Organic Photovoltaics for Outdoor and Indoor Applications

Organic Photovoltaics (OPVs) have been actively researched during the past three decades due to their low cost, flexibility, solution processability, and robustness. With the development of novel non-fullerene acceptor (NFA) materials, the power conversion efficiency (PCE) exceeds 18% under the one-sun condition for single-junction devices. However, developing absorber material alone is not enough to advance OPV performance because the opposite type of charge carriers is likely to recombine at the electrodes when the active layer contacts intimately with the anode and cathode. To mitigate the charge carrier recombination, it is critical to developing appropriate interfacial materials to selectively pass the desired charges, i.e., positive ones, while blocking the undesired negative ones. In Chapter 2 of this dissertation, solution-processed Mg doped CuCrO2 nanoparticles have been demonstrated as efficient hole transport layers. Mg doping effects from structural, chemical, morphological, optical, and electronic properties of CuCrO2 are investigated. Under the indoor condition, several high-performance indoor OPVs (IOPVs) have been reported with the highest PCE surpassing 30%. Many groups have studied the light intensity dependence of IOPVs. However, the IOPV performance as a function of color temperature has not been carefully examined before. In Chapter 4 of this dissertation, the PCE as a function of correlated color temperature (CCT) in several organic donor-acceptor systems is studied. Due to the different absorption spectra of organic materials, two groups of behaviors, CCT-independent and CCTdependent, are seen, which provides a guidance on selecting suitable IOPVs for different applications. In Chapter 5 of this dissertation, we focus on understanding the photocurrent generation in OPV devices using two popular commercial NFAs. We show charge transport determines the significant photocurrent difference. Understanding the mechanism behind higher photocurrent is pivotal for developing NFA-based OPVs.