A) Microcell design B) Microcell fabrication scheme C)SEM of fabricated microcells D) optical image of microcell array
While silicon solar panels corner a large part of the current solar energy market, they are still too expensive to compete directly with fossil fuels. However, new advances in silicon solar microcells bring increases in process reliability, efficiency and cost, making solar energy more scalable and affordable.
In their recent paper, Yao et. al demonstrate a redesigned silicon solar µ-cell which incorporates a thermal oxide as a robust etching and diffusion mask, which also serves as an anti-reflection and surface passivation coating. They also put forth design criteria optimizing the spatial distribution of µ-cells to maximize light-trapping and for the integration of backside reflectors and polymer waveguides into devices for optimal performance.
The figures of merit for the champion device are an open-circuit voltage of 0.534 V, a short-circuit current density of 28.7 mA cm-2, a fill-factor of 0.762 and an overall efficiency of 11.7%. Interestingly, they demonstrate the efficacy of the thermal oxide as a passivation layer by testing a device before and after the oxide is etched off, showing that removing the oxide causes a significant decrease in performance. They also show that the incorporation of backside reflectors and planarization layers significantly enhances device performance.
An important consideration for any emerging solar energy technology is scalability. These redesigned silicon solar µ-cells have a peak-power-generation referenced silicon consumption of only 0.4 g Wp-1, substantially lower than the 10 g Wp-1 of commercially available silicon solar cells. Combined with the scalability of the processing steps used in the µ-cell fabrication, the low amount of silicon required could be a huge step forward in reducing the cost of solar energy.
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Fabrication and assembly of ultrathin high-efficiencysilicon solar microcells integrating electrical passivation and anti-reflection coatings
Yuan Yao, Eric Brueckner, Lanfang Lib and Ralph Nuzzo
DOI:10.1039/C3EE42230E
