Efficient solid-state dye-sensitized solar cells were obtained using a small hole transport material, MeO-TPD (N,N,N',N'-tetrakis(4-methoxyphenyl)benzidine), after an initial light soaking treatment. It was discovered that the light soaking treatment for the MeO-TPD based solar cells is essential in order to achieve the high efficiency (4.9%), which outperforms spiro-OMeTAD based solid-state dye-sensitized solar cells using the same dye and device prepn. parameters. A mechanism based on Li+ ion migration is suggested to explain the light soaking effect. It was obsd. that the electron lifetime for the MeO-TPD based solid-state dye-sensitized solar cell strongly increases after the light soaking treatment, which explains the higher efficiency. After the initial light soaking treatment the device efficiency remains considerably stable with only 0.2% decrease after ∼1 mo (unsealed cells stored in dark).