Increasing light absorption is one of the most effective approaches to boost up the performance of photovoltaic (PV) devices. More specifically, light absorption in solar cell devices is directly resulted in the amount of current generated by the devices. Therefore, an effective light management technique is upmost important for solar cells. However, it is challenging for thin film solar cells due to its short optical path in the light absorbing layers. Recently, the incorporation of nanostructures, such as nanowires, nanopillars, nanopyramids, into solar cells have demonstrated an significant enhancement in light aborption. However, the scalability of these stuctures is limited by costly nanostructure fabrication processes. Furthermore, in daily operation, dust accumulation on...[ Read more ]

Increasing light absorption is one of the most effective approaches to boost up the performance of photovoltaic (PV) devices. More specifically, light absorption in solar cell devices is directly resulted in the amount of current generated by the devices. Therefore, an effective light management technique is upmost important for solar cells. However, it is challenging for thin film solar cells due to its short optical path in the light absorbing layers. Recently, the incorporation of nanostructures, such as nanowires, nanopillars, nanopyramids, into solar cells have demonstrated an significant enhancement in light aborption. However, the scalability of these stuctures is limited by costly nanostructure fabrication processes. Furthermore, in daily operation, dust accumulation on solar cell surfaces leads to a serious decline in light absorption and, eventually, hurts the performance of solar cells. A regular cleaning may cause a high maintenance cost due to the precious water resources and expensive manpower. Eventually, it hampers the attractiveness of deploying PV systems, especially in dessert areas. A low-cost dust cleaning technique is urgently needed to relieve this problem.

In this thesis, novel 3-D nanostructure antireflection techniques have been demonstrated using high-performance PV devices. Two different types of techniques, substrate-based and surface-based, have been developed and scaled up to demonstrate its enhancement in PV devices. For the substrate-based AR techniques, 3-D nanostructured nanospike arrays has been fabricated as the bottom substrate for amorphous-Si (a-Si) solar cells. AR effect and device performance for different pitches, regularities, structural geometries have been studied. Due to the multiple light-scattering effect within the nanospike structures, effective AR effect can be achieved in the a-Si solar cells leading to 37% more light absorption and 43% improvement in device efficiency.

Besides the substrate-based AR techniques, surface-based nanostructured AR films have been developed to minimize the light reflection on the front surfaces. Commercial PV devices or panels are covered by glass for protection. Large amount of light is reflected out due to the mismatch of refractive index at the glass-air interface. Optimal nanostructure arrays on the transparent plastic film can significant reduce the surface light reflection owing to the unique properties of nanostructures: gradient change of refractive index and multiple scattering of light. Around 4% of reflectance reduction can be observed after applying the film on CdTe solar cell devices. The AR effect is onmidirectional and more pronounced in large light incident angle, leading 7% enhancement in daily energy output. Similar improvement is observed in crystalline-Si (c-Si) solar cells so that the effect is universal for all types of solar cell devices. In addition, the superhydrophobic nanostructured surface can be achieved for self-cleaning functions to prevent dust from accumulation. Finally, a roll-to-roll fabrication process has been developed to massively produce the nanostructured film with satifactory performance.