multijunction

Multijunction refers to an electronic or optoelectronic device that contains two or more p–n junctions within a single device. In contrast to single-junction devices, multijunction configurations stack different semiconductor materials or regions so that each junction has a different bandgap, enabling absorption of complementary portions of the spectrum. They are typically connected in series so that the same current flows through all junctions, and the total output voltage is the sum of the subcells’ voltages.

The most prominent example is the multijunction solar cell. Each subcell is engineered to harvest photons corresponding to its bandgap, reducing thermal losses and increasing the overall efficiency. Subcells are often grown on a common substrate on lattice-matched materials; when lattice mismatch is present, metamorphic or hybrid approaches using tunnel junctions may be used to connect subcells.

Design considerations include current matching between subcells, optical coupling, and electrical interconnections. Tunnel junctions or thin metal interconnects are used to connect subcells. While multijunction devices offer higher theoretical efficiency limits than single-junction counterparts, they face higher manufacturing costs, materials constraints, and reliability challenges due to lattice mismatch and thermal expansion.

Applications span space-based solar power, concentrator photovoltaics on Earth, and certain photodetector or optoelectronic systems where broad spectral response or high voltage is advantageous. Variants include two-, three-, or four-junction cells and other multi-junction optoelectronic structures. Owing to rapid advances in materials science, multijunction concepts continue to influence high-efficiency solar energy and photodetection technologies.