A fluorene terminated hole transporting material for highly efficient and stable perovskite solar cells
Perovskite solar cells (PSCs) require both high efficiency and good long term stability if they are to be commercialized. It is crucial to finely optimize the energy level matching between the perovskites and hole transporting materials to achieve better performance. Here, we synthesize a fluorene terminated hole transporting material with a fine tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable PSCs. We use this material to fabricate photovoltaic devices with 23.2% efficiency (under reverse scanning) with a steady state efficiency of 22.85% for small area ~0.094 cm2) cells and 21.7% efficiency (under reverse scanning) for large area ~1 cm2) cells. We also achieve certified efficiencies of 22.6% (small area cells, ~0.094 cm2) and 20.9% (large area, ~1 cm2) The resultant device shows better thermal stability than the device with spiro OMeTAD, maintaining almost 95% of its initial performance for more than 500 h after thermal annealing at 60 degC.Interfacial losses between device layers play a key role in determining characteristics of solar cells. Jeon et al. address this in perovskite solar cells by synthesizing a hole transporting layer that is better matched to the surrounding layers, and show high efficiency and high stability devices.