Brief Comparison of Tandem and Cascaded Solar Cells

Current review is focused on comparison of technology, design and fabrication of hetero-structured solar cells made in different configurations and using different materials. The widely studied hetero-structured solar cells are represented by two major groups, namely, tandem, and cascaded solar cell configurations. The major element in solar cell of both groups is intrinsic region of the designed p-i-n junction, where electron – hole pairs are generated by absorbed light and, most importantly, separated one from the other. The energy gap and absorption coefficient of semiconductor used for the i-region defines the harvested part of solar spectra and efficiency of solar cell. Tandem solar cells are built as stacks of separate p-n junctions, where every junction is made of a semiconductor with preselected energy gaps Eg, absorbing different part of sun spectra. Connected in sequence with decreasing values of energy gap from top to bottom, these stacks in a tandem cell harvest different segments of sun spectra. On the contrary, cascaded solar cell consist of a set of i-regions made of semiconductors with different energy gaps built into a single p-n junction. The thickness of every i-region is designed to provide maximum absorption for preselected part of the sun spectra. In current study, we compare for both groups the ability to harvest widest part of sun spectra, efficiency, complexity of design, as well as cost of solar cell production.