Multi-junction solar cell
![Black light test of Dawn's triple-junction gallium arsenide solar cells[1]](/Images/godic/202502/15/Black_light_test_of_Dawns_solar_cells0900.jpg")
![Figure A. Band diagram illustration of the photovoltaic effect. Photons give their energy to electrons in the depletion or quasi-neutral regions. These move from the valence band to the conduction band. Depending on the location, electrons and holes are accelerated by Edrift, which gives generation photocurrent, or by Escatt, which gives scattering photocurrent.[9]](/Images/godic/202502/15/Effetphotovoltaic0900.jpg")
![The Shockley-Queisser limit for the efficiency of a single-junction solar cell. It is essentially impossible for a single-junction solar cell, under unconcentrated sunlight, to have more than ~34% efficiency. A multi-junction cell, however, can exceed that limit.](/Images/godic/202502/15/ShockleyQueisserFullCurve.svg0900.png")
![Figure C. (a) The structure of an MJ solar cell. There are six important types of layers: pn junctions, back surface field (BSF) layers, window layers, tunnel junctions, anti-reflective coating and metallic contacts. (b) Graph of spectral irradiance E vs. wavelength λ over the AM1.5 solar spectrum, together with the maximum electricity conversion efficiency for every junction as a function of the wavelength.[11]](/Images/godic/202502/15/StructureMJetspectre0900.png")
Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light. The use of multiple semiconducting materials allows the absorbance of a broader range of wavelengths, improving the cell's sunlight to electrical energy conversion efficiency.