Biomimetic Approaches to "Transparent" Photovoltaics: Current and Future Applications

Abstract

There has been a surge in the interest for (semi)transparent photovoltaics (sTPVs) in recent years, since the more traditional, opaque, devices are not ideally suited for a variety of innovative applications spanning from smart and self-powered windows for buildings to those for vehicle integration. Additional requirements for these photovoltaic applications are a high conversion efficiency (despite the necessary compromise to achieve a degree of transparency) and an aesthetically pleasing design. One potential realm to explore in the attempt to meet such challenges is the biological world, where evolution has led to highly efficient and fascinating light-management structures. In this mini-review, we explore some of the biomimetic approaches that can be used to improve both transparent and semi-transparent photovoltaic cells, such as moth-eye inspired structures for improved performance and stability or tunable, coloured, and semi-transparent devices inspired by beetles' cuticles. Lastly, we briefly discuss possible future developments for bio-inspired and potentially bio-compatible sTPVs.

Keywords: biomimetic; semi-transparent photovoltaics; transparent photovoltaics.

Figure 1

Visual schematisation of the three key factors in the design of TPVs and sTPVs.

Figure 2

Difference in colour-rendering capabilities between high and low CRI. Reprinted with permission from Ref. [6]. 2017, Springer Nature: Nature Energy.

Figure 3

Beetles’ cuticle inspired sTPVs. (a) Schematic of a beetle’s cuticle. (b) Schematic of the spectrally selective electrodes. (c) Montage showing spectrally selective electrodes of different colours, obtained by tuning the thickness and number of different dielectric layers for the transmission of a specific colour. Here, PDINO stands for perylene diimide functionalized with amino N-oxide, ITO stands for indium tin oxide, PM6 stands for poly[[4,8-bis[5-(2-ethylhexyl)-4-fluoro-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl [5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]-2,5-thiophenediyl], N3 stands for azide, PC₇₁BM stands for [6,6]-Phenyl-C71-butyric acid methyl ester, and PEDOT:PSS stands for poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Adapted with permission from Ref. [31]. 2020, American Chemical Society.

Figure 4

Structure of the eye of a Mourning Cloak butterfly (Nymphalis Antiopa) on different length scales. (a) Macroscale. (b) Microscale. The hexagonal close-packed pattern is clearly visible. (c) Mesoscale. Each hexagon of the pattern is around 20 µm wide. (d) Nanoscale. The average nipple diameter is 170 nm. Adapted with permission from Ref. [34]. 2016, license CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/ (accessed on 19 April 2022)).

Figure 5

(a) Moth compound eye and schematic of the moth-eye inspired structure. (b) Illustration of the fabrication process of the sTPV device based on Cs_0.05FA_0.83MA_0.12PbBr_0.33I_0.27 perovskite. Here, PS stands for polystyrene, ALD for atomic layer deposition, Spiro-OMeTAD for 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene, and IZO for indium zinc oxide. Adapted with permission from Ref. [35]. 2021, license CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/ (accessed on 19 April 2022)).

Figure 6

Schematic representation of the roll-to-roll printing process of the moth-eye film from Ju et al. Reprinted with permission from Ref. [53]. 2020, IOP Publishing.

Figure 7

Schematic representation (left) of the transparent super-hydrophobic film and picture (right) of a glass slide coated with it showing both its transparency and super-hydrophobicity. Here, PAH stands for poly(allylaminehydrochloride) and SPS for Poly(sodium4-styrenesulfonate). Adapted with permission from Ref. [42]. 2007, American Chemical Society.

Figure 8

Bombyx Mori cocoons (left), schematic representation of the PV device (centre), and picture of the finished device (right). Here, PFN stands for poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] and PTB7 stands for poly [[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]. Reprinted with permission from Ref. [60]. 2014, American Chemical Society.

Figure 9

Schematic representation of the semi-transparent thin-film LSC implementing the negative PDMS replica layer of leaves’ microstructures. Reprinted with permission from Ref. [69]. 2022, license CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/ (accessed on 20 October 2022)).