conditions. This makes difficult to further reduce the cost of electricity production. [7,8] Furthermore, although solar energy is a renewable source, it does not mean that any kind of photovoltaics (PV) is sustainable. For instance, silicon is an essential material in electronics and solar industries and, up to date, is irreplaceable. Despite its abundancy in Earth's crust, it is for the vast majority (80%) present as ferrosilicon, whose purification is expensive and highly pollutant. The production of 1 ton of silicon requires 6 tons of raw materials, almost 3 tons of Quartz, 1.5 tons of reducing agents, 1.5 tons of wood and 13 000 kWh of energy. [9,10] Therefore, in 2014 the EU commission included silicon metal in the critical raw material (CRM) list. [11] In this context, the third generation PV has reborn, offering cost-effective and efficient CRM-free devices with a lower reliance on the incident angle of light and integration in smart-end applications, like flexible and wearable devices, [12][13][14] fully transparent solar cells and windows, [15,16] and biocompatible devices. [17][18][19] The leading third generation SCs are organic solar cells (OSCs), [20][21][22] perovskite solar cells (PSCs), [23][24][25][26][27] and dye-sensitized solar cells (DSSCs). [28][29][30] Despite their versatile applications and high performances, sustainability still represents a major issue toward becoming an ideal energy technology in the mid-long term future. Among others, fullerene-based materials are toxic, [31] indium tin oxide (ITO) is brittle, chemically unstable, and expensive due to limited indium sources on Earth's crust. [32,33] Cobalt is also listed as CRM, [11] while cadmium, selenium, lead and ruthenium are toxic materials. [34,35] With regard to flexible devices, polyethylene terephthalate (PET) is the standard substrate; though its environmental footprint is critical and its nonbiodegradable properties lead to harmful effects in living organisms. [36] This has fueled a strong cooperation among the fields of engineering, biology, chemistry, and physics to discover new strategies for cost-effectiveness preparation and implementation of bio-derived materials in highly performing PVs.In general, this cooperation constitutes a part of the emerging and multidisciplinary field of biophotonics, [37] which involves biomedical optics, [38] living light, [39][40][41] biomimetic, biomaterials and bioengineered compounds, as well as fabrication/implementation methods applied to optoelectronics [42] and photonics, [43] among others. For instance, artificial lightning and biology have been recently merged with the implementation of cellulose, chitosan, silk, and fluorescent proteins as Accomplishing sustainability in optoelectronics, in general, and photovoltaics (PV), in particular, represents a crucial milestone in green photonics. Third generation PV technologies, such as organic solar cells (OSCs), perovskite solar cells (PSCs), and dye-sensitized solar cells (DSSCs) have reached a mature age and are slowly making thei...
