ON THE THICKNESS DEPENDENCE OF OPEN-CIRCUIT VOLTAGES OF P-N-JUNCTION SOLAR-CELLS

A reduction of the thickness of solar cells with low surface recombination is known to result in enhanced open circuit voltages, provided that the short circuit current can be maintained sufficiently high by light trapping schemes. Lower volume recombination is generally assumed to cause this effect. We offer another interpretation: The voltage increases because thinning the cell at constant short circuit current enhances the minority carrier generation rate per unit volume and hence the steady state carrier concentration. Thermodynamically, an increased carrier concentration is equivalent to a reduction of the entropy production per photon, thus leading to larger voltage.