The limiting factors on the efficiency of current record devices are discussed. Optical and collection losses are found to have a minor influence. They reduce the short circuit current. Higher losses are due to recombination losses. The defects responsible for Shockley-Read-Hall recombination are discussed, and it is concluded that Shockley-Read-Hall recombination is not likely the source for the open circuit voltage loss. However the recombination is increased by inhomogeneities. Inhomogeneities of the band gap can be excluded, because they are too small to have significant influence. Electrostatic potential variations at charged extended defects like grain boundaries are however responsible for losses in the open circuit voltage. (C) 2010 Elsevier B.V. All rights reserved.