Potential Improvement in Fill Factor of Lead-Halide Perovskite Solar Cells

In this study, the origin of the fill factor (FF) in lead-halide perovskite solar cells is discussed based on different thicknesses of 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD) as the hole-transporting layer (HTL). As the thickness of HTL is decreased, FF increases and hence, the photovoltaic performance is also improved. This is mainly ascribed to the reduced series resistance with decreasing HTL thickness. Such improvement in FF is examined on the basis of an empirical equation for FF with the diode and photovoltaic parameters. As a result, the thickness-dependent FF can be well explained by this equation. The potential improvements in FF and PCE are further discussed on the basis of the empirical equation.