Precursor solution of CH3NH3PbI3-xClx for perovskite solar cells was conventionally prepared by mixing PbCl2 and CH3NH3I with a mole ratio of 1:3 (PbCl2:CH3NH3I). While in the present study, CH3NH3PbI3-xClx-based solar cells were fabricated using the precursor solutions containing PbCl2 and CH3NH3I with the mole ratios of 1:3, 1.05:3, 1.1:3, and 1.15:3, respectively. The results display that the solar cells with the mole ratio of 1.1:3 present higher power conversion efficiency and less I-V hysteresis than those with the mole ratio of 1:3. Based on some investigations, it is concluded that the higher efficiency could be due to the smooth and pinhole free film formation, high optical absorption, suitable energy band gap, and the large electron transfer efficiency, and the less I-V hysteresis may be attributed to the small low frequency capacitance of the device.

The surface‐enhanced Raman scattering (SERS) of molecules on TiO2 (Degussa P25) was investigated. The variation of trap density was carried out by the calcination of TiO2 at 350, 450 and 600°C. We found that the SERS intensity increases first, and then decreases with the calcination temperature rising from 350 to 450°C and 450 to 600°C, respectively. The measurements indicate that the trap density increases with the calcination temperature rising. The results indicate that the increase of trap density is favorable for the increase of SERS enhancement. The increase of SERS intensity from 350 to 450°C could be due to the dominated contribution from the trap density increase, and the decrease from 450 to 600°C could be due to dominated contribution from the increase of the crystallite size and the mass fraction of rutile phase. Copyright © 2012 John Wiley & Sons, Ltd.

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