[1] Luque and Marti first derived a theoretical limit for an IB device with one midgap energy level using detailed balance.
[2] Green and Brown expanded upon these results by deriving the theoretical efficiency limit for a device with infinite IBs.
The first method is to introduce small, homogeneous quantum dot (QD) structures into a single junction device.
[2] Findings related with chemically-synthesized colloidal quantum dots (CQDs)[7] and perovskite-based photovoltaic materials have shown potentially favorable conditions to realize IB semiconductors.
CQDs made of low-bandgap (in near-infrared) materials allow strong carrier confinement, high radiative lifetimes, large Bohr radius,[8] and can overcome the main aforementioned limitations of epitaxially-grown dots.
[6] Moving forward, more research is needed to find materials with natural partially filled IB bands.
[15] Krich, however, disproved this and in the process proposed a “figure of merit” to determine if materials would be suitable for high efficiency IB's.
[15] The idea was that if the non-radiative recombination lifetime was significantly higher than the transit time for an electron to move from the conduction band to the IB, then the material could increase efficiency.
Chalcogen doped silicon, in particular, have low figures of merit due to their small non-radiative recombination lifetimes.
[16] To achieve IB devices, more research needs to be done to find a bulk semiconductor material that exhibits higher non-radiative recombination lifetimes.