Materials chemistry

OLEDs, solar cells

How organic electroluminescent diodes turn injected charge into light, and how photovoltaic devices turn absorbed photons into useful electrical work.

IntuitionFrom photons to function

An OLED is a thin stack that injects electrons and holes into an organic emitter; their recombination can release a photon. A solar cell follows the reverse energy path: a photon creates an excited state, and selective contacts separate its charges before they recombine.

SchoolThe device-level picture

In a simple OLED, the anode supplies holes and the cathode supplies electrons. Transport layers help balance injection; an emissive layer hosts excitons. The external circuit supplies energy, so light output is not spontaneous chemical energy release.

UndergraduateEnergy levels and losses

In molecular semiconductors, frontier orbitals are often described by HOMO and LUMO levels; in a solid these broaden into transport states. Exciton binding can be substantial, so donor–acceptor interfaces or high-permittivity environments may assist charge separation. Offsets that are too large waste energy.

AdvancedMaterials and device physics

For a solar cell, the open-circuit voltage is limited by the absorber band gap and by radiative and non-radiative recombination. The short-circuit current depends on the spectrum, absorption, and collection probability. A useful strategy is to diagnose the full current–voltage curve rather than equating a strong absorption spectrum with a good device.

ResearchResearch frontier