Dissertation defence (Materials Engineering): MSc Joaquín Valdez García

MSc (in Materials Science and Engineering) Joaquín Valdez García defends the dissertation in Materials Engineering titled “Lessons learned from combining cellulose films with perovskite solar cells” at the University of Turku on 23 January 2026 at 12.00 (University of Turku, Publicum, Pub1 Mauno Koivisto lecture hall, Assistentinkatu 7, Turku).

Opponent:  Dr. Sjoerd Veenstra (Netherlands Organisation for Applied Scientific Research (TNO), the Netherlands)

Custos: Professor Kati Miettunen (University of Turku)

Summary of the Doctoral Dissertation:

Solar energy is one of the most promising renewable energy sources; however, the increasing production of solar cells raises concerns regarding end-of-life recycling. Among emerging photovoltaic technologies, perovskite solar cells (PSCs) stand out as particularly promising. Owing to their low-temperature and easy fabrication, high efficiencies, and compatibility with printing techniques, PSCs have the potential to be more sustainable than conventional silicon-based devices.

At present, solar panel recycling remains challenging due to the difficulty of separating valuable and hazardous materials from glass substrates and encapsulating resins, making device redesign essential. To address this issue, PSCs must be fabricated using materials that facilitate recycling. Incorporating renewable, biobased materials into solar cell design is therefore crucial, and in a country with abundant forestry resources, paper seems like an obvious choice. In this thesis, I examine the suitability of cellulose films (i.e., transparent paper) as substrate materials for printable solar cells.

Replacing conventional substrates for flexible electronics—such as flexible glass and synthetic polymers including PET and PEN—poses significant challenges. A viable alternative must meet many requirements, including resistance to the solvents used in printed electronics fabrication, thermal stability at temperatures over 100 °C, low thermal expansion, ultra-low surface roughness, high optical transparency, and low permeability to water vapor and oxygen.

This thesis demonstrates how pretreatment of nanocellulose influences the mechanical, morphological, and optical properties of cellulose films, and concludes by establishing a methodology for fabricating and characterizing more sustainable solar cells through the integration of robust cellulose substrates with alternative PSC fabrication approaches. These findings contribute to the advancement of truly renewable and sustainable energy technologies.