Study of the pore filling fraction of carbazole-based hole-transporting materials in solid-state dye-sensitized solar cells

Abstract : Carbazole-based molecular glasses have emerged as a promising alternative to the widely used hole-transporting materials (HTM) spiro-OMeTAD in solid-state dye-sensitized solar cells (DSSCs). The pore filling fraction (PFF) of the mesoporous TiO2 layer by the HTM appears as a key parameter determining the final efficiency of a DSSC. In this work, the pore-filling properties of a family of carbazole-based HTMs are investigated for the first time and the photovoltaic behavior of DSSC devices (fabricated using the D102 dye) is discussed in light of the present findings. It is found that N-aryl substituted 3,6-bis(diphenylaminyl)-carbazole derivatives exhibit relatively low PFF of ca. 60%. Methoxy groups on the diphenylamine moieties have little influence on the PFF, indicating that the strong enhancement in power conversion efficiency (PCE) is not related to an improved filling of the pores by the HTM. N-alkylated HTMs lead to higher PFF, increasing with the alkyl chain length, up to 78%.