Colloidal Lithography for Photovoltaics: An Attractive Route for Light Management

Abstract

The pursuit of ever-more efficient, reliable, and affordable solar cells has pushed the development of nano/micro-technological solutions capable of boosting photovoltaic (PV) performance without significantly increasing costs. One of the most relevant solutions is based on light management via photonic wavelength-sized structures, as these enable pronounced efficiency improvements by reducing reflection and by trapping the light inside the devices. Furthermore, optimized microstructured coatings allow self-cleaning functionality via effective water repulsion, which reduces the accumulation of dust and particles that cause shading. Nevertheless, when it comes to market deployment, nano/micro-patterning strategies can only find application in the PV industry if their integration does not require high additional costs or delays in high-throughput solar cell manufacturing. As such, colloidal lithography (CL) is considered the preferential structuring method for PV, as it is an inexpensive and highly scalable soft-patterning technique allowing nanoscopic precision over indefinitely large areas. Tuning specific parameters, such as the size of colloids, shape, monodispersity, and final arrangement, CL enables the production of various templates/masks for different purposes and applications. This review intends to compile several recent high-profile works on this subject and how they can influence the future of solar electricity.

Soft-Microstructured Transparent Electrodes for Photonic-Enhanced Flexible Solar Cells

“…Figure 3b-f corresponds to O2 RIE engravings with a duration of 90-450 s. The shorter plasma exposure times lead to only a small reduction in the spheres' size and, consequently, a thinner linewidth of the resulting IZO mesh, while longer etching times lead to a stronger particle reduction (i.e., larger inter-particle separation), promoting higher IZO infiltration. However, care must be taken to avoid prolonging the O2 etching time too much (in this case above ~500 s), because if there is an excessive reduction in the particles' size they will be strongly deformed, making them unsuitable for use as masks in the CL patterning, as also observed in previous contributions from the authors [6,23,31]. The surface morphology of the microstructures was also studied using AFM, mainly to verify the vertical profile (height) of the final mesh, which was set by the IZO sputtering time.…”

“…A lithographic mask can be promptly achieved via CL, whose pattern resolution is entirely dependent on the colloidal size that can be deposited in high-quality monolayer arrays. The best achieved resolutions in the literature ranges between 50 nm and 200 nm, which is comparable to that of state-of-the-art conventionallithography systems [23,28]. Moreover, the fabricated structures can be produced with a high accuracy on a large scale, as the method is not limited in terms of the deposition area, meaning that it offers the possibility to be adapted to mass production techniques such as roll-to-roll.…”

“…Among the nano/micro-patterning strategies capable of fabricating these LT structures, nano-imprint lithography (NIL) and colloidal lithography (CL) have sparked the highest research interest for PV applications [22][23][24][25]. However, NIL is limited in terms of the materials that can be structured, and presents difficulties concerning scalability due to its poor pattern fidelity over large areas.…”

“…The photonic structures fabricated by this versatile soft-lithography CL method can be implemented in PV devices in a straightforward manner, demonstrating pronounced performance improvements [25,31,32]. Moreover, metallic micro-meshed electrodes can also be obtained by CL, which is currently considered one of the most promising approaches for producing industrially compatible transparent conducting materials with excellent optical transmittance and electrical conductance [23,33,34].…”

Simple Self-Assembly Strategy of Nanospheres on 3D Substrate and Its Application for Enhanced Textured Silicon Solar Cell

“…The development of nanomaterials and nanostructures provides new opportunities for performance boosting of optical and optoelectronic devices [ 1 , 2 , 3 , 4 , 5 ]. For example, dielectric nanostructures are used to enhance the transmission and brightness of different transparent windows or display screens [ 6 , 7 , 8 , 9 ], and plasmonic or dielectric nanocoatings are widely proposed and applied to enhance the efficiency of photovoltaic devices or sensitivity of photodetectors [ 1 , 10 ].…”