Stacked Back Reflector Architecture for Advanced Optical Management in State-of-the-Art Single-Junction μc-Si:H Solar Cells

The present work deals with an advanced technology for efficient light management through back reflection in thin silicon based solar cells, in particular, single-junction microcrystalline silicon (μc-Si:H) solar cells. Semiconductor nanoparticles (Ag2S NPs) have been chosen to design the back reflector layer (BRL) by embedding them within two thin layers of indium tin oxide (ITO). Owing to its nominal parasitic light absorption over a broad wavelength region (300-1100 nm), the Ag2S NPs can reflect back a notable amount of light that were supposed to get transmitted through the relatively less thick (~2 μm) active microcrystalline Si layer, and hence, can function like nanomirrors. Encapsulation of the Ag2S NPs between the ITO layers provides chemical and physical stability to the nanomirrors. By placing such BRL at the back of this p-i-n based superstrate structure, a significant amount of light (>90%), mainly in the red and near infrared (NIR) region, was found to reflect back to the cell and this resulted in a state-of-the-art photoconversion efficiency of 9.36% for single-junction μc-Si:H solar cells. The reported value is one of the best in the class. As the main light absorption zone for μc-Si:H falls in the red and NIR region (bandgap energy of μc-Si:H is 1.1-1.2 eV), such back reflections become worthy. The experimentally observed facts have also been validated through theoretical simulations.