Ultra-thin, high performance crystalline silicon tandem cells fabricated on a glass substrate

•We present that the anodic bonding process is a useful technique to develop the ultrathin film device.•We develop a nanoscale inverted pyramid structure to enhance the light absorption.•We address the parasitic electrical and optical losses by material engineering.•We achieve an impressive high efficiency of up to 13.6% for the ultra-thin tandem cells (sub-8 μm-thick)

Ultrathin silicon provides a viable pathway towards the realization of photovoltaic devices aimed at reducing material usage, utilizing low quality material and diversifying their application. However, solar cells based on the ultrathin film reported thus far are still far from fully optimized compared with their crystalline, wafer-based counterparts due to insufficient light absorption. Furthermore, fabrication of these ultrathin devices on an inexpensive substrate, such as glass and plastic, is still a critical issue at present. Here we present an approach to fabricate ultrathin, high performance silicon solar cells with a tandem structure on a glass substrate. The strategy involves transferring the ultrathin film to the glass substrate by applying an anodic bonding process, introducing a nanoscale inverted pyramid light trapping structure that is suitable for conformal deposition to enhance light absorption, and engineering doped layers to avoid parasitic optical and electrical losses. We demonstrate a-Si/c-Si tandem solar cells with high efficiencies of up to 13.6%, using a 300 nm thick a-Si top cell and a sub-8 μm-thick silicon bottom cell. This significant improvement of the efficiency is achieved even without the complicated passivation process normally applied in high-efficiency silicon solar cells. Our results are an important step toward high-efficiency ultrathin solar cells for the future.

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