Conversion Efficiency Analysis of Tandem Solar Cells with Intermediate Band Tunnel Connection

We propose a novel device structure of intermediate band solar cell (IBSC) in which the intermediate band (IB) state is connected to the valence band (VB) of the adjacent bottom cell through a tunnel junction. In this structure, the top cell is an IBSC while the bottom cell is a conventional single gap cell having the identical gap energy to that of top cell conduction band (CB)-IB gap. Detailed balance analysis demonstrated that such IB-tunnel connected tandem cell (IB-TC2) does not require significant CB-IB absorption, and its conversion efficiency less suffers from small shunt resistance connected to the CB-IB diode in the equivalent circuit compared with conventional IBSC with the same bandgap configuration. This new device configuration could be an attractive option for IBSC development in the face of unavoidable origin of shut resistance such as non-optical electron relaxation from the CB and thermal electron escape form the IB.