Table 3.

Parameters of impedance spectra of DSSCs based on open-ended freestanding TiO₂ nanotube arrays with/without carbon materials and with/without large TiO₂ NPs.

Based on Open-Ended Freestanding TiO2 Nanotube Arrays	Rs (Ω)	R1 (Ω)	CPE1 (F)	R2 (Ω)	CPE2 (F)
Without carbon materials and large TiO2 NPs	10.67	6.16	7.59 × 10−6	56.27	1.99 × 10−3
With carbon materials	10.43	6.23	8.89 × 10−6	37.43	1.94 × 10−3
With large TiO2 NPs	10.40	5.91	7.91 × 10−6	34.26	2.21 × 10−3
With carbon materials and large TiO2 NPs	10.26	5.11	9.86 × 10−6	29.02	2.51 × 10−3

Note: R_s: ohmic series resistance; R₁: sum of small semicircles at high frequency; CPE₁: constant phase element 1; R₂: sum of large semicircles at low frequency; CPE₂: constant phase element 2.