High efficiency homojunction InP solar cells

Homojunction InP solar cells with a high conversion efficiency of 18.0% have been fabricated using thermal diffusion of sulphur into p-type InP. An open-circuit voltage Voc as high as 0.837 V which resulted from a reduction in leakage current was attained by employing mesa etching as a method for sectioning cells on a diffused wafer. Fill factor was also increased to 82.9% owing to both a small diode ideality factor (≲1.3) and a low cell series resistance (≲0.5 Ω cm2). As a result of the improvement in these factors, a conversion efficiency as high as 18.0% (an active-area conversion efficiency of 20.1%) under AM1.5 illumination was obtained. A phenomenon whereby shunt resistance in a mesa-etched cell is reduced by illumination is discussed. This is due to the additional current flowing from the peripheral p-InP region bared by the mesa etching.