Media Releases

U of T Engineering breakthrough promises significantly more efficient solar cells

March 7, 2013

TORONTO, ON – A new tech­nique devel­oped by Uni­ver­si­ty of Toron­to Engi­neer­ing Pro­fes­sor Ted Sar­gent and his research group could lead to sig­nif­i­cant­ly more effi­cient solar cells, accord­ing to a recent paper pub­lished in the jour­nal Nano Let­ters.

The paper, “Joint­ly-tuned plas­mon­ic-exci­ton­ic pho­to­voltaics using nanoshells,” describes a new tech­nique to improve effi­cien­cy in col­loidal quan­tum dot pho­to­voltaics, a tech­nol­o­gy which already promis­es inex­pen­sive, more effi­cient solar cell tech­nol­o­gy. Quan­tum dot pho­to­voltaics offers the poten­tial for low-cost, large-area solar pow­er – how­ev­er these devices are not yet high­ly effi­cient in the infrared por­tion of the sun’s spec­trum, which is respon­si­ble for half of the sun’s pow­er that reach­es the Earth.

The solu­tion? Spec­tral­ly tuned, solu­tion-processed plas­mon­ic nanopar­ti­cles. These par­ti­cles, the researchers say, pro­vide unprece­dent­ed con­trol over light’s prop­a­ga­tion and absorp­tion.

The new tech­nique devel­oped by Sargent’s group shows a pos­si­ble 35 per cent increase in the technology’s effi­cien­cy in the near-infrared spec­tral region, says co-author Dr. Susan­na Thon. Over­all, this could trans­late to an 11 per cent solar pow­er con­ver­sion effi­cien­cy increase, she says, mak­ing quan­tum dot pho­to­voltaics even more attrac­tive as an alter­na­tive to cur­rent solar cell tech­nolo­gies.

“There are two advan­tages to col­loidal quan­tum dots,” Thon says. “First, they’re much cheap­er, so they reduce the cost of elec­tric­i­ty gen­er­a­tion mea­sured in cost per watt of pow­er. But the main advan­tage is that by sim­ply chang­ing the size of the quan­tum dot, you can change its light-absorp­tion spec­trum. Chang­ing the size is very easy, and this size-tun­abil­i­ty is a prop­er­ty shared by plas­mon­ic mate­ri­als: by chang­ing the size of the plas­mon­ic par­ti­cles, we were able to over­lap the absorp­tion and scat­ter­ing spec­tra of these two key class­es of nano­ma­te­ri­als.”

Sargent’s group achieved the increased effi­cien­cy by embed­ding gold nanoshells direct­ly into the quan­tum dot absorber film. Though gold is not usu­al­ly thought of as an eco­nom­i­cal mate­r­i­al, oth­er, low­er-cost met­als can be used to imple­ment the same con­cept proved by Thon and her co-work­ers.

She says the cur­rent research pro­vides a proof of prin­ci­ple. “Peo­ple have tried to do sim­i­lar work but the prob­lem has always been that the met­al they use also absorbs some light and does­n’t con­tribute to the pho­tocur­rent — so it’s just lost light.”

More work needs to be done, she adds. “We want to achieve more opti­miza­tion, and we’re also inter­est­ed in look­ing at cheap­er met­als to build a bet­ter cell. We’d also like to bet­ter tar­get where pho­tons are absorbed in the cell – this is impor­tant pho­to­voltaics because you want to absorb as many pho­tons as you can as close to the charge col­lect­ing elec­trode as you pos­si­bly can.”

The research is also impor­tant because it shows the poten­tial of tun­ing nano­ma­te­r­i­al prop­er­ties to achieve a cer­tain goal, says Paul Weiss, Direc­tor of the Cal­i­for­nia NanoSys­tems Insti­tute.

“This work is a great exam­ple of ful­fill­ing the promise of nanoscience and nan­otech­nol­o­gy,” Weiss says. “By devel­op­ing the means to tune the prop­er­ties of nano­ma­te­ri­als, Sar­gent and his co-work­ers have been able to make sig­nif­i­cant improve­ments in an impor­tant device func­tion, name­ly cap­tur­ing a broad­er range of the solar spec­trum more effec­tive­ly.”


 For more infor­ma­tion, con­tact:

Ter­ry Laven­der
Com­mu­ni­ca­tions & Media Rela­tions Strate­gist
Fac­ul­ty of Applied Sci­ence & Engi­neer­ing
Uni­ver­si­ty of Toron­to
Tel: 416–978-4498