Predicted outdoor energy yield of Si based tandem solar cells

Abstract

Silicon based tandem solar cells have recently received a lot of attention. They are promising candidates to provide the next efficiency boost at moderate fabrication costs. This potentially enables their application in non-concentrating PV systems. It is known that tandem solar cells are sensitive to outdoor irradiation variations, which are more pronounced for non-concentrating applications. Therefore it is important to assess their yield under realistic operating conditions. In this work we analyze the distribution of outdoor conditions measured in Singapore, and calculate the device efficiency losses for these conditions. We find that 2 terminal tandem devices suffer substantially from current mismatch losses, which can amount to 3% to 5% of the rated efficiency under standard testing conditions (STC). Despite this, the predicted performance ratio for tandem solar cell is still on par or better than conventional single-junction Si solar cells. Adjusting the top cell thickness to match the current of the bottom cell under the average Singapore spectrum can decrease the loss due to current mismatch and increase overall yield by 0.8% to 1.7%.