SOL 102 › Glossary

SOL 102 glossary

Every technical term and abbreviation used in SOL 102, in plain language: 313 entries. Each links to the page where it is first explained.

Columns: the term or abbreviation; its full name (for abbreviations) or symbol and unit; a plain-language definition; and where it is introduced. "—" means the term is not an abbreviation.

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Term	Full name / symbol	Plain definition	Introduced
Absorber	—	The material layer in a solar cell that absorbs sunlight and generates charge carriers.	Unit 1
Acid etch	—	Hydrofluoric–nitric acid mix (HF/HNO₃) that etches silicon isotropically.	Unit 8
Activation energy	E_a	The energy barrier a process must overcome.	Unit 7
Adatoms	—	Atoms adsorbed on and moving across a surface.	Unit 9
ALD	atomic layer deposition	Building a film one atomic layer per cycle using alternating self-limiting precursor pulses.	Unit 9
Alkaline etch / texture	—	Potassium hydroxide (KOH) or sodium hydroxide (NaOH) solution that etches silicon anisotropically, forming pyramids.	Unit 8
Amorphous	—	Lacking long-range order (no repeating lattice) but with short-range order of nearest neighbours.	Unit 4
Anisotropic / isotropic etch	—	Anisotropic etches at different rates in different crystal directions; isotropic etches equally in all directions.	Unit 8
Anisotropy	—	Properties that differ with direction in a crystal (etch rate, cleavage, strength).	Unit 3
Anneal	—	Heating to let atoms rearrange, relieve stress or activate dopants.	Unit 7
ARC	anti-reflection coating	A thin film whose thickness and refractive index cancel reflections by interference.	Unit 9
Arrhenius law	D = D₀ exp(−E_a/kT)	Diffusion (and many rates) rise exponentially with temperature; D₀ is pre-exponential factor, E_a activation energy (eV).	Unit 7
a-Si	amorphous silicon	Disordered silicon; hydrogenated (a-Si:H) layers passivate surfaces in heterojunction cells.	Unit 4
Asphyxiant	—	A gas that displaces oxygen.	Unit 11
Atom	—	The smallest unit of a chemical element: a tiny dense nucleus surrounded by electrons.	Unit 1
Atomic number	Z	The number of protons in an atom's nucleus (silicon: 14).	Unit 1
Atomic radius	—	The approximate size of an atom; it grows down a group and shrinks across a period.	Unit 1
Avogadro's number	N_A ≈ 6.022 × 10²³ per mole	The number of particles in one mole.	Unit 1
Backsheet	—	The polymer laminate on a module's rear for insulation and moisture protection.	Unit 10
Band gap	E_g	The energy range with no allowed electron states between the valence and conduction bands; silicon's is 1.12 eV at room temperature.	Unit 1
Band-gap engineering	—	Choosing or mixing materials to obtain a desired band gap.	Unit 2
Basis	—	The atom or group of atoms attached to each lattice point.	Unit 3
Bill of materials	BOM	List of components and materials in a product.	Unit 10
Binary phase diagram	—	A phase diagram for a two-element system.	Unit 6
B–O defect	boron–oxygen defect	A complex that forms under light in boron-doped, oxygen-rich silicon and causes LID.	Unit 5
Body diagonal	—	The line through a cube from one corner to the opposite corner.	Unit 3
Boltzmann's constant	k = 8.617 × 10⁻⁵ eV/K	Links temperature to typical thermal energy; kT ≈ 0.0259 eV at 300 K.	Unit 5
Bonding / antibonding states	—	Combining two atomic orbitals gives a lower-energy bonding state (electrons hold atoms together) and a higher-energy antibonding state.	Unit 2
Bragg's law	nλ = 2d sin θ	Condition for strong X-ray reflection: path difference between planes spacing d equals a whole number n of wavelengths λ; θ is the angle to the planes.	Unit 3
Brittle / ductile	—	Brittle materials crack without bending (silicon, glass); ductile materials bend and stretch first (copper, silver).	Unit 2
BSF	back-surface field	A heavily doped (p⁺) layer at the rear that repels minority carriers; aluminium–silicon alloying forms it.	Unit 6
Busbars / fingers	—	Fingers are thin printed lines collecting current; busbars are wider lines carrying it to ribbons.	Unit 10
Bypass diode	—	A diode in the junction box that routes current around shaded cell groups.	Unit 10
Calcium gluconate gel	—	First-aid gel for HF skin exposure that binds fluoride.	Unit 11
Capture cross-section	σ; cm²	The effective target area a defect presents to a passing carrier.	Unit 5
Carbothermic reduction	—	Making silicon by reacting quartz with carbon at about 2000 °C: SiO₂ + 2C → Si + 2CO.	Unit 8
Cation / anion	—	A cation is a positive ion; an anion is a negative ion.	Unit 3
Caustic	—	Strongly alkaline and corrosive (e.g. potassium hydroxide).	Unit 11
Ceiling limit	—	A concentration never to be exceeded, even briefly.	Unit 11
Chalcopyrite	—	A doubled zinc-blende-type structure with two cation types, e.g. copper indium gallium selenide (CIGS).	Unit 3
Charge carriers	—	Mobile particles that carry current: electrons in the conduction band and holes in the valence band.	Unit 2
Chemical passivation	—	Tying up dangling bonds (e.g. with hydrogen) to remove trap states.	Unit 2
Cleanroom	—	A room with filtered air and controlled practices limiting particles and contamination.	Unit 5
Cleaving / cleavage	—	Breaking a crystal along its weakest planes; silicon cleaves most easily on {111}.	Unit 3
Complementary error function	erfc	The S-shaped function giving the profile from a constant surface source.	Unit 7
Concentration gradient	dC/dx	How steeply concentration changes with depth.	Unit 7
Conduction band	—	The band of higher energy states where electrons move freely and carry current.	Unit 2
Conductor / insulator	—	A conductor carries current easily (metals); an insulator barely at all (glass, plastics).	Unit 2
Conformal	—	Coating evenly over all surfaces, including steep sides.	Unit 9
Coordination number	—	Number of nearest neighbours of an atom (silicon: 4).	Unit 12
Corrosive	—	Destroys skin or materials on contact.	Unit 11
Coulomb	C	The SI unit of electric charge; about 6.24 × 10¹⁸ electrons' worth.	Unit 1
Covalent bond	—	A bond in which two atoms share a pair of electrons; silicon's bonds are covalent.	Unit 2
Cross-linking	—	Chemical bonds joining polymer chains into a network.	Unit 10
Crucible	—	The container (quartz for Cz silicon) holding molten material.	Unit 5
Crystal	—	A solid whose atoms repeat in a regular pattern in all three directions.	Unit 3
Crystal habit	—	The characteristic outer shape a crystal grows into.	Lab A
CSS	close-spaced sublimation	Depositing films (e.g. cadmium telluride) by subliming a source held close to the substrate.	Unit 9
CTE	coefficient of thermal expansion	Fractional length change per degree (ppm/K); silicon ≈ 2.6, copper ≈ 17.	Unit 10
Current	I; unit ampere (amp, A)	The rate at which charge flows past a point: one amp is one coulomb per second.	Unit 1
CVD	chemical vapour deposition	Forming a solid film from gases reacting on a heated surface.	Unit 8
Cz	Czochralski process	Growing a single-crystal ingot by slowly pulling a rotating seed crystal from molten silicon.	Unit 3
Damp heat	—	Test at 85 °C and 85 % relative humidity, typically 1000 h.	Unit 10
Dangling bonds	—	Unpaired electrons at surfaces or defects where a neighbour atom is missing; they trap carriers.	Unit 2
Deal–Grove model	—	Oxide growth model: linear rate when thin, parabolic (√time) when thick.	Unit 8
Deep levels	—	Defect energy levels near mid-gap; efficient recombination centres.	Unit 5
Delamination	—	Separation of a film or layer from what it was bonded to.	Unit 9
Density	ρ; g/cm³	Mass per unit volume (silicon: 2.329 g/cm³).	Unit 1
Diamond cubic	—	Silicon's crystal structure: two interpenetrating face-centred cubic lattices offset by a quarter body diagonal; 8 atoms per cell.	Unit 3
Diamond-wire sawing	—	Slicing ingots with a thin steel wire coated with diamond grit.	Unit 4
Diffractometer	—	The instrument used for X-ray diffraction.	Unit 3
Diffusion	—	Net spreading of atoms from high to low concentration by random thermal motion.	Unit 7
Diffusion coefficient	D; cm²/s	How fast particles spread by random motion.	Unit 4
Diffusion length	L = √(Dτ)	Average distance a minority carrier wanders before recombining; D is diffusion coefficient (cm²/s), τ lifetime (s).	Unit 4
Dipole	—	A pair of separated positive and negative charges.	Unit 2
Directional bond	—	A bond that points in a fixed direction, giving rigid, brittle crystals.	Unit 2
Directional solidification	—	Freezing a melt from one end so impurities with k₀ < 1 concentrate in the last-to-freeze part.	Unit 6
Dislocation (edge, screw)	—	A line defect where the lattice is misaligned; edge and screw are the two basic types.	Unit 5
DI water	deionised water	Water with ions removed, used for rinsing.	Unit 11
Dopants	—	Impurity atoms deliberately added in tiny amounts to control a semiconductor's conductivity.	Unit 1
Dose	Q; atoms/cm²	Total dopant per unit surface area.	Unit 7
EC	electrical conductivity	How easily a solution conducts current; measured in microsiemens per centimetre (µS/cm), rising with dissolved salt.	Lab D
Edge isolation	—	Removing the conducting doped layer at wafer edges so front and back are not shorted.	Unit 8
Effective segregation coefficient	k_eff	The measured segregation ratio in a real (not perfectly mixed) freezing process; closer to 1 than k₀.	Lab D
Electric charge	—	A basic property of particles that makes them push or pull on each other; positive and negative charges attract, like charges repel.	Unit 1
Electron	—	A light, negatively charged particle around the nucleus; electrons carry electric current in metals and semiconductors.	Unit 1
Electron configuration	—	The list of which orbitals an atom's electrons occupy, e.g. silicon 1s² 2s² 2p⁶ 3s² 3p².	Unit 1
Electronegativity	—	How strongly an atom pulls shared bonding electrons toward itself (Pauling scale).	Unit 1
Electronegativity difference	Δχ	Difference in electronegativity between two bonded atoms; larger means more ionic.	Unit 2
Electron-volt	eV	The energy one electron gains moving through 1 volt: 1.602 × 10⁻¹⁹ J. The natural energy unit for atoms and band gaps.	Unit 1
Elementary charge	e (≈ 1.602 × 10⁻¹⁹ C)	The charge of one proton (positive) or one electron (negative); the smallest free unit of charge.	Unit 1
Ellipsometry	—	Measuring film thickness and refractive index from changes in light polarisation on reflection.	Unit 9
Emitter	—	The thin heavily doped surface layer of a cell forming the junction with the base.	Unit 7
Encapsulant	—	The polymer that bonds and protects the cells inside a module.	Unit 10
Enthalpy	H; J or J/mol	Heat content of a system.	Unit 6
Entropy	S; J/K	A measure of disorder or the number of possible arrangements.	Unit 6
EPE	EVA–POE–EVA	A co-extruded encapsulant sandwich combining both materials.	Unit 10
Epitaxy	—	Growing a crystalline film that continues the crystal structure of the substrate below.	Unit 3
Equilibrium	—	The state a system settles into given enough time, with no net change.	Unit 6
Eutectic point	—	The lowest-melting composition of a binary system, where liquid freezes directly into two solids (Al–Si: 577 °C, 12.6 wt% Si).	Unit 6
EVA	ethylene-vinyl acetate	The most common encapsulant; cross-linked during lamination; can release acetic acid.	Unit 10
Evaporation	—	Heating source material in vacuum so its vapour condenses on the substrate.	Unit 9
Excess-flow valve	—	Valve that shuts if flow exceeds a set limit, as in a line break.	Unit 11
Facets	—	Flat crystal faces.	Lab A
Fatigue	—	Cracking from repeated cycles of stress.	Unit 10
FBR	fluidised-bed reactor	A reactor where silane decomposes on silicon seed granules suspended by gas.	Unit 8
FCC	face-centred cubic	A cubic lattice with atoms at the corners and the centre of each face.	Unit 3
Fick's first law	J = −D dC/dx	Flux J (atoms per cm² per s) is proportional to the concentration gradient dC/dx.	Unit 7
Fick's second law	∂C/∂t = D ∂²C/∂x²	How concentration C changes with time t from the curvature of the profile.	Unit 7
Field-effect passivation	—	Using fixed charge in a coating to repel one carrier type from the surface so recombination slows.	Unit 2
Firing	—	A brief high-temperature heat spike (peak roughly 700–800 °C) that sinters metal paste and forms contacts.	Unit 2
Flammable range	—	The fuel–air concentrations between which a gas can burn.	Unit 11
Flats / notches	—	Edge features ground on wafers (mainly for microelectronics) to mark crystal orientation.	Unit 3
Flux	J	Amount crossing unit area per unit time.	Unit 7
FMEA	failure mode and effects analysis	Systematic review of how things can fail and the consequences.	Unit 11
Four-point probe	—	Instrument with four in-line pins: current through the outer two, voltage on the inner two, giving resistivity or sheet resistance.	Unit 5
Fractional distillation	—	Separating liquids by boiling points.	Unit 8
Gas cabinet	—	Exhausted enclosure for gas cylinders with automatic shut-off.	Unit 11
Gaussian profile	—	The bell-shaped profile from a fixed dose (limited source) driven inward.	Unit 7
Gettering	—	Drawing harmful impurities out of the active region into sacrificial zones (e.g. heavily doped surface layers).	Unit 5
Gibbs free energy	G = H − TS	The energy quantity minimised at equilibrium at fixed temperature and pressure; H is enthalpy, T temperature (K), S entropy.	Unit 6
Glass frit	—	Powdered glass in silver paste that etches through the antireflection coating during firing.	Unit 6
Glass-transition temperature	T_g	The temperature at which an amorphous polymer changes from rigid/glassy to soft/rubbery.	Unit 2
Goldschmidt tolerance factor	t	A ratio of ionic radii predicting whether a perovskite structure is stable (roughly 0.8–1.0).	Unit 3
Gowning	—	Putting on cleanroom garments.	Unit 11
Grains / grain boundaries	—	Grains are individual crystals in a polycrystalline solid; grain boundaries are the disordered interfaces between them.	Unit 4
Groups / periods	—	Groups are the table's columns (similar chemistry); periods are its rows (same outermost shell).	Unit 1
Growth modes	—	Layer-by-layer, island, or layer-then-island film growth.	Unit 9
Halides	—	Compounds of the halogens (fluorine, chlorine, bromine, iodine).	Unit 3
HF	hydrofluoric acid	Acid that dissolves silicon dioxide; extremely hazardous to skin and body.	Unit 8
Hierarchy of controls	—	Elimination, substitution, engineering controls, administrative controls, then PPE (least effective).	Unit 11
HJT	heterojunction technology	A cell design with thin amorphous-silicon layers on a crystalline wafer, processed below ~250 °C.	Unit 4
Hole	—	A missing electron in a bond; it moves through the crystal and behaves like a positive charge carrier.	Unit 1
Humidity-freeze	—	Test combining humid heat and sub-zero cycling.	Unit 10
Hydrogen bond	—	A moderately strong attraction between a hydrogen atom bonded to O, N or F and a neighbouring electronegative atom.	Unit 2
Hydrolysis	—	Chemical breakdown by reaction with water.	Unit 10
Hydrophobic / hydrophilic	—	Water-repelling / water-attracting surfaces.	Unit 8
Hypocalcaemia	—	Dangerously low blood calcium, a key HF hazard.	Unit 11
IDLH	Immediately Dangerous to Life or Health	Concentration that could kill or prevent escape within 30 minutes.	Unit 11
Inclusions	—	Trapped pockets of liquid or foreign material inside a crystal.	Lab A
Inert	—	Chemically unreactive, like the noble gases (helium, argon).	Unit 1
Ingot	—	A large solid block or cylinder of crystal grown from molten silicon, later sliced into wafers.	Unit 1
Interface states	—	Allowed energy levels inside the band gap created at boundaries or surfaces.	Unit 4
Interstitial	—	An atom squeezed between normal lattice sites.	Unit 5
Intrinsic carrier density	n_i ≈ 10¹⁰ cm⁻³ at 300 K	The number of electrons (and holes) in undoped silicon from heat alone.	Unit 5
Intrinsic stress	—	Built-in stress of a film from how it grew.	Unit 9
Ion	—	An atom that has gained or lost electrons and so carries a net charge.	Unit 1
Ion cores	—	Atoms minus their outer electrons, in a metal.	Unit 2
Ionic bond	—	A bond formed when one atom transfers electrons to another and the resulting ions attract electrostatically.	Unit 2
Ionic radii	—	Effective sizes of ions in a crystal.	Unit 3
Ionisation energy	—	The energy needed to remove an electron from an atom.	Unit 1
Isotopes	—	Atoms of the same element with different numbers of neutrons (e.g. silicon-28, -29, -30).	Unit 1
Joule	J	The SI unit of energy.	Unit 1
Junction box	—	The rear box holding the module's electrical connections and bypass diodes.	Unit 10
Junction depth	x_j	Depth where diffused dopant equals background doping, forming the p–n junction.	Unit 7
Jupyter notebook	—	A browser-based document where code runs in cells with output shown below.	Unit 12
Kerf	—	Material lost as sawdust when a saw cuts a wafer.	Unit 1
kJ/mol	kilojoules per mole	Energy per mole of bonds; divide by 96.5 to get eV per bond.	Unit 2
Lamination	—	Heating and pressing the module stack in vacuum so the encapsulant melts and bonds.	Unit 10
Latent heat of fusion	—	Heat released on freezing or absorbed on melting with no temperature change (silicon ≈ 1.8 kJ/g).	Unit 6
Lattice	—	The regular, repeating 3-D arrangement of atoms in a crystal.	Unit 2
Lattice constant	a	Edge length of the cubic unit cell (silicon: 5.431 Å).	Unit 3
Lattice mismatch	—	Difference in lattice constants between film and substrate.	Unit 9
Lever rule	—	Fraction of each phase from tie-line lengths: f_solid = (C₀ − C_L)/(C_S − C_L).	Unit 6
Library	—	A package of ready-made code; NumPy (arrays of numbers) and Matplotlib (plots) are used here.	Unit 12
LID	light-induced degradation	Efficiency loss in the first hours of illumination, mainly from boron–oxygen defects in p-type Cz silicon.	Unit 4
Lifetime	τ	The average time a light-generated carrier survives before recombining.	Unit 2
Liquidus / solidus	—	Above the liquidus the alloy is fully liquid; below the solidus fully solid.	Unit 6
Lockout/tagout	—	Isolating and locking energy sources before maintenance.	Unit 11
Low injection	—	Condition where light-generated carriers are far fewer than dopant-supplied carriers.	Unit 5
Low-iron glass	—	Soda-lime glass with little iron, transmitting ~91 % of light.	Unit 10
LPCVD	low-pressure chemical vapour deposition	CVD at reduced pressure for uniform films; used for TOPCon polysilicon.	Unit 9
Mass balance	—	Accounting check that total material in equals total out.	Lab D
Mean free path	λ	Average distance a gas molecule travels between collisions.	Unit 9
Mean-square displacement	⟨x²⟩ = 2Dt (1-D)	Average squared distance moved after time t.	Unit 7
Metallic bond	—	Bonding in which outer electrons are shared by all atoms as a mobile "sea" around fixed ion cores; it makes metals conductive and ductile.	Unit 2
Metallization	—	Printing and firing metal contacts (fingers and busbars) on a cell.	Unit 2
Metrology	—	The science and practice of measurement in manufacturing.	Unit 3
MG-Si	metallurgical-grade silicon	About 98–99 % pure silicon from carbothermic reduction.	Unit 8
Mid-gap	—	The middle of the band gap.	Unit 5
Miller indices	(hkl), [hkl]	Three integers naming a crystal plane (parentheses) or direction (square brackets), from the reciprocals of where a plane cuts the axes.	Unit 3
Minority carriers	—	The less numerous carrier type: electrons in p-type, holes in n-type. Their survival sets cell performance.	Unit 4
Mobility	μ; cm²/(V·s)	How fast carriers drift per unit electric field; about 1350 (electrons) and 480 (holes) in pure silicon, lower when doped.	Unit 5
Module stack	—	Layers of a module: glass, encapsulant, cells, encapsulant, backsheet or rear glass.	Unit 10
Molar mass	M; g/mol	The mass of one mole of a substance (silicon: 28.09 g/mol).	Unit 1
Mole	mol	An amount of substance containing Avogadro's number of particles.	Unit 1
Native oxide	—	The 1–2 nm silicon dioxide layer that forms on silicon in air at room temperature.	Unit 2
Neutron	—	An uncharged particle in the nucleus, with nearly the same mass as a proton.	Unit 1
Ångström	Å	10⁻¹⁰ metre (0.1 nanometre), a convenient size for atoms.	Unit 3
n-type	negative-type	Silicon doped with atoms that have five valence electrons (e.g. phosphorus), giving extra free electrons.	Unit 1
Nucleation	—	Formation of the first tiny stable clusters of a new phase.	Unit 9
Nucleus	—	The atom's central core of protons and neutrons, holding almost all its mass.	Unit 1
Octahedron	—	An eight-faced shape; in perovskites, six X anions surround each B cation.	Unit 3
Oxidiser	—	A substance that supplies oxygen or accepts electrons, intensifying fires.	Unit 11
Pascal / torr	Pa; torr	Pressure units: 1 atmosphere = 101 325 Pa = 760 torr.	Unit 9
Passivation	—	Treating a surface or defect so it stops capturing (recombining) charge carriers.	Unit 1
PECVD	plasma-enhanced chemical vapour deposition	CVD using a plasma so films grow at lower temperature (≈ 400 °C); used for silicon nitride.	Unit 9
PEL	Permissible Exposure Limit	Legally enforceable US limit set by the Occupational Safety and Health Administration (OSHA).	Unit 11
Periodic table	—	The table of elements ordered by atomic number, arranged so elements with similar outer electrons fall in the same column.	Unit 1
Perovskite	ABX₃	A crystal structure where a large cation A sits among corner-sharing BX₆ octahedra; also the name for solar absorbers like methylammonium lead iodide.	Unit 3
Phase	—	A region of material with uniform structure and composition (e.g. liquid, a crystal structure).	Unit 3
Phase diagram	—	A map of which phases are stable at each temperature and composition.	Unit 6
PID	potential-induced degradation	Power loss from high system voltage driving ions (e.g. sodium) toward cells.	Unit 10
Pitch	—	Spacing between repeating features (e.g. fingers).	Lab B
Plasma	—	A gas partly ionised into electrons, ions and radicals.	Unit 9
POE	polyolefin elastomer	An encapsulant with low moisture uptake and high electrical resistivity, resisting PID.	Unit 10
Point defects	—	Defects at a single atomic site: vacancies, interstitials, substitutional impurities.	Unit 5
Point-of-use abatement / scrubber	—	Equipment at the tool exhaust that burns or washes out hazardous gases.	Unit 11
Poisson's ratio	ν	Sideways shrinkage per unit stretch.	Unit 9
Polar covalent bond	—	A covalent bond in which the electrons are shared unequally because the atoms differ in electronegativity.	Unit 2
Polycrystalline	—	Made of many small crystals (grains) of differing orientations.	Unit 4
Polymers	—	Long chain molecules built from repeating units (monomers); plastics and encapsulants.	Unit 2
Polysilicon	poly-Si (feedstock)	Ultra-pure silicon in chunk or granule form made from chemical refining; the raw material melted to grow ingots.	Unit 1
ppba	part per billion atomic	One impurity atom per billion host atoms; in silicon ≈ 5 × 10¹³ atoms/cm³.	Unit 1
PPE	personal protective equipment	Gloves, goggles, face shields, aprons and respirators.	Unit 11
ppm	parts per million	In air: volumes of gas per million volumes of air.	Unit 11
ppma	part per million atomic	One impurity atom per million host atoms; in silicon 1 ppma ≈ 5 × 10¹⁶ atoms/cm³.	Unit 1
Precipitates	—	Small particles of a second phase that form inside a crystal.	Unit 5
Precursor	—	The gas or chemical supplying atoms for a deposited film.	Unit 9
Pre-deposition / drive-in	—	Two diffusion steps: introduce dopant at the surface, then heat to push it deeper.	Unit 7
Proton	—	A positively charged particle in the nucleus; the number of protons defines the element.	Unit 1
PSG	phosphosilicate glass	Phosphorus-rich glass layer left after phosphorus diffusion; removed with HF.	Unit 8
p-type	positive-type	Silicon doped with atoms that have three valence electrons (e.g. boron), giving holes.	Unit 1
Purity grades / "nines"	—	Purity expressed by the count of 9s, e.g. 9N = 99.9999999 %; solar polysilicon is typically 9N or better.	Unit 1
PVD	physical vapour deposition	Depositing films by physically vaporising material (evaporation or sputtering).	Unit 9
Pyrophoric	—	Ignites spontaneously in air (e.g. silane).	Unit 11
Python	—	A free, widely used programming language.	Unit 12
Quantum mechanics	—	The physics of very small things, in which energy comes in fixed amounts and particles behave partly like waves.	Unit 1
Quarter-wave thickness	d = λ/(4n)	Film thickness for minimum reflection at wavelength λ.	Unit 9
Quenching	—	Cooling very rapidly so equilibrium is not reached.	Unit 6
Random walk	—	Motion made of many steps in random directions; the typical distance grows as √(number of steps).	Unit 7
RCA clean	(named after Radio Corporation of America)	Standard wet-cleaning sequence removing organics and metals from silicon.	Unit 8
Recombination	—	An electron falling back into a hole, so the pair's energy is lost as heat or light rather than collected.	Unit 2
Recombination centres	—	Defects that capture electrons and holes so they recombine.	Unit 4
Reducing agent	—	A substance that removes oxygen from (donates electrons to) another.	Unit 8
Refractive index	n	Speed of light in vacuum ÷ speed in the material.	Unit 9
REL	Recommended Exposure Limit	Advisory limit from the US National Institute for Occupational Safety and Health (NIOSH).	Unit 11
Resistance	R; unit ohm (Ω)	How strongly an object opposes current; R = V/I.	Unit 2
Resistivity	ρ; Ω·cm	A material's intrinsic resistance, independent of its shape: R = ρ × length / area.	Unit 2
Scheil equation	C_S = k₀C₀(1 − f_s)^(k₀−1)	Concentration in the solid when fraction f_s of a melt has frozen, for C₀ initial melt concentration.	Unit 6
Scribe	—	To scratch a line that guides a cleave.	Unit 3
SDS	Safety Data Sheet	Standard 16-section hazard document for every chemical.	Unit 11
Seed crystal	—	A small single crystal whose orientation the growing ingot copies.	Unit 3
Segregate / decorate	—	Impurities collecting at boundaries or defects ("decorating" them), often making them more harmful.	Unit 4
Segregation coefficient	k₀ = C_S/C_L	Ratio of impurity concentration in the solid to that in the liquid at the freezing interface.	Unit 6
Semiconductor	—	A material whose conductivity lies between metals and insulators and can be tuned by doping, light or temperature.	Unit 1
Shallow donor / acceptor	—	Dopant levels very close to the conduction band (donor) or valence band (acceptor), easily ionised at room temperature.	Unit 5
Sheet resistance	R_sh; ohms per square (Ω/□)	Resistance of a thin layer per square of area; = resistivity ÷ thickness.	Unit 7
Shells	—	Groups of allowed electron energy levels around a nucleus, numbered 1, 2, 3…	Unit 1
Siemens process	—	Depositing polysilicon on heated rods from trichlorosilane and hydrogen gas (CVD).	Unit 8
Silane	SiH₄	Pyrophoric gas used in PECVD.	Unit 11
Silane coupling agents	—	Molecules that bond chemically to glass at one end and to a polymer at the other, improving adhesion.	Unit 2
Silica	silicon dioxide, SiO₂	The compound of silicon and oxygen; quartz and most sand.	Unit 1
Silicates	—	Minerals built from silicon–oxygen units combined with metals; most of Earth's crust.	Unit 1
Silver paste	—	Silver powder with glass frit and organic binder, printed and fired into contacts.	Unit 10
Single crystal	monocrystalline	A solid whose lattice is continuous with one orientation throughout.	Unit 4
SOP	standard operating procedure	Written step-by-step instructions for a task.	Unit 11
Specific heat capacity	c; J/(g·K)	Energy needed to raise 1 g by 1 K.	Unit 6
sp³ hybrid	—	Four equivalent orbitals formed by mixing one s and three p orbitals, pointing to the corners of a tetrahedron.	Unit 2
Sputtering	—	Knocking atoms off a target with energetic plasma ions to coat a substrate.	Unit 9
SRH recombination	Shockley–Read–Hall recombination	Recombination through defect levels in the band gap; τ ≈ 1/(σ·v_th·N_t).	Unit 5
Strain	—	Fractional change in length.	Unit 10
Stringing	—	Soldering or bonding ribbons to connect cells into strings.	Unit 2
Structure factor	—	The sum of waves scattered by atoms in a unit cell; zero means a reflection is missing.	Unit 12
Submerged-arc furnace	—	Furnace in which electric arcs from carbon electrodes heat the charge.	Unit 8
Subshells / orbitals	s, p, d, f	Divisions of a shell; an orbital is a region where an electron is likely to be found, holding at most two electrons.	Unit 1
Substitutional	—	An impurity atom occupying a normal lattice site in place of a host atom.	Unit 5
Substrate	—	The surface on which a film is deposited.	Unit 9
Supercell	—	Several unit cells copied together into a larger block.	Unit 12
Supersaturation	—	Holding more dissolved material than equilibrium allows; drives nucleation and crystal growth.	Lab A
Surface energy	—	Energy cost of creating surface area.	Unit 9
Tandem / multi-junction cell	—	A cell stacking absorbers with different band gaps so each uses part of the spectrum.	Unit 3
TCS	trichlorosilane, SiHCl₃	Volatile liquid made from MG-Si and hydrogen chloride; distilled and decomposed to make polysilicon.	Unit 8
TDS	total dissolved solids	A meter scale converting conductivity into estimated ppm (milligrams of salt per litre) of dissolved salt.	Lab D
Tetragonal	—	A crystal shape like a cube stretched along one axis.	Unit 3
Tetrahedron	—	A four-faced pyramid; silicon's four bonds point to its corners, 109.47° apart.	Unit 2
Texture (pyramids)	—	Microscopic pyramids, typically a few µm, etched on (100) wafers to trap light; sides are {111} planes at 54.74°.	Unit 3
Thermal budget	—	The total time-at-temperature a structure can tolerate (or has received) during processing.	Unit 4
Thermal cycling	—	Accelerated test of repeated −40 to +85 °C swings.	Unit 10
Thermal donors	—	Oxygen clusters formed around 350–500 °C that act as donors and shift resistivity.	Unit 5
Thermally tempered glass	—	Glass heated and quenched so its surface is in compression, making it much stronger.	Unit 10
Thermal oxidation	—	Growing silicon dioxide by heating silicon in oxygen or steam.	Unit 8
Thermal velocity	v_th ≈ 10⁷ cm/s	The average speed of carriers due to heat.	Unit 5
Thin film	—	A layer from about a nanometre to a few micrometres thick deposited on a substrate.	Unit 9
Tie line	—	Horizontal line across a two-phase region linking the compositions of the coexisting phases.	Unit 6
TLV	Threshold Limit Value	Guideline from the American Conference of Governmental Industrial Hygienists (ACGIH).	Unit 11
Tracer	—	A substance added to make movement visible; in lab D, food dye that (like salt) tends to be rejected by growing ice.	Lab D
Transition metals	—	Elements like iron, chromium, nickel and copper; trace amounts kill carrier lifetime.	Unit 5
Trap density	N_t; cm⁻³	Number of defect traps per cubic centimetre.	Unit 5
Tunnel oxide	—	An oxide of about 1.5 nm that carriers can pass through by quantum tunnelling (used in TOPCon).	Unit 8
TWA	time-weighted average	Average exposure over a work shift (usually 8 h).	Unit 11
Twinning	—	Two crystal regions joined in mirror-image orientation.	Lab A
Two-phase region	—	Area of a phase diagram where liquid and solid (or two solids) coexist.	Unit 6
UMG silicon	upgraded metallurgical-grade silicon	Silicon purified by metallurgical rather than chemical routes; cheaper, less pure.	Unit 6
Unified atomic mass unit	u	One twelfth of the mass of a carbon-12 atom, about 1.66 × 10⁻²⁷ kg.	Unit 1
Unit cell	—	The smallest repeating box of a crystal; stacking it fills space.	Unit 3
Vacancy	—	A missing atom at a lattice site.	Unit 5
Vacancy formation energy	E_f ≈ 3–4 eV in silicon	Energy needed to create one vacancy (uncertain in the literature).	Unit 12
Valence band	—	The band of energy states filled by bonding electrons.	Unit 2
Valence electrons	—	The electrons in the outermost shell, which take part in bonding; silicon has four.	Unit 1
Van der Waals forces	—	Weak attractions between molecules from fluctuating dipoles.	Unit 2
Viscous flow	—	The resistance of a liquid to flowing; for water it falls as temperature rises, with an activation energy similar to dye diffusion in lab C.	Lab C
Voltage	V; unit volt (V)	The energy each unit of charge gains or loses between two points: one volt is one joule per coulomb. It is the "push" that drives current.	Unit 1
Wafer	—	A thin slice (about 0.13–0.18 mm today) cut from a silicon crystal; the starting piece for a solar cell.	Unit 1
Wafer bow	—	Curvature of a wafer from film stress or uneven heating.	Unit 9
Watt-peak	Wp	A module's rated power output in watts under standard test conditions (1000 W/m² sunlight, 25 °C cell).	Unit 1
wt%	weight percent	Concentration as percent by mass.	Unit 6
XRD	X-ray diffraction	Measuring crystal plane spacings from the angles at which X-rays reflect strongly.	Unit 3
Yield	—	The fraction of product that meets specification (or, in mechanics, the onset of permanent deformation).	Unit 4
Yield stress	—	The stress at which a material starts to deform permanently.	Unit 5
Young's modulus	E; Pa	Stiffness: stress ÷ strain in elastic deformation.	Unit 9
Zinc blende	—	Diamond-like structure with two different atom types alternating, e.g. gallium arsenide (GaAs), cadmium telluride (CdTe).	Unit 3
Zone refining	—	Repeatedly sweeping a narrow molten zone along a bar to push impurities to one end.	Unit 6