The thermal stability of solar cell materials and interfaces are important prerequisites, as solar cells are often exposed to elevated temperatures during fabrication and operation. Glass transition temperature is a critical parameter that determines the kinetics of molecular reorganization of polymer semiconductors during thermal treatments. Our work includes morphology studied by dynamic mechanical thermal analysis (DMA). Compared to normal DMA measurements the materials are deposited onto a supporting substrate. The technique is a highly sensitive method for determining the Tg of materials, including sub-Tg transitions and melting points.[1]

A completely amorphous indacenodithiophene based polymer was synthesized and used in solar cells combined with the Y6 acceptor material. In contrast to conventional donor:acceptor (D:A) systems, the charge generation is mainly driven by Y6, allowing a high performance even at a low D:A mass ratio of 1:50. Low ratios are generally believed to yield lower efficiency than the more conventional 1:1.2 ratio. However, the solar cells exhibit a peak performance over 11% PCE at a D:A ratio of 1:5.[2] Unexpectedly, as the polymer proportion increases, a reduced photovoltaic performance is observed. Similarly, nanoparticles made of the materials and used for photocatalytic hydrogen evolution show an analogous trend with a peak performance at a D:A ratio of 1:6.7.