a reduction of the saturation intensity. We acquired a liquid-helium cryo-cooler system to support the on-resonance measurement of the quantum dot solar cell (QDSC) at cryogenic temperatures. We measured the photoluminescence of the QDSC to extract the QD energy from 293K to 8K. We modified the on-resonance z-scan set-up with the cryo-cooler to evaluate the saturation effects of the QDs. We studied the photocurrent response and extracted the saturation intensity of the QD ground state from 293K to 170K. We observed a substantial decrease of the saturation intensity as the temperature is decreased, but this intensity is still much higher than one-sun intensity. The intermediate band two photon absorption contribution to the photocurrent enhancement is extremely small even at 170K. By cooling all the way down to liquid helium temperatures, it should be possible to further reduce the saturation intensity.


Audience: Graduate  Faculty 


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