2015: Unnoticed advantage of organic solar cells�

MSU physicists discovered that one of the key photovoltaic parameters of organic solar cells can exceed the Shockley-Queisser limit.

Organic solar cells are promising alternative to silicon and other inorganic solar cells due to the ease of fabrication, low cost, low weight and mechanical flexibility. However, the efficiency of the best organic solar cells nowadays is significantly lower than that for inorganic ones. The ultimate efficiency of organic solar cells is suggested to be always lower than that of single-junction inorganic solar cells according to the so-called Shockley-Queisser limit (1961). The solar cell efficiency is calculated from its current-voltage (I-V) characteristic upon illumination, it is proportional to the area of a rectangle inscribed in the fourth quadrant of the I-V characteristics. The efficiency is strongly dependent on the steepness of the IV curve, which is characterized by a fill factor (FF). Shockley and Queisser also established a theoretical limit for FF of inorganic solar cells.�

Using a recently developed numerical model of organic solar cells, which takes into account the features of photogeneration, transport and recombination of charge carriers in organic semiconductors [V.A. Trukhanov, et al., Phys.Rev.B 84, 205318 (2011)], a group of physicists from the Moscow State University has shown that the FF for organic solar cells may exceed the Shockley-Queisser limit. This finding highlights a previously unnoticed advantage of organic solar cells and suggests the ways of their improvement.�

The results are published in: V.A. Trukhanov, V.V. Bruevich, D.Yu. Paraschuk "Fill factor of organic solar cells can exceed the Shockley-Queisser limit,” Scientific Reports�5, 11478 (2015).