Abstract
Over the past decade perovskite solar cells (PSCs) have quickly established themselves as a promising photovoltaic technology boasting both high efficiency and low processing costs. In recent years, a multitude of highly efficient PSC structures have been demonstrated. Amongst these PSCs prepared using 2,2',7,7'-Tetrakis[N,N-di(4- methoxyphenyl)amino]-9,9'-spirobifluorene as a HTL have stood out for their outstanding performance, enabling power conversion efficiencies (PCEs) beyond 25%. Nevertheless, spiro-OMeTAD suffers from several drawbacks including sub-optimal hole extraction around the open-circuit voltages and accelerated degradation of the PSCs. In this work, these challenges are addressed using a novel organometallocene modification located at the interface between perovskite and spiro-OMeTAD. Photophysical studies conducted on the ferrocene modified interface reveal improvements in the hole extraction yield. Consequently, devices prepared with ferrocene exhibited significantly improved performance reaching PCEs of up to 23.45 % compared to 21.61 % in devices prepared without ferrocene. In addition to improved performance, composition studies reveal reduced diffusion of highly destructive hygroscopic Li+ ions into the perovskite in PSCs prepared with ferrocene. Stability testing on unencapsulated ferrocene prepared devices under high humidity conditions (RH = 60 %) and high temperature (60 oC) stored for > 1,000 hours confirms that the suppressed Li+ diffusion translates to real improvements in device stability, when compared to conventional spiro-OMeTAD devices. The work clearly outlines the merits of introducing organometallocenes at the interface between perovskite and spiro-OMeTAD for both high efficiency and impressive stability.