Photovoltaic (PV) cells have low maintenance costs, no moving parts, operate at near ambient temperature, and enable energy generation at any scale. As Silicon-based solar cells are non-toxic, efficient, and extremely robust, the vast majority of commercial PV module production are silicon based. Solar cell efficiencies can be improved by absorbing more incident photons to create more photocarriers and/or collecting more photocarriers to generate a higher current. The employment of surface nanostructures allows the capturing of more light owing to their large surface-area-to-volume ratio, and quantum confinement effects. The ENERGOSIL (Silicon films on metals for energy applications) project worked on finding new silicon surface treatment methods to increase its efficiency in solar energy harvesting. Silicon surface nano-micro architectures were successfully created, which absorb about 99 % of the incident light. By engineering the reflective and refractive properties of solar cell surfaces, light can be trapped within the active region more efficiently. Better photon trapping allows for physically thin, but optically thick active layers in the solar cells, which not only reduces the processing costs and amount of material used, but also decreases electrical losses during photocarrier transport. The team investigated the electrochemistry of molten salts and ionic liquids. They developed new technologies, which are promising not just for PV cells, but also for the production of chemical sensors and hydrogen photo-generators. The method was based on the FFC-Cambridge process, where a silicon disk with a surface layer of oxide is exposed to a cathodic potential. This causes the oxygen in the oxide to ionise and dissolve into the salt, leaving a matrix of silicon needles. This creates a black surface able to absorb up to 99 % of the incident light over a wide range of wavelengths. ENERGOSIL created distinctive surface architectures, which could be applied for the production of efficient heat-concentrating solar energy devices. The results have been published and patented. A company, BlackSilicon Ltd, has been formed to develop the technology further.
Silicon, solar energy, solar cell, photovoltaic, nanostructure, quantum confinement, FFC-Cambridge process