Nowadays, technological devices has become an essential part of all our lives. Therefore, a large amount of energy has to be generated to enable this level of energy consumption. Although, in recent years there has been an increasing interest in renewable energy generation driven by government policies and the social awareness, but, the energy we consume today still is mostly generated from fossil fuels. The key question is how to maintain our live style without affecting environment further. The answer is, move towards a greener energy generation and meet the net-zero target that has been established. The renewable energy generation technologies available can all contribute towards a comprehensive strategy. Photovoltaic solar cells (PVSC) are already playing a key role towards cleaner energy generation. The Earth receives enough sunlight in a single day (free to access for everyone) to satisfy the current level of energy demand for 27 years and the current level of the technology involved is offering very promising performance.
The solar cell market is dominated by crystalline Silicon (c-Si) PVSCs which have experienced a steady improvement to achieve 26.5% Power Conversion Efficiency (PCE) for a single junction, almost reaching it theoretical efficiency limit set by Shockley-Queisser. However, as 180-300 m thick costly c-Si layer is needed for near complete light absorption, which accounts to 40% of the cost, so the payback time although it has been significantly reduced over the last decade, but it is rather long. To reduce the cost, 2nd generation PVSC explored 2-3 m thick thin-film but efficiency has been poor. Current third generation solar cell research, dominated by thin organic perovskite based PVSC, is showing a good efficiency, however, its stability issue and use of toxic Lead (Pb) need to be addressed before commercialization.
As the Si PVSC technology is very mature, only reduction in its price will be the key to encourage its wider and faster adoption. One of the techniques used to improve the efficiency, is texturing the surface of a thin Si PVSC with an array of geometrical patterns such as pyramids, inverted pyramids, NanoWires (NW) and nanoholes. The purpose of introducing a texturing pattern is to effectively increase the number of times sunlight is incident on the solar cell due to multiple reflections between the elements of the pattern which leads to an increase in the absorption. It has been reported that the Lambertian limit of light trapping can be achieved by an ideal rough surface where incident light is randomly scattered increasing the optical path length. The optical path can be increased by 50 times (for Si NW), which can allow to reduce silicon wafer thickness from 200-300 µm to just 4-6 µm, nearly 2 orders of magnitude reduction, resulting a significant potential cost reduction.
Nevertheless, with so many different patterns available, it is important to determine which pattern offers better performance. This is one of the questions that this project has been able to answer. We have also identified how the often-forgotten short NWs can be used to mimic the performance of Anti Reflection Coating layers. Then, following this logic, we have successfully mimic 2 and 3 layers ARC using NWs.
