Solar Cell Band Diagramconduction band(empty)negative charge(electron)1forbiddenpue snoetiepueg aa/elaoaenergy band(gap)eOFermipositiveenergycharge(hole)Valence band(fullb)metalmetaln-dopedp-dopedcontactcontactsemicondsemicond6
6 Solar Cell Band Diagram
Question2:The bandgap of GaAs is 1.4 eV. Calculate the optimumwavelength of light for photovoltaic generation in a GaAs solalcell.7
7 Question 2: The bandgap of GaAs is 1.4 eV. Calculate the optimum wavelength of light for photovoltaic generation in a GaAs solar cell
Typical Embodiment of a p-n JunctionNeutralARCLayerE.Neutral p-regionn-regionDriftDiffusionLongaShort入2Medium入LhBackelectrode.Finger electrodeW.W.In1Depletion Region0048http://electrons.wikidot.com/solar-cellsARC:anti-reflectivecoating
Typical Embodiment of a p-n Junction 8 Eo ARC Layer Neutral p-region Long λ Medium λ Short λ Depletion Region + _ + - Le Lh Voc Wp Neutral n-region Finger electrode lp ln + + - - Drift Diffusion Back electrode Wn ARC: anti-reflective coating http://electrons.wikidot.com/solar-cells
Description: Cell is illuminated through thin n-region.ARC reduces reflections from surface: Space charge / depletion region extends primarily into p-side (N.W, = NaW) - more heavily doped n-region: As usual there is a built-in electric field across thedepletion region, E。Na -concentration of acceptor atoms = p in p-type semiconductor (concentration of holes)Nd- concentration of donor atoms = n in n-type conductor (concentration of electrons)Wp-depletion width on the p sideWn - depletion width on the n side9
Description • Cell is illuminated through thin n-region • ARC reduces reflections from surface • Space charge / depletion region extends primarily into pside (NaWp = NdWn) – more heavily doped n-region • As usual there is a built-in electric field across the depletion region, Eo Na – concentration of acceptor atoms = p in p-type semiconductor (concentration of holes) Nd – concentration of donor atoms = n in n-type conductor (concentration of electrons) Wp – depletion width on the p side Wn - depletion width on the n side 9
Operation. Photons are not all absorbed / reflected from the surface -- butcan penetrate a certain depth into the material (depends onwavelength).As n-region is very thin, (typically < 0.2 μm), most of thephotons are absorbed in the depletion region and the p-regionAbsorption of a photon leads to the creation of an electron-hole-pair (EHP)Within depletion region, EHP drift apart due to the forceexerted by E.Electrons → n-side, holes p-sideThis leads to an open-circuit voltage developing across thedevice, with p-side positive the n-side negative10
Operation • Photons are not all absorbed / reflected from the surface – but can penetrate a certain depth into the material (depends on wavelength) • As n-region is very thin, (typically < 0.2 µm), most of the photons are absorbed in the depletion region and the p-region • Absorption of a photon leads to the creation of an electronhole-pair (EHP) • Within depletion region, EHP drift apart due to the force exerted by Eo. Electrons à n-side, holes à p-side • This leads to an open-circuit voltage developing across the device, with p-side positive the n-side negative 10