Addressing the Challenges of Triplet-Triplet Annihilation In Dye-Sensitized Solar Cells Applications

The transmission of low energy photons is one of the major challenges facing emerging photovoltaics technologies such as dye-sensitized, perovskite and organic solar cells (SCs). This transmission loss could be overcome using some of the third-generation approaches based on “photon-management”. Photon Up-Conversion (UC) and their non-radiative analog, molecular Intermediate Band (IB), are amongst these approaches that could elevate the upper theoretical efficiency limit of a single-junction SC as high as 50 % under non-concentrated sunlight illumination. Although different methods for photon UC do exist, UC based on sensitized triplet-triplet annihilation (sTTA) is of particular interest. This is due to their appreciable UC efficiencies at a relatively low light intensities and in diffuse lighting conditions, which is very appropriate for the real world solar applications. Additionally, they have a relatively strong absorbance, high TTA efficiency, as well as broad absorption range and incoherent nature. To date, a number of high quantum efficiency sTTA-UC systems have been demonstrated, including at non-concentrated solar illumination intensity. These systems are however yet to be successfully translated to high-efficiency photovoltaic devices. This thesis will focus on understanding and overcoming some of the key challenges associated with integrating sTTA-UC with the SCs, such as 1) the underestimation of the photogenerated current response when using the chopped-light external quantum efficiency (EQE) measurements 2) the fact that EQE enhancement values due to the integration of the UC systems are still well below the reported UC quantum yields (QYs) values and 3) the expected quenching of the sTTA-UC due to redox mediators in DSC-UC integrated systems. This thesis aims to understand and provide insight into these limitations and challenges of the UC-assisted and UC-integrated SCs, specifically dye-sensitized SCs (DSCs), as well as providing solutions to overcome them.