{"id":5057,"date":"2011-12-26T13:40:11","date_gmt":"2011-12-26T20:40:11","guid":{"rendered":"http:\/\/cafe.foundation\/blog\/?p=5057"},"modified":"2011-12-26T13:47:37","modified_gmt":"2011-12-26T20:47:37","slug":"going-over-to-the-dark-side","status":"publish","type":"post","link":"http:\/\/cafe.foundation\/blog\/going-over-to-the-dark-side\/","title":{"rendered":"Going Over to the Dark Side"},"content":{"rendered":"

The University of Texas at Austin\u2019s press release <\/a>spells out the quantum-like behavior of photons striking solar cells, and provides some insight into why obtaining higher efficiencies so far has perplexed researchers.<\/p>\n

\u201cAUSTIN, Texas \u2014 The efficiency of conventional solar cells could be significantly increased, according to new research on the mechanisms of solar energy conversion led by chemist Xiaoyang Zhu<\/a> at The University of Texas at Austin.<\/p>\n

\u201cZhu and his team have discovered that it’s possible to double the number of electrons harvested from one photon of sunlight using an organic plastic semiconductor material.<\/p>\n

“\u2019Plastic semiconductor solar cell production has great advantages, one of which is low cost,\u2019 said Zhu, a professor of chemistry. \u2018Combined with the vast capabilities for molecular design and synthesis, our discovery opens the door to an exciting new approach for solar energy conversion, leading to much higher efficiencies.\u2019”<\/p>\n

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Pentacene stick and ball model<\/p><\/div>\n

Zhu and his team published their discovery December 16 in the journal Science<\/em><\/a>, under the title \u201cObserving the Multiexciton State in Singlet Fission and Ensuing Ultrafast Multielectron Transfer,\u201d although the abstract may bring more darkness than light to this modest attempt to enlighten.<\/p>\n

\u201cMultiple exciton generation (MEG) refers to the creation of two or more electron-hole pairs from the absorption of one photon. Although MEG holds great promise, it has proven challenging to implement, and questions remain about the underlying photo-physical dynamics in nanocrystalline as well as molecular media. Using the model system of pentacene\/fullerene bilayers and femtosecond nonlinear spectroscopies, we directly observed the multiexciton (ME) state ensuing from singlet fission (a molecular manifestation of MEG) in pentacene. The data suggest that the state exists in coherent superposition with the singlet populated by optical excitation.\u00a0 We also found that multiple electron transfer from the ME state to the fullerene occurs on a subpicosecond time scale, which is one order of magnitude faster than that from the triplet exciton state.\u201d<\/em><\/p>\n

The maximum theoretical efficiency of the silicon solar cell in use today is approximately 31 percent, because much of the sun’s energy hitting the cell is too high to be turned into usable electricity. That energy, in the form of “hot electrons,” is instead lost as heat. Capturing hot electrons \u201ccould potentially increase the efficiency of solar-to-electric power conversion to as high as 66 percent.\u201d<\/p>\n

The press release provides a four-point explanation of the quirky behavior that now limits solar cell efficiency, but also shows how the current causes of the waste heat could be exploited for greater gain.<\/p>\n