Fig. 3. (a) Traditional DSSC use either a thermoplastic or porous insulating spacer to avoid short circuit between the mesoporous TiO₂ and the counter electrode. (b) Type II junction alignment³¹ of the band edges for the mesoporous TiO₂ film and a p-type semiconductor layer. The p-type semiconductor serves as an electron-blocking hole-selective charge collection layer. (c) The sensitized TiO₂ electrode and the PEDOT semiconductor-based counter electrode make direct contact via mechanically pressing and make a new DSSC embodiment. (d) In the DSSC with the contacted electrodes, the redox couple diffuses merely through the mesoscopic TiO₂ film (reproduced from reference with permission²⁵).