They can be attributed to the enhanced light absorption caused by the multiple photon scattering phenomena associated with the nanorod arrays. According ACP-196 mouse to the weighted reflectance R w [23] with both the internal spectral ABT-737 in vivo response of the solar cell and the AM1.5 solar spectrum, we found that decreasing the nanorod tip diameter to 50 nm improved the R w from 13.5% to 12.6% in the letter. According to the effective medium theory [28], the effective refractive index increases with the filling factor. The filling factors at the air-ZnO nanorod array interface are statistically estimated to be 17.21% and 12.47%

for flat-top and tapered ZnO, respectively. Consequently, tapered ZnO nanorod arrays have the lowest effective refractive index at the interface. Table 1 lists the electrical parameters for all CIGS devices with tapered ZnO nanorod coating. Several concentrations of DAP were also added

to control the tip diameter of tapered nanorods. Six as-fabricated CIGS solar cells prepared from the same batch presented the conversion efficiency and current density of approximate 9.1% and 22.7 mA/cm2, respectively. After covering with 20-nm-diameter ZnO nanorod on the top of solar devices, the efficiency and current density were improved to 11.1% and 29.5 mA/cm2, respectively. This photocurrent increase, related to the increase of photon excitation in the CIGS absorber, enhanced photovoltaic efficiency after introducing ZnO nanorod antireflection coatings. However, the performances of CIGS 4EGI-1 in vitro solar cells were not further enhanced according to further weighted reflectance reduction in other samples.

The tapered ZnO nanorod tip diameter has been varied to find out the optimum diameter for the conventional non-selenized CIGS structure with ZnO nanorod as the antireflection coatings. It has been found that the efficiency of the solar cell is increasing with the decreasing of the tip diameter of the ZnO nanorod, but with a much slower rate under 30 nm. The optimum diameter for ZnO nanorod would be around 20 to 30 nm. Table 1 Photovoltaic performance of non-selenized CIGS solar cells with different conditions of ZnO nanorod antireflection coating Device Tapered ZnO nanorods Electrical properties ID (diameter, nm) Voc (mV) FF (%) Jsc (mA/cm2) η(%) Glycogen branching enzyme Improvement (η, %) Rw (%) 1 – 553 72.3 22.7 9.1   25.1 2 50 551 72.2 25.2 10.0 +9.8 12.6 3 40 552 72.2 26.9 10.7 +17.5 9.6 4 30 552 70.1 28.5 11.0 +20.8 9.1 5 20 553 68.4 29.4 11.1 +21.9 9.1 6 15 553 68.4 29.5 11.1 +21.9 9.0 Conclusions In summary, the effects of ZnO nanorods as a subwavelength-textured antireflection coating on non-selenized CIGS thin-film solar cell have been demonstrated in this work. Based on the moth-eye effect, the reflection on the surface of CIGS solar cell covered with nanostructured ZnO layer can be effectively eliminated.