Towards the Efficiency Limits of Silicon Solar Cells: How Thin Is Too Thin?

Abstract

It is currently possible to fabricate crystalline silicon solar cells with the absorber thickness ranging from a few hundreds of micrometers (conventional wafer-based cells) to devices as thin as 1µm. In this work, we use a model single-junction solar cell to calculate the limits of energy conversion efficiency and estimate the optimal absorber thickness. The limiting efficiency for cells in the thickness range between 40 and 500µm is very similar and close to 29%. In this regard, we argue that decreasing the thickness below around 40µm is counter-productive, as it significantly reduces the maximum achievable efficiency, even when optimal light trapping is implemented. We analyse the roles of incomplete light trapping and extrinsic (bulk and surface) recombination mechanisms. For a reasonably high material quality, consistent with present-day fabrication techniques, the optimal thickness is always higher than a few tens of micrometers. We identify incomplete light trapping and parasitic losses as a major roadblock in improving the efficiency upon the current record of 25.6% for silicon solar cells. Finally, considering the main parameters that impact solar cell performance, we quantify the constraints and requirements for achieving a specified energy conversion efficiency, which is important for a proper designstrategy of high efficiency silicon solar cells.