An alternative group of materials that give long-lived intermediate states are those based on the lanthanide (or rare-earth) group of elements, because of their narrow and suitably spaced energy transitions. The lanthanides have a valence shell of 4f electrons that are shielded by full outer 6s and 5p shells. Hence, their electronic transitions tend to […]

One such long-lived energy state can be achieved in the transfer of electrons from ‘allowed’ excited singlet states to ‘forbidden’ excited triplet states in some organic molecules (S-T transitions).[7] Exploitation of this for upconversion has been demonstrated by [Baluschev et al., 2007]. The spin-orbit coupling that can occur due to the heavy-metal atoms in some […]

An UC device is designed to absorb subbandgap photons in an UC layer behind a bifacial solar cell. This layer radiatively absorbs two or more long-wavelength photons and emits a photon of higher energy above the bandgap of the bifacial solar cell. Thus, the current in the device is boosted by photons that would not […]

An alternative approach is to absorb a short-wavelength photon high up in the conduction band of various semiconductors. There is then the possibility of an impact ionisation event (i. e. reverse Auger recombination) in which the high-energy electron excites an additional electron to the conduction band, thus creating two or more electron-hole pairs at the […]

Praseodymium (Pr3 +) is a good choice because of its widely dispersed energy levels well matched for photon cutting, [Dieke, 1968], see Figure 9.10. The 3P2, % and P0 levels at between 440 and 490 nm can absorb blue photons that can then radiatively recombine via the :G4 level at 1010 nm – at just […]

A downconverting device (DC) must be placed in front of a standard cell and can boost current by converting a UV photon to more than one photon just above the bandgap of the solar cell – thus boosting the current. However, the DC does require that more lower-energy photons are emitted than high-energy photons absorbed, […]

As an alternative to modifying the structure of a solar cell, another approach is to modify the spectrum incident on the cell to narrow its bandwidth and make it closer to optimal for a single-bandgap cell. This involves a limiting quantum efficiency (QE) of conversion of photons to electron-hole pairs in the cell not limited […]

The IBSC has an additional energy level (the intermediate band) within the bandgap of a single-junction cell such that this level absorbs photons below the bandgap energy in parallel with the normal absorption of above bandgap photons in the cell. Photons with less energy than the primary bandgap can be absorbed by transitions from the […]