meen 489 689 lecture 10 nanomaterials in emerging energy sectors and their applications
Post on 12-Feb-2017
249 Views
Preview:
TRANSCRIPT
1
MEEN 489/689: Entrepreneurship & Nanomaterials for Energy Applications
Lecture 10 Nanomaterials in Emerging Energy Sectors & Applications
James Donnell, Andreas Polycarpou,Tanil Ozkan, Haejune Kim
Fall 2015
10/1/2015
2MEEN 489/689
http://www.adnjusa.com
MEEN 489/689 Source : Hessen Nanotech 2008
4MEEN 489/689
http://www.adnjusa.com
5MEEN 489/689
http://www.adnjusa.com
6MEEN 489/689
http://www.adnjusa.com
7MEEN 489/689
http://www.adnjusa.com
MEEN 489/689
Photovoltaics
9MEEN 489/689
http://www.adnjusa.com
10MEEN 489/689
http://www.adnjusa.com
https://www.youtube.com/watch?v=JBtEckh3L9Q
11MEEN 489/689
http://www.adnjusa.com
www.youtube.com/watch?v=K76r41jaGJg
MEEN 489/689
Solar Cell – Operating Principles
A photon from the Sun generates an electron-hole pair in a semiconductor. The electron is pulled to the front, the hole to the back of the solar cell, thereby creating a battery.
MEEN 489/689
Energy diagram of a solar cell
The electron and hole are pulled apart by the electric field between the p- and n-doped regions. It is critical not to lose electrons and holes on their way out. Crystalline semiconductors are good at that, but expensive.
Energy
14MEEN 489/689
http://www.adnjusa.com
Efficiency limits: 30% for a single junction (Shockley-Queisser limit) 70% for multiple junctions
MEEN 489/689
Electrons, Holes, and Excitons
A photon excites an electron across the band gap of a semiconductor.
That leaves a hole among the occupied levels in the valence band and an electron among the unoccupied levels in the conduction band.
Electron and hole are attracted electrically and can form an exciton (similar to a hydrogen atom). In organic semiconductors it takes a significant amount of energy to break them apart into free carriers.
PhotonElectron
Hole
Energy
Band Gap
exciton
MEEN 489/689
Thin film solar cells
• Compound semiconductors: CdTe, CIGS = Cu(InGa)Se• Less material, less energy by low temperature processing• Print solar cells like newspaper (roll-to-roll)
Solar cell printed on plastic
Nanosolar (San Jose, Berlin)
MEEN 489/689
Nanostructured solar cells
Use nanostructured “fractal” structures to minimize the path of excitons, electrons, holes, to the nearest electrode. Avoid losses.
Better design: Regular array of nanorods
MEEN 489/689
ZnO nanorods as electrode
Growth time increases from left to right.
(a)-(c) side view (500 nm bar), (d)-(f) top view (100 nm bar). Baxter et al., Nanotechnology 17, S304 (2006) and Appl. Phys. Lett. 86, 053114 (2005).
MEEN 489/689
Nanorods coated with nanocrystals
CsSe nanodots (3 nm) replace the dye. Absorption spectrum tunable via the size of the dot. More robust against radiation
damage.Leschkies et al., Nano Letters 7, 1793 (2007).
MEEN 489/689
MEEN 489/689
Solar thermalConvert solar energy to steam, then to electricity
MEEN 489/689
MEEN 489/689
Thermoelectrics
MEEN 489/689
Efficiency of Thermoelectric Materials(figure of merit ZT)
MEEN 489/689
What materials have high ZT?
MEEN 489/689
Nanoscale effects with thermoelectric conversion
MEEN 489/689
Nanoscale effects with thermoelectric conversion
MEEN 489/689
Thermoelectric waste heat recovery systems
MEEN 489/689
Thermoelectric waste heat recovery systems
https://gsuryalss.wordpress.com/tag/thermoelectric-material/
top related