All-solid-state dye-sensitized solar cells incorporating SWCNTs and crystal growth inhibitor

A solid organic ionic crystal, 1-ethyl-3-methylimidazolium iodide (EMII), was employed as a charge transfer intermediate (CTI) to fabricate all-solid-state dye-sensitized solar cells (DSSCs). In addition, single wall carbon nanotubes (SWCNTs) were incorporated into the CTI as the extended electron transfer materials (EETM), which can reduce charge diffusion length and serve simultaneously as catalyst for the electrochemical reduction of I(3)(-). An all-solid-state DSSC with this hybrid SWCNT-EMII achieved a higher cell efficiency (1.88%), as compared to that containing bare EMII (0.41%). To further improve the cell efficiency, we utilized 1-methyl-3-propylimidazolium iodine (PMII), which acts simultaneously as a co-charge transfer intermediate and crystal growth inhibitor. The binary CTI (EMII mix with PMII) is in the form of solid as the weight percentage of PMII reaches 60%, at which a smoother surface morphology for the binary CTI is observed. The highest cell efficiency (3.49%) was obtained using a hybrid SWCNT-binary CTI. At-rest durability of the DSSC with the hybrid SWCNT-binary CTI was also studied and found to be far superior to that of a cell with an organic solvent electrolyte. Electrochemical impedance spectroscopy (EIS) and laser-induced photo-voltage transient were used to substantiate the results.