Thin Film Solar Cell Design Concept

This is some more tweaking ofsolar cell tech and should lead to further improvements in economics andgeneral efficiencies.  Solar techcontinues to be stalled in much the same place it has held for a decade, inspite of plenty of brave announcements by venture capitalists.

It needs either a breakthrough inspectrum absorption and conversion or a significant drop in manufacturingcost.  At this late date I do not holdout much optimism when it will all be scrap when they start shipping eighttimes unity reactor from Rossi Focardi.

In the meantime we continue towatch these efforts.

'Swiss cheese' design enables thin film silicon solar cellswith potential for higher efficiencies

by Staff Writers

College Park, MD (SPX) May 10, 2011

This SEM micrograph shows the nanostructured ZnO layer, Swiss cheesedesign for Micromorph solar cells.Credit: Milan Vanecek, Instituteof Physics, Prague

http://www.solardaily.com/reports/Swiss_cheese_design_enables_thin_film_silicon_solar_cells_with_potential_for_higher_efficiencies_999.html

A bold new design for thin film solar cells that requires significantly lesssilicon - and may boost their efficiency - is the result of anindustry/academia collaboration between Oerlikon Solar in Switzerland and theInstitute of Physics'photovoltaic groupat the Academy of Sciences of the Czech Republic.

One long-term option for low-cost, high-yield industrial productionof solarpanels fromabundant raw materials can be found in amorphous silicon solar cells andmicrocrystalline silicon tandem cells (a.k.a. Micromorph)-providing an energypayback within a year.

A drawback to these cells, however, is that the stable panel efficiencyis less than the efficiency of presently dominate crystalline wafer-basedsilicon, explains Milan Vanecek, who heads thephotovoltaic group at the Institute ofPhysics in Prague.

"To make amorphous and microcrystalline silicon cells more stablethey're required to be very thin because of tight spacing between electricalcontacts, and the resulting optical absorption isn't sufficient," henotes.

"They're basically planar devices. Amorphous silicon has athickness of 200 to 300 nanometers, while microcrystalline silicon is thickerthan 1 micrometer."

The team's new design focuses on optically thick cells that arestrongly absorbing, while the distance between the electrodes remains verytight. They describe their design in the American Institute of Physics' journalApplied Physics Letters.

"Our new 3D design of solar cells relies on the mature, robustabsorber deposition technology of plasma-enhanced chemical vapor deposition, whichis a technology already used for amorphous silicon-based electronics producedfor liquid crystal displays. We just added a new nanostructured substratefor the deposition of the solar cell," Vanecek says.

This nanostructured substrate consists of an array of zinc oxide (ZnO)nanocolumns or, alternatively, from a "Swiss cheese" honeycomb arrayof micro-holes or nano-holes etched into the transparent conductive oxide layer(ZnO) (See Figure).

"This latter approach proved successful for solar cell deposition,"Vanecek elaborates.

"The potential of these efficiencies is estimated within the rangeof present multicrystalline wafer solar cells, which dominate solar cellindustrial production. And the significantly lower cost of Micromorph panels,with the same panel efficiency as multicrystalline silicon panels (12 to 16percent), could boost its industrial-scale production."

The next step is a further optimization to continue improvingefficiency.

The article, "Nanostructured 3-dimensional thin film silicon solarcells with very high efficiency potential," by Milan Vanecek, Oleg Babchenko, Adam Purkrt,Jakub Holovsky, Neda Neykova, Ales Poruba, Zdenek Remes, Johannes Meier, and UlrichKroll, appears in the journal Applied Physics Letters.