Materials processing strategies for colloidal quantum dot solar cells: advances, present-day limitations, and pathways t
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Materials processing strategies for colloidal quantum dot solar cells: advances, present-day limitations, and pathways to improvement Graham H. Carey, Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada Kang W. Chou, Buyi Yan, Ahmad R. Kirmani, and Aram Amassian, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia Edward H. Sargent, Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada Address all correspondence to Edward H. Sargent at [email protected] (Received 22 January 2013; accepted 25 April 2013)
Abstract Colloidal quantum dot photovoltaic devices have improved from initial, sub-1% solar power conversion efficiency to current record performance of over 7%. Rapid advances in materials processing and device physics have driven this impressive performance progress. The highestefficiency approaches rely on a fabrication process that starts with nanocrystals in solution, initially capped with long organic molecules. This solution is deposited and the resultant film is treated using a solution containing a second, shorter capping ligand, leading to a cross-linked, non-redispersible, and dense layer. This procedure is repeated, leading to the widely employed layer-by-layer solid-state ligand exchange. We will review the properties and features of this process, and will also discuss innovative pathways to creating even higher-performing films and photovoltaic devices.
The most abundant and cleanest source of energy available on Earth, solar energy, is also the most underutilized. Its peak intensity is 1000 W/m2 which, averaged over space and time, provides vastly more energy daily than the global population consumes. Solar energy thus offers, in principle, a compelling option to power a sustainable and increasingly electricitycentric future.[1] While a substantial photovoltaic industry is beginning to take shape worldwide, driven by early generation solar technology based on silicon and compound semiconductors such as cadmium telluride, the fact remains that, in order to compete with traditional energy sources, particularly with cheap and plentiful natural gas, solar photovoltaic systems must cost, fully installed, no more than $1 per watt-peak, which translates to a levelized cost of electricity of approximately $0.05/kWh over a system lifetime.[2] This is noticeably less than current first- and second-generation commercially available solar products, which are held back by higher materials and manufacturing costs; combined with installation costs influenced by the bulky, heavy, and rigid nature of the solar panels themselves. Third-generation photovoltaic systems, including organic, dye-sensitized, and colloidal quantum dot (CQD) solar cells, offer a path to low-weight, low-cost, and prospectively highefficiency solar energy capture and conversion. While th
