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 "The fundamental limit to photovoltaic efficiency is widely thought to be radiative recombination which balances radiative absorption. We here show that it is possible to break detailed balance via quantum coherence, as in the case of lasing without inversion and the photo-Carnot quantum heat engine. This yields, in principle, a quantum limit to photovoltaic operation which can exceed the classical one. The present work is in complete accord with the laws of thermodynamics. ...

We begin by briefly reviewing the underlying physics germane to the present Letter, namely, (1) lasing without inversion (LWI) and (2) photocell operation. Then we show how to combine quantum coherence and cavity quantum electrodynamics to, in principle, make a quantum dot photodiode in a cavity more efficient [4]. ... the only recombination mechanism of electron hole pairs is radiative as required by the principle of detailed balance.’’ Indeed it was on this basis of such detailed balance arguments that Einstein introduced the concept of stimulated emission in the early part of the twentieth century. And when we have population inversion, i.e., negative tem-peratures [6], laser or maser action obtains [7]. However, by the end of the century, it was predicted theoretically [8] and demonstrated experimentally [9] that it is possible to break detailed balance and cancel stimulated absorption, while keeping stimulated emission ...  it is possible to prepare a coherent doublet in the excited state and again break detailed balance ...quantum coherence could (in principle) be used to mitigate radiative recombination in a solar cell, let us first analyze the quantum dot cell ... In the present Letter, we use quantum coherence to enhance the transfer of solar energy to the quantum dots. In the quantum photo-Carnot engine, we use quantum coherence to maximize transfer of atomic energy to the photons.


To summarize, we return to the question, ‘‘Can radiation recombination be avoided?’’ The answer is yes, in principle. By breaking detailed balance, radiative rec ombinations can be substantially reduced. This can, in principle, enhance the efficiency of photocells, e.g., photodetectors and solar cells ..."

PRL 104, 207701 (2010)

PHYSICAL REVIEW LETTERS week ending 21 MAY 2010

Quantum Photocell: Using Quantum Coherence to Reduce Radiative Recombination and Increase Efficiency

Marlan O. Scully

Texas A&M University, College Station, Texas 77843, USA Princeton University, Princeton, New Jersey 08544, USA (Received 18 November 2009; published 21 May 2010)