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

• TiO2 subwavelength structures (SWSs) are used for antireflection coatings.
• The TiO2 SWSs are fabricated using gold nanopatterns and subsequent dry etching.
• The TiO2 SWSs show wide-angle and broadband antireflective properties.
• The efficiency of III–V GaAs single-junction solar cells with TiO2 SWSs is improved.
• The antireflective TiO2 SWSs are very promising for high-performance solar cells.

The power conversion efficiency (PCE) improvement of III–V gallium arsenide (GaAs) single-junction (SJ) solar cells with titanium dioxide (TiO2) subwavelength structures (SWSs) as antireflection coatings (ARCs) is reported. TiO2 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 (θi) of 3–80°, together with the theoretical prediction by a rigorous coupled-wave analysis. For SWSs on the 50 nm-thick TiO2 layer/GaAs substrate, a lower solar weighted reflectance (SWR) of ~6.2% is obtained compared to that (i.e., SWR ~9.5%) of the TiO2 single-layer ARC (SLARC). By employing the TiO2 SWSs into the III–V GaAs SJ solar cell, the increased short circuit current density (Jsc) of 24.82 mA/cm2 is achieved, thus leading to an improved PCE of 19.66% at θi=0° (i.e., Jsc=18.38 and 23.65 mA/cm2 and PCE=14.74 and 18.98% for the solar cells with bare surface and TiO2 SLARC, respectively). For incident angle-dependent device characteristics, the solar cell with the TiO2 SWSs also exhibits superior performance over a wide θi range of 20–80°. Additionally, after the encapsulation, its Jsc and PCE values are slightly increased to 26.15 mA/cm2 and 20.73%, respectively. For the stability, there are no significant variations in Jsc and PCE after about 50 days.

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