The atomic force microscopy (AFM) see more measurements were performed using an Agilent 5500 AFM (Agilent Technologies, Chandler, AZ, USA). Field emission transmission electron microscopy (FETEM; Model Fei Nova 230, FEI VX 770 Company, Hillsboro, OR, USA) measurements were carried out by scratching a portion of the CdS/TiO2 sample, followed by ultrasonication for a few minutes. Then, a drop of ethanol was placed on a copper grid and subjected to high-resolution transmission electron microscopy (HRTEM). Transmission electron microscopy (TEM) analyses were carried out
on a Tecnai G2 F30 TEM (FEI Company, Hillsboro, OR, USA). The crystalline phase and structure of the as-prepared ITO/nc-TiO2/CdS film were confirmed by power X-ray diffractometry (XRD; DX-2500; Dandong Fangyuan Instrument Co., Ltd., Dandong, China). Current density-voltage (I-V) characteristics of the as-prepared devices were measured using a Keithley 2410 source meter (Cleveland, OH, USA) in the dark and under the illumination of AM 1.5G simulated solar light (100 mW/cm2) provided by a solar simulator (Newport Inc., Irvine, CA, USA). Results and discussion Figure 2a shows the AFM topography image of the ITO/nc-TiO2 thin film. To show the nc-TiO2 film on the ITO glass substrate more clearly, the corresponding AFM phase image of the ITO/nc-TiO2 thin film is shown in Figure 2b.
It can be seen that the TiO2 nanoparticles are Eltanexor cell line distributed uniformly on the ITO glass, and the size of single particle is between 20 nm and 50 nm, which is consistent with the average size (25 nm) of P25 TiO2 nanoparticles. The root-mean-square (rms) surface roughness value of the ITO/nc-TiO2 for 0.5 × 0.5 μm2 is about 12 nm (Figure 2a). Figure 2 AFM images of the films. (a) The AFM topography image and (b) the corresponding AFM phase image of the ITO/nc-TiO2 film. The AFM topography images of (c) the ITO/nc-TiO2/CdS(5) film and (d) the ITO/nc-TiO2/CdS(15) film.
Figure 2c shows the AFM topography image of the ITO/nc-TiO2/CdS(5) thin film. The CdS nanoparticles can be Methocarbamol clearly found in Figure 2c, and the dense CdS nanocrystalline film has been formed. The roughness of the ITO/nc-TiO2/CdS(5) thin film for 0.5 × 0.5 μm2 is about 48 nm, which is much higher than that of the TiO2 nanocrystalline film, suggesting that the introduction of CdS nanoparticles may lead to a more larger interfacial area between the electron donor and acceptor. In our case, the increased roughness of the ITO/nc-TiO2/CdS/P3HT:PCBM film may provide an increased interface area between the P3HT and TiO2 or CdS compared to the ITO/nc-TiO2/P3HT:PCBM film without CdS, which obviously would increase the interfacial dissociation probability of photogenerated excitons at the P3HT/CdS and P3HT/TiO2 interfaces and thereby increase the photocurrent density of the cells [24].