The Mission

The project's mission is to improve the aesthetic variety and design flexibility, as well as further reduce the environmental impact of solar cells - specifically dye-sensitised solar cells in the format of "Photovoltaic Photographs" - using bacterially derived pigments. When we talk about solar cells, we typically think of the solid, large, blue panels we place on our roofs. These are first-generation, silicon-based solar cells. These cells, however, lack the aesthetic flexibility that architects and building managers usually seek, which often discourages their integration into buildings and urban spaces. By further diversifying the appearance of solar cells, we can encourage further integration of solar technologies, thus meeting this project's ultimate goal; to increase solar energy usage.

The Challenge

Although solar technologies have existed since the 19th century, they have yet to be fully integrated or adopted as our primary energy source [1]. Modern industries and infrastructure still rely heavily on fossil fuels for energy production [2]. Several factors contribute to this slow transition, one of which is the limited visual and aesthetic variety of solar cells (SCs) — specifically silicon-based SCs [2]. Silicon SCs, the first generation of photovoltaics (PVs), offer limited colour and design options, making them less adaptable and less favourable to architects and building managers [4,5,6]. This aesthetic rigidity often discourages their integration into buildings and urban spaces, ultimately reducing opportunities for large-scale solar adoption [4,5,6]. As a result, renewable energy generation remains limited, reinforcing our continued dependence on fossil fuels [4,5,6]. This challenge has driven growing interest in third-generation PVs — including organic SCs, perovskite SCs, and dye-sensitised SCs (DSSCs) — which combine sustainability with aesthetic flexibility [6,7,5]. Compared to their silicon counterparts, these newer PVs are more cost-effective, easier to integrate into smart applications (e.g. transparent solar windows and wearable devices), have a smaller environmental impact, and offer extensive customisation in both colour and design [9,10,5]. In parallel, an emerging research direction focuses on further enhancing the sustainability of these technologies through the development of bio-based photovoltaics and bio-photovoltaics [11]. These approaches incorporate renewable, plant-derived, or bacterial-based materials as functional components — particularly in DSSCs — to reduce environmental impact while introducing new possibilities for colour and transparency [11]. In this way, material sustainability and aesthetic variability are closely intertwined: bio-based pigments can simultaneously provide a broader palette of natural colours and patterns while improving the environmental profile of these devices [11]. Building on this relationship between function and form, multiple routes can be taken to enhance the customisability of PVs, including semi-transparency, colour integration, and/or pattern/image integration [3]. These design aspects can be achieved through various fabrication techniques: for instance, colour can be applied via spray coating or inkjet printing [5], while patterning or image integration can be done using laser scribing, foil wrap layering, or the pixel/mosaic technique [5]. Although each of these methods has distinct advantages, they tend to be size-dependent and/or time-consuming. To overcome these constraints, Husting et al. (2022) introduced the concept of “photovoltaic photographs” (PVPHs). Based on anthotype photography, PVPHs unify all the aforementioned aesthetic elements — integrating semi-transparent, multicoloured patterns and high-resolution images directly into the photoactive layer of DSSCs, irrespective of size. This is done using a light-induced process known as photobleaching [9]. Following their conceptual development, PVPHs were translated to a practical application in DSSCs, leveraging their aesthetic versatility, low production cost, and methodological similarity to anthotype photography [5]. Despite this progress, PVPH technology remains in its early stages, particularly regarding visual and colour diversity [5]. To date, only monochrome yellow and orange PVPHs have been reported, highlighting the need for further research into expanding their chromatic range and design complexity [5]. References 1. Fraas, L. M. (2014). History of solar cell development. In Springer eBooks (pp. 1–12). https://doi.org/10.1007/978-3-319-07530-3_1 2. Tripanagnostopoulos, Y., Leftheriotis, G., Vradis, A., Anastasopoulos, D., Spiliopoulos, N., Priftis, P., Manariotis, I., Lianos, P., & Stathatos, E. (2014). SOLAR ENERGY MATERIALS AND SYSTEMS FOR AN AESTHETIC AND SUSTAINABLE FUTURE. Contemporary Materials, 5(2). https://doi.org/10.7251/comen1402172t 3. Bao, Qifang, Honda, Tomonori, El Ferik, Sami, Shaukat, Mian Mobeen, and Yang, Maria C. Understanding the role of visual appeal in consumer preference for residential solar panels. In: Renewable Energy 113 (2017), pp. 1569–1579. https://doi.org/10.1016/j.renene.2017.07.021. 4. Sanchez-Pantoja, Nuria, Vidal, Rosario, and Pastor, M. Carmen. Aesthetic impact of solar energy systems. In: Renewable and Sustainable Energy Reviews 98 (2018), 227–238.https://doi.org/10.1016/j.rser.2018.09.021. URL: https://www.sciencedirect.com/science/article/abs/pii/S1364032118306695?via%3Dihub 5. Hustings, Jeroen, Fransaert, Nico, Vrancken, Kristof, Cornelissen, Rob, Valcke, Roland, and Manca, Jean V. Photovoltaic photographs. In: Solar Energy Materials and Solar Cells 246 (2022), p. 111917. https://doi.org/10.1016/j.solmat.2022.111917. URL: https://www.sciencedirect.com/ science/article/pii/S0927024822003361. 6. Tobin LL, O’Reilly T, Zerulla D, and Sheridan JT. Characterising dye-sensitised solar cells. Optik 2011 Jul; 122:1225–30. DOI: 10.1016/j.ijleo.2010.07.028 7. Cavinato LM, Fresta E, Ferrara S, and Costa RD. Merging Biology and Photovoltaics: How Nature Helps Sun-Catching. Advanced Energy Materials 2021 May; 11:2100520. DOI: 10.1002/aenm.202100520 8. Villarreal CC, Monge S, Aguilar D, Tames A, Araya N, Aguilar M, Ramakrishna S, Thavasi V, Song Z, Mulchandani A, and Venkatesan R. Bio-sensitized solar cells built from renewable carbon sources. Materials Today Energy 2021; 23:100910. DOI: 10.1016/j.mtener.2021.100910 9. Orona-Navar A, Aguilar-Hernandez I, Nigam K, Cerd ´ an-Pasar ´ an A, and Ornelas-Soto N. Alternative sources of natural pigments for dye-sensitized solar cells: Algae, cyanobacteria, bacteria, archaea and fungi. Journal of Biotechnology 2021 May; 332:29–53. DOI: 10.1016/j.jbiotec.2021.03.013 10. Shah W, Faraz SM, and Awan ZH. Photovoltaic properties and impedance spectroscopy of dye sensitized solar cells co-sensitized by natural dyes. Physica B: Condensed Matter 2023 Apr; 654:414716. DOI: 10.1016/ j.physb.2023.414716 11. Villarreal CC, Monge S, Aguilar D, Tames A, Araya N, Aguilar M, Ramakrishna S, Thavasi V, Song Z, Mulchandani A, and Venkatesan R. Bio-sensitized solar cells built from renewable carbon sources. Materials Today Energy 2021; 23:100910. DOI: 10.1016/j.mtener.2021.100910

The solution

To address the aesthetic diversity issues present, as well as improve the sustainability of PHPVs, this project will be investigating whether a broader variety in colour can be obtained in PVPHs, through the application of bacterially derived dyes — a domain that is yet to be explored within the bio-photovoltaics research field. Bacterial pigments could provide a more sustainable alternative to the synthetic pigments currently being used on DSSCs. Synthetic dyes tend to be volatile in nature, as well as both time- and financially costly to produce. On the other hand, bacterial pigments, are not only natural, but readily available for extraction, thus minimizing production time and funds necessary. The properties of the bacterial pigments and PHPVs will be evaluated in terms of: (i) absorption spectra (UV-Vis analysis) (ii) current-voltage (IV) measurements, and (iii) LBIC (laser beam induced current) mapping. The use of these techniques aims to address the following research questions, respectively: (a) Which diversity of colour can be obtained with bacterially derived pigments? (b) What is the photovoltaic performance of PVPHs based on bacterial pigments? (c) How does photobleaching affect the local efficiency of bacterial pigments in converting sunlight?