Multi junction solar cells using band-gap induced cascaded light absorption

Abstract

We propose multi junction solar cells using an optical reflection system formed by arranging plural solar cells in decreasing order of their band gaps for achieving cascaded light absorption by their own band gaps: the first solar cell absorbs some light with a photon energy higher than the highest band gap and reflects the residual light with a lower photon energy to the second solar cell. We further propose to use plural batteries for charging electrical power generated by the individual solar cells to overcome the current matching problem in the multi-junction solar cells. We experimentally demonstrated reflection-type multi junction solar cells using commercially available hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) solar cells using air mass 1.5 light illumination. A high open circuit voltage of 24.3 V was achieved, which was a sum of 19.3 and 5.0 V for the individual a-Si:H and c-Si solar cells. However, since there was no current matching between the a-Si:H and c-Si solar cells, the a-Si:H-c-Si serially connected solar cell gave a maximum power of 0.057 W, which was lower than 0.063 W, the sum of those for the individual a-Si:H and c-Si solar cells. The method of charging electrical power from individual solar cells is useful to efficiently achieve electrical power from individual a-Si:H and c-Si solar cells in the absence of current matching in multi junction solar cells.

Reduction in connecting resistivity and optical reflection loss at intermediate layer for mechanically stacked multijunction solar cells

“…9) Mechanically stacked multijunction solar cells have also been reported. [12][13][14][15][16][17][18][19][20][21][22] The mechanical stacking of individual solar cells allows the use of a wide selection of semiconductor materials such as amorphous, polycrystalline, organic semiconductors, and single-crystalline inorganic semiconductors. Moreover, this method makes it possible to fabricate large solar cells.…”