Microcrystalline and Amorphous Silicon Tandem Solar Cells

For about the last 10 years, researchers have been attempting to develop ultrathin microcrystalline solar cells using far smaller crystals than those used in today’s polycrystalline and multicrystalline solar cells. However, to achieve this, light must be trapped and retained in the cell very efficiently so as to attain sufficient current density and photon absorption. Crystal miniaturization also substantially reduces open-circuit voltage Voc relative to that of crystalline solar cells. Moreover, the miniaturized lattice that is obtained with microcrystalline solar cells obviates the Staebler-Wronski effect. Efficiency amounting to zpV — 10.1% has already been achieved for small-scale lab cells 2 pm thick (AZ ~ 1.2 cm2) [Mar03], [3.2].

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Microcrystalline solar cells are very suitable for use as back cells in optically and electrically series – connected tandem arrays with an amorphous silicon front cell. This arrangement is known as a micromorph solar cell. Inasmuch as only the front cell is amorphous, the Staebler-Wronski effect is far less pronounced in the cell as a whole than is the case with pure amorphous cells. Initial efficiency amounting to zpV — 14.5% has already been achieved for small-scale lab cells (AZ~ 1cm2) [Mar03]. Figure 3.56 shows a cross-section of this type of microcrystalline and amorphous silicon tandem cell.

—– glass superstrate

—– transparent front contact

—– amorphous front cell

—– microcrystalline back cell

—– metallic back contact

Updated: August 4, 2015 — 8:27 am