Melt-infiltration of spiro-OMeTAD and thermal instability of solid-state dye-sensitized solar cells
A method for achieving complete pore-filling in solid-state dye-sensitized solar cells termed meltinfiltration is presented: after the customary solution-processed deposition of spiro-OMeTAD, the device is heated above the glass transition temperature of spiro-OMeTAD to soften the material and allow capillary action to pull additional spiro-OMeTAD from the overlayer reservoir into the pores. The porefilling fraction increases from 60-65% to 90-100% as a result of melt-infiltration. The organic D-p-A dye used in this study is found to withstand the thermal treatment without performance loss, unlike ruthenium-based dyes. Through our experiments, we find that the 4-tert-butylpyridine (tBP) additive, commonly used in dye-sensitized solar cells, evaporates from the device during heat treatment at temperatures as low as 85 degrees C. This significantly impacts device performance, potentially excluding its use in commercial applications, and demonstrates the need for a more thermally stable tBP alternative. Melt-infiltration is expected to be a viable method for achieving complete pore-filling in systems where volatile additives are not required for operation.