A thermodynamic cycle for the solar cell
  A solar cell is a heat engine, but textbook treatments are not wholly satisfactory from a thermodynamic standpoint, since they present solar cells as directly converting the energy of light into electricity, and the current in the circuit as maintained by an electrostatic potential. We propose a thermodynamic cycle in which the gas of electrons in the p phase serves as the working substance. The interface between the p and n phases acts as a self-oscillating piston that modulates the absorption of heat from the photons so that it may perform a net positive work during a complete cycle of its motion, in accordance with the laws of thermodynamics. We draw a simple hydrodynamical analogy between this model and the "putt-putt"' engine of toy boats, in which the interface between the water's liquid and gas phases serves as the piston. We point out some testable consequences of this model. 
Robert Alicki, David Gelbwaser-Klimovsky and Alejandro Jenkins
cond-mat.stat-mech quant-ph