**8. Summary**

352 Solar Cells – New Aspects and Solutions

ZnO thin film was prepared by RF sputtering of 99.999% pure ZnO target (Kurt J. Lesker, PA, diameter 2 inches and thickness 0.25 inches). ZnO intrinsic film was deposited by RF power of 100 W at 0.7 Å/s and subsequently annealed in air at 150 0C. ITO film was also prepared from 99.99% pure ITO target (Kurt J. Lesker, PA, diameter 2 inches and thickness 0.25 inches) on the similar fashion using dc magnetron sputtering. Transparent ITO film was deposited at plasma pressure of 4.5 mTorr. The sputtering power of 20 W yields deposition rate 0.3 Å/s. The film was then annealed at 150 0C in air for 1 hour. The highly ordered mesoporous TiO2 was deposited by sol gel technique as described by Tian et al. (Tian et al. 2005). CuSCN thin film was prepared by spin coating the saturated solution of CuSCN in dipropyl sulphide and dried in vacuum oven at 80 0C (Li et al., 2011). The thickness of all three films ZnO, ITO and TiO2 film was about 100 nm and the thickness of AlSb layer is ~1

Current voltage measurement of the solar cells was carried out using Agilent 4155c (Agilent, Santa Clara, CA) semiconductor parameter analyzer equipped with solar cell simulator in SDSU. Fig. 10 shows the experimental set up used for measuring I-V response of the solar cells, where 2 SMUs (source measurement unit) were used. The SMU s could operate as a voltage source (constant sweep voltage) or a current source and it could measure voltage and current at the same time. The SMUs could measure from 10-12 A to 1 A and -10 V to 10 V. SMU 1 was set as voltage sweep mode from -1 V to 1 V with steps of 0.01 V, and SMU 2 was set to measure current of the solar cell during IV measurement. IV responses were measured under both dark and illuminated condition. During illumination, the intensity of the simulated light

was 100 mW·cm-2 and calibrated using the NREL calibrated standard cell.

Fig. 10. Experimental set up for measuring IV response of a solar cell.

Table 3 shows the current voltage characteristics of p-n junction solar cells with structures AlSb/TiO2, AlSb/ZnO. The active cell area was 0.16 cm2 and fabricated on ITO coated glass

The *V*oc of the best cell with ZnO as an n type layer was found out to be 120 mV and *I*sc to be 76 uA. The *FF* of the cell was calculated to be 0.24 and the efficiency was 0.009%. The cell with TiO2 as an n layer has even lower *V*OC and *I*sc. TiO2 is less suitable n-type layer for making junction with AlSb than ZnO because it is far more conductive than TiO2. A number of reasons may be attributed for this low efficiency. First, is due to small electric field at the junction between AlSb and the n type material (ZnO or TiO2). This severely limits the charge

micron. The active layer was annealed.

**7. I-V Characterization of solar cell** 

surface.

AlSb thin film has been prepared by co-sputtering aluminum and antimony. The deposition rate of Al:Sb was required to be 3:7 to produce the stoichiometric AlSb film with optical band gap of 1.44 eV. After annealing the film at 200 0C in vacuum for two hours, the film likely formed crystalline structures with a size of ~200 nm and has strong absorption coefficient in the range of 105 cm-1 in the visible light. p-n and p-*i*-n heterojunction solar cells were designed and fabricated with AlSb as a p-type material and an intrinsic absorber layer. The simulation of the p-i-n junction solar cell with CuSCN/AlSb/ZnO using AMPS at AM1.5 illumination shows efficiency of 14% when setting ~1 m-thick absorber layer. The p-n junction solar cells were fabricated with different types of n layers shows the photovoltaic responses. The p-*i*-n showed better photovoltaic performance than that of p-n junction cells. All the preliminary results have demonstrated that AlSb is promising photovoltaic material. This work is at the early stage. More experiment is needed for the understanding of the crystallization and properties of the AlSb films and the interface behaviors in the junctions.
