Improved photon absorption in thin-film solar cells for integration into radiation tolerant multijunction photovoltaics

Loss in output power in multi-junction space photovoltaics occurs due to reduction in minority carrier diffusion length caused by on-orbit radiation damage of the crystal. One method to improve the radiation resistance of a multi-junction device is through thickness reduction of the various layers, increasing carrier collection at reduced diffusion length. However, this reduction in thickness can also result in current loss unless some type of mirror is used to increase the optical path length (OPL). In this talk, we will explore two options for increasing the OPL in the middle and bottom junction of a standard InGaP2/GaAs/In0.3Ga0.7As inverted metamorphic (IMM) solar cell using a chirped distributed Bragg reflector (DBR) between the GaAs and InGaAs cell and using a maskless texture at the back side of the InGaAs cell. The fabrication of these structures will be reviewed as well as device and radiation improvements afforded by application of the photonic structures.