Optimum Designing of Single Crystalline Silicon Thin Film Solar Cells with Graded Active Layer

Abstract

A carrier density gradient was given to the p-doped active layer of a conventional p–n junction solar cell employing the concept of the p–i–n junction structure used in amorphous silicon solar cells. Single crystalline silicon thin film solar cells with graded carrier density in the active layer were analyzed to optimize the cell structure utilizing a two-dimensional device simulator. Two types of cell structures were designed. In the case of Cell1, the carrier density was fixed to be 1016 cm-3 on the back surface field (BSF) side and changed exponentially for the p–n junction side from 1013 cm-3 to 1018 cm-3. On the other hand, in the case of Cell2, the carrier density was fixed to be 1016 cm-3 on the p–n junction side and changed exponentially for the BSF side from 1013 cm-3 to 1018 cm-3. Improvement in short circuit current density and open circuit voltage was observed. Therefore, high efficiency was expected under an electric field, considering the carrier density gradient. In the case of a solar cell with a 5-µm-thick solar grade single crystalline silicon film, a conversion efficiency of about 14% was obtained for a flat surface solar cell.