New concepts and materials for solar power conversion

In the presentation I will introduce various new concepts for high efficiency conversion of solar energy. The core presentation will focus on two research areas: group III-nitrides for high efficiency multijunction solar cells and highly mismatched alloys for multiband solar and photoelectrochemical cells.

The discovery of the low band gap of InN greatly expanded the range of the direct gaps of group III-nitride alloys from 0.64 in InN to 6.1 eV in AlN. Therefore In_1-xGa_xN and In_1-yAl_yN alloys are promising materials for high efficiency solar cells, as their band gaps are continuously tunable across the solar spectrum. The large electron affinity (5.8 eV) of InN offers a unique opportunity of matching the conduction band edge of group III-In-nitride alloys to the valence band of standard semiconductors such as Si and Ge. The low resistance contact between n-InGaN and p-Si has been demonstrated for InGaN films grown on S. Latest results on practical realization of InGaN/Si tandem cells will be presented and remaining challenges will be discussed.

The second part of the presentation will be devoted to recent progress in synthesis of highly mismatched alloys (HMAs). Such alloys exhibit unusual optical and electrical properties and with a proper choice of component materials allow for an independent engineering of band gaps and band offsets. We have synthesized group II-VI dilute oxides and group III-V dilute nitride HMAs. The alloys have a unique band structure with a narrow intermediate band in the band gap of the host material. We have designed fabricated and tested first intermediate band solar cell using GaNAs HMA as an absorber material. I will also present our most recent results on successful synthesis of GaNAs alloys in the whole composition range and discuss potential use of these materials in photoelectrochemical cells for solar water dissociation.