Publication date: 1st July 2014
Recently, the organic/inorganic hybrid solar cells using organic hole conductors and CH3NH3PbX3 (X = halides) on nanocrystalline-TiO2 layers have received a lot of attention due to the applicable conversion efficiency (15%). Because of the organic hole conductor, however, the material price can be extremely high. In this paper, therefore, we have fabricated solar cells using only inorganic (no double bond) printed materials: TiO2, CuSCN and CH3NH3PbI3. In this paper, a new deposition method of CH3NH3PbI3 layer has been investigated. Several structures of inorganic printed solar cells have been fabricated: <glass/FTO/bl-TiO2/ nanocrystalline-TiO2/CH3NH3PbI3/CuSCN/Au> and <glass/FTO/bl-TiO2/CH3NH3PbI3/CuSCN/Au>. In one spin coating procedure, a precursor solution of PbI2 (1.3 M) and MAI (50mg/mL) in DMF and DMSO (9:1 volume ratio) and a solution of MAI (dissolved in 2-propanol, 10mg/mL) were coated on TiO2 electrodes, successively. The resulting layers were annealed at 100 ˚C for 15 minute to be solar cells. Figure 2. SEM surface images of 2-steps process lead-halide perovskite (a) and dripping process lead-halide perovskite (b). Figure 1. Current-voltage characteristics of the heterojunction solar cells with (black and red) and without (green) mp-TiO2 measured under 100mWcm-2.Red line shows 2-steps process lead-halide perovskite. Red and Green lines show dripping process lead-halide perovskite. The best photovoltaic characteristics were performed by a printed solar cells of <glass/FTO/bl-TiO2/ nanocrystalline-TiO2 /CH3NH3PbI3(dripping)/ CuSCN/Au>, which were 18.41 mA cm-2 of the short-circuit current density, 0.97 V of the open-circuit voltage, of 0.64 of the fill factors, and 11.3% of the conversion efficiency (Fig. 1). Since the conversion efficiency of perovskite solar cells on flat-TiO2 by 2-steps method was almost zero (data will be shown in conference), the<glass/FTO/bl-TiO2 /CH3NH3PbI3(dripping)/ CuSCN/Au> cell performed 7.0% conversion efficiency. The lead-halide perovskite crystal diameter by dripping process became larger than that by 2-steps process (Fig. 2), which may be the significance for the photovoltaic effects.