Investigation of boron antimonide as hot carrier absorber material

Hot carrier solar cells (HCSCs) are a high-efficiency third generation solar cell concept. One major difficulty in realizing HSCSs is the delay of the hot carrier cooling process in their absorber. Bulk boron antimonide (BSb) was investigated with ab initio methods for its potential as hot carrier absorber (HCA). Our calculation results of its phononic structure show that several phonon decay processes are suppressed, leading to a phonon bottleneck and a considerable delay of carrier cooling. Results on its electronic structure reveal a low electron effective mass and an indirect band gap of 0.59 eV. Surprisingly high experimental values of the absorption coefficient near band gap are explained by distinct features of the electronic and phononic band dispersions and provide favorable optical properties for a HCA.

► Wide phononic bandgap and associated phonon bottleneck; slowed down carrier thermalization.
► Optimal electronic bandgap for hot carrier solar cells. Together with its phononic properties, our results show that BSb is a very attractive material for hot carrier absorbers.
► High absorption near indirect bandgap explained by hot-phonon assisted transition.
► Low electron effective mass.