Wide angle light collection with ultralow reflection and super scattering by silicon micro-nanostructures for thin crystalline silicon solar cell applications

Abstract

Conventional c-Si solar cells employ micron-sized pyramids for achieving reduced reflection (∼10%) and enhanced light trapping by multiple bounces (maximum 3) of the incident light. Alternatively, bio-mimetic, moth-eye sub-wavelength nanostructures offer broadband antireflection properties (∼3%) suitable for solar cell applications in the optical regime. However, such structures do not provide any advantage in the charge carrier extraction process as radial junctions cannot be formed in such sub-wavelength dimensions and they have high surface area causing increased charged carrier recombination. The choice of the geometry for achieving optimum photon–electron harvesting for solar applications is therefore very critical. Cross-fertilization of the conventional solar cell light-trapping techniques and the sub-wavelength nanostructures results in unique micro-nanostructures (structures having sub-wavelength dimensions as well as dimensions of the order of few microns) which provide advanced light management capabilities along with the ability of realizing radial junctions. It is seen that an ultralow reflection along with wide angle light collection is obtained which enables such structures to overcome the morning, evening and winter light losses in solar cells. Further, super-scattering in the structures offer enhanced light trapping not only in the structure itself but also in the substrate housing the structure. Ray and wave optics have been used to understand the optical benefits of the structures. It is seen that the aspect ratio of the structures plays the most significant role for achieving such light management capabilities, and efficiencies as high as 12% can be attained. Experiments have been carried out to fabricate a unique micro-nanomaze-like structure instead of a periodic array of micro-nanostructures with the help of nanosphere lithography and the MacEtch technique. It is seen that randomized micro-nanomaze geometry offers very good antireflection properties (∼1%) which are close to the expected optical behaviour of the periodic array at a much lower surface area.

Black silicon solar cell: analysis optimization and evolution towards a thinner and flexible future

“…It is seen that AR between 2 and 3 is optimum for such solar cells. Efficiency remains unaffected for a limited range of incidence angles (±35°) even for an optimized geometry while the simulated integrated reflectance remains unchanged for incidence angles (±55°) (figure 5) calculated as per the previous work of the authors [22]. This is because the cosine effect has been taken into consideration while calculating the efficiency.…”

The Role of Graphene and Other 2D Materials in Solar Photovoltaics

“…Different light-trapping schemes along with extrinsic (bulk and surface) recombination mechanisms have been implemented in thin absorbers to achieve higher solar-cell efficiency. [69,71,72] With the need for emerging photovoltaic cells to be fabricated on bendable supports and capable of high-speed roll-to-roll (R2R) processing, silicon is gradually evolving toward a "flexible" future achieving a flexibility at a thickness below ≈50 µm. [73][74][75] Such flexible silicon substrates would result in a more efficient use of silicon but will need improvement in wafer manufacturing, sawing technologies, reduced kerf loss, new handling concepts, and modified encapsulation techniques.…”

“…Therefore, influence of silicon absorber thickness on the solar‐cell performance has been perhaps the most critical factor. Different light‐trapping schemes along with extrinsic (bulk and surface) recombination mechanisms have been implemented in thin absorbers to achieve higher solar‐cell efficiency . With the need for emerging photovoltaic cells to be fabricated on bendable supports and capable of high‐speed roll‐to‐roll (R2R) processing, silicon is gradually evolving toward a “flexible” future achieving a flexibility at a thickness below ≈50 µm .…”