Efficient Intraband Photoexcitation in Two-step Photon Up-Conversion Solar Cells Using Double-Tunnel Junction

Recently, we proposed an innovative structure for solar cells that theoretically surpasses the efficiency limit of single-junction solar cells. These are referred to as two-step photon up-conversion solar cells (TPU-SCs). To date, we have demonstrated a significant increase in photocurrent resulting from intraband transitions at the heterointerface of different semiconductors that make up the solar cell. However, this photocurrent enhancement has not yet reached a level sufficient to achieve high conversion efficiency. Last year, we introduced an additional structure designed to enhance intraband absorption, termed a double-tunnel junction. This structure is expected to suppress carrier recombination at the heterointerface and prevent the back diffusion of intraband-excited carriers. In this study, we present experimental results that demonstrate a more pronounced photocurrent enhancement due to intraband absorption enabled by incorporating the double-tunnel junction.