Light trapping structure with backside scatterer for enhanced photo-absorption by quantum structures

A strategy is demonstrated that maximizes the contribution of quantum structures for third-generation cells such as an intermediate-band cell: an optical cavity composed of (1) an optically-thin substrate in the absorption range of a quantum structure and (2) a backside scatterer that reflects light to the direction allowing total reflection. An InGaAs/GaAsP multiple quantum wells (MQWs) were used as an example of quantum structures and the effect of optical cavity was evaluated in terms of an enhancement in the external quantum efficiency (EQE) in the wavelength range 850-1000 nm. A PV cell using a semi-insulating GaAs substrate and front contact has been employed for proof of concept. Two kinds of backside scatterers were examined: a self-assembled array of Ag nanoparticles and a periodic groove texture by lithography and wet etching. Both the structures enhanced the EQE for the MQWs by approximately 20-30% and further enhancement is expected by improving the scattering efficiency and the use of an ultra-thin substrate with a light-scattering back contact.