P4891 The impact of oxygen on charge carrier recombination in planar P-I-N perovskite solar cells

Bardo Bruijnaersa, Martijn Wienka, Stefan Meskersa, René Janssena

University of Technology Eindhoven, Den Dolech 2, Eindhoven, 5612, NL

The atmosphere in which perovskite layers are processed strongly affects the photovoltaic performance. Here we produce P-I-N configuration solar cells (ITO/PEDOT:PSS/Perovskite/PCBM/LiF/Al) using a mixture of lead acetate, lead chloride and methylammonium iodide from N,N-dimethylformamide that can be processed completely in air using a hot cast method. We separate the processing into two major components; spin coating and annealing, and compare the photovoltaic performance of layers spin coated in nitrogen and air and annealed in nitrogen and air and show that the spin coating atmosphere has a negligible effect on the photovoltaic performance. The annealing atmosphere, however, is of great influence and annealing in air is necessary to avoid strong charge carrier recombination at high charge carrier densities. We show that the photocurrent increases sublinear with light intensity for cells annealed in nitrogen while the increase is linear for cells annealed in air. By comparing with annealing in dry air or humid nitrogen, we find that it is the oxygen content of the air that is causing the stable performance at higher light intensities. Photoluminescence (PL) measurements show the presence of sub-band gap defects in both types of cells, but the PL intensity of the main emission bands are similar. In electroluminescence (EL), however, there is a clear difference. The EL quantum efficiency of the air annealed sample is higher than that of the nitrogen annealed sample. We propose that this indicates an imbalance in charge carrier injection/transport in the nitrogen annealed cell, also confirming the loss of current at higher light intensity. The same effect is also active in P-I-N solar cells that are produced using the more generally used spin coating at room temperature using the same precursor mixture.