Efficiency improvement of III-V GaAs solar cells using biomimetic TiO2 subwavelength structures with wide-angle and broadband antireflection properties

Abstract The power conversion efficiency (PCE) improvement of III–V gallium arsenide (GaAs) single-junction (SJ) solar cells with titanium dioxide (TiO 2 ) subwavelength structures (SWSs) as antireflection coatings (ARCs) is reported. TiO 2 SWSs are fabricated by dry etching using dotted gold nanopatterns prepared with glancing angle deposition and thermal dewetting processes. Their optical reflection properties are studied in the wavelength range of 350–900 nm at incident light angles ( θ i ) of 3–80°, together with the theoretical prediction by a rigorous coupled-wave analysis. For SWSs on the 50 nm-thick TiO 2 layer/GaAs substrate, a lower solar weighted reflectance (SWR) of ~6.2% is obtained compared to that (i.e., SWR ~9.5%) of the TiO 2 single-layer ARC (SLARC). By employing the TiO 2 SWSs into the III–V GaAs SJ solar cell, the increased short circuit current density ( J sc ) of 24.82 mA/cm 2 is achieved, thus leading to an improved PCE of 19.66% at θ i =0° (i.e., J sc =18.38 and 23.65 mA/cm 2 and PCE=14.74 and 18.98% for the solar cells with bare surface and TiO 2 SLARC, respectively). For incident angle-dependent device characteristics, the solar cell with the TiO 2 SWSs also exhibits superior performance over a wide θ i range of 20–80°. Additionally, after the encapsulation, its J sc and PCE values are slightly increased to 26.15 mA/cm 2 and 20.73%, respectively. For the stability, there are no significant variations in J sc and PCE after about 50 days.