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 recombina tion is known to result in enhanced open circuit voltages, provided th at the short circuit current can be maintained sufficiently high by li ght trapping schemes. Lower volume recombination is generally assumed to cause this effect. We offer another interpretation: The voltage inc reases because thinning the cell at constant short circuit current enh ances the minority carrier generation rate per unit volume and hence t he steady state carrier concentration. Thermodynamically, an increased carrier concentration is equivalent to a reduction of the entropy pro duction per photon, thus leading to larger voltage.