How Thin Practical Silicon Heterojunction Solar Cells Could Be? Experimental Study under 1 Sun and under Indoor Illumination

The transition toward thinner microcrystalline silicon wafers for their potential performance gain has been of interest in recent years. Theoretical predictions have estimated a maximum efficiency for silicon wafers to be at about 100-110 mu m thickness. The potential and losses in silicon heterojunction solar cells prepared on wafers with thickness in the range of 60-170 mu m with focus on open-circuit voltage (V-OC) and fill factor (FF) are studied experimentally. The applicability of thinner wafers for low light and indoor applications using light emitting diode (LED) lighting is also studied. The implied V-OC (iV(OC)) is observed to increase with a decrease in wafer thickness according to theoretical predictions with absolute values approaching the theoretical limit. Unlike the iV(OC), the implied FF is observed to decrease with wafer thickness reduction opposite to the theoretical predictions which are related to the effect of surface recombination. A combination of gains and losses results in a broad range of high efficiency under 1 sun for wafer thicknesses ranging from 75 to 170 mu m with maximum of 22.3% obtained at 75 mu m. As for indoor performance, thinner wafers show slightly better efficiency at lower light intensity under sun and LED illumination, promising improved performance for even thinner devices.