Dehydration of molybdenum oxide hole extraction layers via microwave annealing for the improvement of efficiency and lifetime in organic solar cellsElectronic supplementary information (ESI) available: Additional Fig. S1-S8 and Tables S1 and S2. See DOI: 10.1039/c6tc02259f

• Main Authors: Soultati, Anastasia, Kostis, Ioannis, Argitis, Panagiotis, Dimotikali, Dimitra, Kennou, Stella, Gardelis, Spyros, Speliotis, Thanassis, Kontos, Athanassios G, Davazoglou, Dimitris, Vasilopoulou, Maria
• Format: Journal Article
• Published: 11.08.2016
• DOI: 10.1039/c6tc02259f
• ISSN: 2050-7526

A significant contribution to the improvement of efficiency and lifetime of organic solar cells is due to the successful engineering of the metal contact/organic interface by introducing appropriate interlayers. In the current work we show that a short microwave post-annealing treatment in air of an under-stoichiometric molybdenum oxide (MoO x ) hole transport layer significantly enhanced the performance and lifetime of an organic solar cell based on a poly(3-hexylthiophene):[6,6]-phenyl-C 71 -butyric acid methyl ester (P3HT:PC 71 BM) blend. The enhanced performance is mainly driven by improvement in the short circuit current ( J sc ) and the fill factor (FF), caused by, except for an increase of the anode work function, reduced series resistance, and increased shunt resistance and also higher charge generation efficiency, reduced recombination losses and improved hole transport towards the anode contact. In addition, the lifetime of the devices with microwave annealed MoO x interlayers was also significantly improved compared to those with as-deposited MoO x and, especially, those with the PEDOT-PSS interlayer. The above were attributed to effective dehydration which was also followed by structural transformation and crystallization of the MoO x layer during microwave annealing. The removal of absorbed water molecules led to alterations of the structure and microstructure of the MoO x films, visible in the X-ray diffraction patterns, infrared and Raman spectra and atomic force microscopy images recorded on their surface without influencing the oxide's chemical composition as evidenced by X-ray photoelectron spectroscopy. During microwave annealing the substrate remains practically at room temperature, so the method is applicable for films deposited on plastics or other temperature-sensitive substrates. Microwave post-annealing induces effective dehydration in the MoO x hole transport layer and enhances the efficiency and lifetime of organic solar cells.