Biodeterioration Affecting Efficiency and Lifetime of Plastic-Based Photovoltaics

Abstract

The low environmental impact of electricity generation using solar cells crucially depends on high energy-conversion efficiencies, long lifetimes, and a minimal energy and material demand during production. Emerging thin-film photovoltaics such as perovskites on plastic substrates could hold promises to fulfill all these requirements. Under real-world operating conditions, photovoltaic operation is challenged by biological stressors, which have not been incorporated for evaluation in any test. Such stressors cause biodeterioration, which impairs diverse, apparently inert materials such as rock, glass, and steel and therefore could significantly affect the function and stability of plastic-based solar cells. Given that different photovoltaic technologies commonly use similar materials, the biodeterioration mechanisms reviewed here may possibly affect the efficiency and lifetimes of several technologies if they occur sufficiently faster (during the expected lifetime of photovoltaics). Once the physical integrity of uppermost module layers is challenged by biofilm growth, microbially mediated dissolution and precipitation reactions of photovoltaic functional materials are very likely to occur. The biodeterioration of substrates and seals also represents emission points for the release of potentially harmful photovoltaic constituents to the environment. Upon exposure to the natural environment, not even diamonds are forever. In real-world operating conditions, photovoltaics are affected by biodeterioration through biofilm growth that impairs diverse, apparently inert materials, such as rock, glass, and steel. Biodeterioration goes beyond obstructing incoming light and affecting energy conversion; it challenges the physical integrity of substrates. This phenomenon may thus heavily degrade primarily plastic-based thin-film photovoltaics. Following initial degradation, functional layers can undergo microbially mediated dissolution and precipitation, thereby affecting the lifetimes of such solar cells. Biofilm development also influences how potentially harmful photovoltaic constituents (e.g., lead from perovskites) are released to the environment. Despite the considerable potentiality of these detrimental effects, however, they are yet to be systematically studied. Given that different types of solar cells commonly use similar materials, the biodeterioration mechanisms reviewed here may affect several technologies. This paper provides a comprehensive review of the colonization of photovoltaics by sub-aerial biofilms and their potential negative impacts on photovoltaics. We discuss why abiotic laboratory tests for PV efficiency and lifetime poorly reflect the stress PVs suffer in outdoor conditions. We then summarize the knowledge on soiling as well as microbial-, algal-, and fungal growth on PVs. This is followed by a discussion of the physical mechanisms that affect PV efficiency via soiling and photon competition as well as chemical and biological mechanisms (plastic degradation, microbially induced dissolution, and precipitation reactions) that can affect active layers and thus the lifetime of PVs in the field. Solar cells are subjected to various physical, chemical, and biological stressors in the field. Here, a perspective on the potential detrimental effects of biofilm growth on solar cells is given. Soiling and photon competition affect the photovoltaic performance of all cells, while a suite of biochemical mechanisms (“biodeterioration”) may affect the efficiency and lifetime of plastic-based solar cells in particular. Further, biodeterioration might provide a pathway for the entry of harmful solar cell components to the environment.