Application

Photovoltaics

Turning light directly into electricity in a semiconductor junction — the application that made silicon a bulk commodity rather than an electronics material.

A photovoltaic cell is a semiconductor junction thin enough for light to reach it, arranged so that a photon knocking an electron loose sends it out of the cell rather than letting it fall back. Everything else is engineering around that one effect.

Which semiconductor is a live question rather than a settled one. Crystalline silicon dominates on cost and durability, and the thin-film alternatives — cadmium telluride above all — compete by using far less material per watt. The materials chosen determine the supply chain, and several elements with no other large market depend entirely on which technology wins.

Economic significance

Photovoltaics changed what silicon is. Electronics needed it very pure and in small quantity; solar needs it slightly less pure and in enormous quantity, and the second market is now far the larger.

For the thin-film elements the dependence runs the other way. Tellurium has no ore body worth mining and reaches the market only as a by-product of copper refining, so a technology built on cadmium telluride is limited by how much copper the world happens to refine — a constraint that has nothing to do with sunlight.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

uses

Silicon — element · crystalline silicon dominates, at slightly lower purity and far greater quantity than electronics needs
Cadmium — element · as cadmium telluride, the main thin-film technology competing with silicon
Tellurium — element · the other half of cadmium telluride, and the constraint on how far that technology can scale
Gallium — element · gallium arsenide gives the most efficient cells, at a cost that restricts them to space and concentrators
Indium — element · in thin-film cells, alongside its larger use as the transparent electrode
Silver — element · as the paste forming the contact grid on a silicon cell
Cadmium telluride — compound · the only thin-film technology to have taken and held real market share from silicon
Gallium arsenide — compound · in multi-junction cells for spacecraft, where efficiency per unit area is worth almost any price
Polysilicon — material · the material the whole industry rests on, and the largest single contributor to a solar panel's embodied energy
Solar panel — object · and the price fell roughly ninety-nine per cent in thirty years on thinner wafers, finer saws and rising cell efficiency

Sources

Material World
Our own writing

Questions this page answers

What is used for Photovoltaics?

Where it comes from, and what it becomes

Follow Photovoltaics back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

Photovoltaics → uses (crystalline silicon dominates, at slightly lower purity and far greater quantity than electronics needs) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation → takes as input (the feedstock, and an unusual one in being free, unlimited and available anywhere — the cost is entirely the energy to liquefy it) → Air
Photovoltaics → uses (as the paste forming the contact grid on a silicon cell) → Silver → is sourced from (from the anode slimes of copper electrorefining, the same stream the platinum group and the tellurium come out of) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
Photovoltaics → uses (gallium arsenide gives the most efficient cells, at a cost that restricts them to space and concentrators) → Gallium → is sourced from (as a by-product of the Bayer process) → Bauxite → is sourced from (the residue of prolonged tropical weathering, which strips the silica and alkalis out of an aluminosilicate rock and leaves the aluminium behind — basalt is one common parent among several) → Basalt → is sourced from (partial melting of mantle peridotite is what basalt magma is — the residue left behind stays peridotite, depleted of what went into the melt) → Peridotite → is composed of (the mineral that defines the rock and gives it its name — a peridotite is olivine-dominant by definition) → Olivine
Photovoltaics → uses (the other half of cadmium telluride, and the constraint on how far that technology can scale) → Tellurium → is sourced from (recovered from copper refining anode slimes) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
Photovoltaics → uses (in multi-junction cells for spacecraft, where efficiency per unit area is worth almost any price) → Gallium arsenide → is produced by (grown as a boule and sliced, though it is harder to keep stoichiometric than silicon because the arsenic evaporates) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
Photovoltaics → uses (the material the whole industry rests on, and the largest single contributor to a solar panel's embodied energy) → Polysilicon → is sourced from (metallurgical-grade silicon at 98 or 99 per cent, which is fine for alloying and useless for anything electronic — the purification from there is the entire product) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation

These are the most distinct paths back. Photovoltaics can be traced through others besides.