Influence of Materials and Aging Test Design on Dye Solar Cell Stability

Dye solar cells are an emerging third-generation photovoltaic technology. Its main advantages are the low cost of materials and manufacturing, and the possibility to adjust the colour of the cell by selecting different dyes. Currently one of the main obstacles for commercialisation of dye solar cells is their relatively short lifetime. Silicon solar panels are often given guarantees of over two decades, while dye solar cells can reliably function only for a few years in outdoor conditions. This work focuses on dye solar cell stability from multiple perspectives: the impact of different materials and structures, effect of operating conditions to the cell lifetime, and analysis of the methods used for studying dye solar cell stability. A practical challenge in the production of robust and large dye solar cells is reliably sealing its liquid electrolyte within the cell. It was discovered that soaking a nanocellulose or nanochitin membrane in an electrolyte solution and then sealing it inside the dye solar cell not only simplifies the assembly process, but also increases the initial energy conversion efficiency of the solar cells. Research for improved dye solar cell lifetime can be supported studying how operating conditions affect it, i.e. what kind of factors and mechanisms are most detrimental to stability and should always be taken into consideration in cell design. Since a dye solar cell can function for some years in standard operation, stability studies generally rely on accelerated tests. One focus of this thesis was to study how well approximations made in accelerated tests correspond to realistic conditions. A common mistake in dye solar cell stability testing is to underestimate the degrading effects of UV light. It was found that even a UV filter is inadequate to protect dye solar cells fully, suggesting that UV degradation of dye solar cells is still an issue requiring further research. Another topic that is discussed is how the circuit state of the cells impacts their degradation rate. When solar cells are operating in practice, they are connected to an electric load that brings them close to their maximum power point. Often this is overlooked in research and dye solar cells are aged in open circuit conditions, which may artificially lengthen the lifetime of dye solar cells. This thesis demonstrates that the difference between the two states is small. The work also includes pioneering aging tests in harsh northern conditions. The stability research practices in the field of emerging photovoltaics was reviewed, providing suggestions on how to improve the corresponding research to obtain more accurate results.