Issue 3, 2012

Photovoltaic efficiency limits and material disorder

Abstract

Solar cells based on crystalline semiconductors such as Si and GaAs provide nowadays the highest performance, but photovoltaic (PV) cells based on less pure materials, such as poly- or nano-crystalline or amorphous inorganic or organic materials, or a combination of these, should relax production requirements and lower the cost towards reliable, sustainable and economic electrical power from sunlight. So as to be able to compare the operation of different classes of solar cells we first summarize general photovoltaic principles and then consider implications of using less than ideal materials. In general, lower material purity means more disorder, which introduces a broad distribution of energy states of the electronic carriers that affects all the aspects of PV performance, from light absorption to the generation of voltage and current. Specifically, disorder penalizes energy output by enhanced recombination, with respect to the radiative limit, and also imposes a lowering of quasi-Fermi levels into the gap, which decreases their separation, i.e., reduces the photovoltage. In solar cells based on organic absorbers, such as dye-sensitized or bulk heterojunction solar cells, vibronic effects cause relaxation of carriers in the absorber, which implies an energy price in terms of obtainable output.

Graphical abstract: Photovoltaic efficiency limits and material disorder

Article information

Article type
Perspective
Submitted
15 Nov 2011
Accepted
06 Jan 2012
First published
06 Jan 2012

Energy Environ. Sci., 2012,5, 6022-6039

Photovoltaic efficiency limits and material disorder

P. K. Nayak, G. Garcia-Belmonte, A. Kahn, J. Bisquert and D. Cahen, Energy Environ. Sci., 2012, 5, 6022 DOI: 10.1039/C2EE03178G

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