Impact of Glass Formation on the Thermal Stability of Non-Fullerene Solar Cells

Licentiate thesis, 2020

As the world faces major challenges with the climate change and the depletion of non-renewable resources, development of renewable sources is crucial towards a more sustainable future. Organic solar cell is an excellent alternative as a renewable resource with many advantages. In contrast to conventional inorganic solar cells organic solar cells can be produced with printing techniques. Making up-scaling of the production possible, which reduces the price. In addition, organic solar cells are lightweight, flexible and semi-transparent. One drawback is the stability of organic solar cells which needs to be improved to achieve longer lifetime and higher durability. 

The aim of this thesis is to investigate the use of multicomponent mixtures to improve the thermal stability of organic solar cells. The first part of the thesis explores the relation between entropy of mixing and glass formation. Perylene molecules with varying sidechains were mixed and it was found that mixing increases the glass formation, especially at low cooling rates where dimers where formed in the mixture. In the last part of the thesis, this mixing concept was used for organic solar cells. Binary devices of PTB7-Th: ITIC-4F and PTB7-Th: ITIC-4Cl were compared with the corresponding ternary solar cell PTB7-Th: ITIC-4F: ITIC-4Cl.  It was found that the crystals were suppressed in the ternary resulting in stable photovoltaic performance up to 170 ºC and in addition stable performance at 130 ºC for more than 200 h, while binary devices suffer crystallization in the active layer.