#Light Absorption in Solar Cells

Light absorption in a solar cell is not a simple on/off process. A photon arriving at the panel surface must first pass through the glass cover (which filters some UV), then the anti-reflection coating (which reduces surface reflection), then the EVA encapsulant, before reaching the silicon cell where - if its energy matches the material's requirements - it can free an electron and contribute to current.

The probability that a photon arriving at the cell surface actually generates a usable electron is captured by the external quantum efficiency (EQE) curve. For standard monocrystalline silicon, EQE peaks at roughly 85 - 90% between 600 nm and 700 nm, drops to 40 - 60% in the blue visible range, and falls to 20 - 40% across most UV wavelengths. At wavelengths above 1,100 nm, EQE drops to zero - photons at those wavelengths don't carry enough energy to cross silicon's 1.12 eV bandgap.

Photons that do have more than enough energy - UV photons, in particular - don't simply generate proportionally more electricity. The excess energy above 1.12 eV converts to heat through a process called thermalization loss, which is why single-junction silicon can't convert UV photons efficiently regardless of how many arrive. This is the fundamental physics that next-generation multi-junction and tandem cell architectures are designed to address.

Anti-reflection coatings help by reducing front-surface reflection losses across the visible range. Down-conversion phosphors (in experimental luminescent solar concentrators) attempt to shift UV photons to visible wavelengths before they hit the cell, improving overall capture efficiency for that spectral band.