The absorption tail can also be observed in the absorption spectrum of the ns-PLD CIGS thin film. Yet, the tail is much less significant for the ns-PLD CIGS film, presumably due to the fact that the individual radiative defect Luminespib chemical structure energy levels in ns-PLD CIGS film are more concentrated and less fluctuating. The discreteness of the PL emission peaks seen in the PL spectrum of the ns-PLD CIGS films evidently lends strong support to the above conjecture. At room temperature, the ns-PLD CIGS film shows a weaker PL intensity than that of the fs-PLD CIGS, which is due to the higher concentration of non-radiative recombination
centers induced by surface state between CIGS/Cu2 – x Se and CIGS/void interfaces. In addition, the stronger PL intensity of the fs-PLD CIGS can correspond to the existence of the (220)-oriented peak whose higher work function is beneficial for reducing the surface recombination. The results indicate that the fs-PLD CIGS film Combretastatin A4 is much more promising for device performance compared to the ns-PLD CIGS film. Figure 5 PL spectra (a) and fs pump-probe spectra (b) for ns-PLD (blue) and fs-PLD (red) CIGS thin films. The defects in the CIGS thin films can also affect the carrier dynamics, hence their device performance. To this respect, carrier dynamics in CIGS thin films obtained by different PLD processes were investigated by fs pump-probe spectroscopy, which is a technique ubiquitously adopted to delineate the
non-equilibrium carrier dynamics in semiconductors [18, 19]. Figure 5b shows the reflectivity transient in both films with a pumping power of 30.4 μJ/cm2 at room temperature. It is apparent from Figure 5b that the carrier lifetime is much longer in the fs-PLD CIGS film. The defect-related non-radiative recombination lifetime (τ n) can be derived from the results obtained by using different pumping fluences. selleck chemicals It showed that the τ n of ns- and fs-PLD CIGS films are 20 and 30 ps, respectively, revealing that the Shockley-Read-Hall (SRH) mechanism is more dominant in the ns-PLD CIGS
at room temperature because of the existence of CIGS/Cu2 – x Se and CIGS/void interfaces. On the other hand, the longer lifetime in the fs-PLD CIGS suggests less SRH recombination that is consistent with the existence of the (220) orientation. Finally, we examined the electrical selleck compound properties by van der Pauw four-probe measurements. The resistivity values of ns- and fs-PLD CIGS thin films were approximately 66.0 Ω cm and approximately 0.1 Ω cm, respectively. The higher resistivity of the ns-PLD CIGS thin films can be attributed to the higher concentration of non-radiative recombination center verified by PL and pump-probe measurements. The superior carrier transport properties exhibited in the fs-PLD CIGS film again could be attributed to the substantial improvements realized in suppressing the formation of Cu2 – x Se secondary phase and air voids by the fs-PLD process.