Thin Film Silicon Solar Cells Under Moderate Concentration

Abstract

There are only very few reports on the effects of concentration in thin film siliconbased solar cells. Due to the presence of midgap states, a fast decline in fill factor was observed in earlier work. However, with the advent of more stable and lower defect density protocrystalline silicon materials as well as high quality micro-/nanocrystalline silicon materials, it is worth revisiting the performance of cells with these absorber layers under moderately concentrated sunlight. We determined the behavior of the external J-V parameters of pre-stabilized substrate-type (n-i-p) amorphous and microcrystalline solar cells under moderate concentrations, between 1 sun and 21 suns, while maintaining the cell temperature at 25 o C. It was found that the cell efficiency of both the amorphous and the microcrystalline cells increased with moderate concentration, showing an optimum at approximately 2 suns. Furthermore, the enhancement in efficiency for the microcrystalline cells was larger than for the amorphous cells. We show that the V oc 's up to 0.63 V can be reached in microcrystalline cells while FF's only decrease by 9%. The effects have also been computed using the device simulator ASA, showing qualitative agreement.

Upconverter solar cells: materials and applications

“…13 and 15), because defects increase the sub-band gap density of states. [80][81][82] This is manifested by a drop in the V oc , however this drop in V oc outweighs the increase in current due to light scattering, see Table 2. The transparency of sub-band gap light could be increased by a factor of two by using flat solar cells because the sub-band gap response due to midgap defects is reduced, while there is a concomitant increase in V oc .…”

“…As discussed above, concentration of solar light is a viable option. Adaptation of the solar cell design can improve the incoming light intensity by a factor of 2 to 3 73,80 while solar light concentrations of 300-500 times are reasonable for concentrated PV systems. 83 Alternative options to enhance the upconversion Fig.…”