Angular dependence of light trapping in In0.3Ga0.7As/GaAs quantum-well solar cells

Abstract

The dependence of light trapping effects in In0.3Ga0.7As/GaAs quantum-well solar cells on wavelength and incident angle is experimentally characterized and analyzed. Separation of active device layers from their epitaxial growth substrate enables integration of thin-film semiconductor device layers with nanostructured metal/dielectric rear contacts to increase optical absorption via coupling to both Fabry-Perot resonances and guided lateral propagation modes in the semiconductor. The roles of Fabry-Perot resonances and coupling to guided modes are analyzed via photocurrent response measurements and numerical modeling for light incident at angles of 0° (normal incidence) to 30° off normal. Light trapping enables external quantum efficiency at long wavelengths as high as 2.9% per quantum well to be achieved experimentally, substantially exceeding the ∼1% per quantum well level typically observed. Increased long wavelength quantum efficiency is shown in experimental measurements to persist with increasing angle of incidence and is explained as a consequence of the large number of guided modes available in the device structure.

Subwavelength nanostructures integrated with polymer‐packaged iii–v solar cells for omnidirectional, broad‐spectrum improvement of photovoltaic performance

“…We employ Al 2 O 3 nanoislands for this purpose, examining first the effects of the nanoisland structure without PET packaging sheets. Figure a shows schematic diagrams of the GaAs single‐junction solar cell deposited with conventional Al 2 O 3 /TiO 2 thin‐film bilayer antireflection coating with (i) and without (ii) the additional Al 2 O 3 nanoisland structure . Figure b shows the numerically simulated absorption of structure (i) as a function of wavelength and periodicity ( D 2 ) for θ = 0° and 80°.…”

“…Two key elements are integrated within the final packaged structure—a moth‐eye textured polyethylene terephthalate (PET) packaging sheet, and Al 2 O 3 nanoislands on a single‐junction GaAs solar cell with conventional Al 2 O 3 /TiO 2 bilayer antireflection coating. A rapid, large‐area nanosphere lithography process is employed to create both the moth‐eye nanostructures on PET packaging sheets and Al 2 O 3 nanoislands on Al 2 O 3 /TiO 2 antireflection coatings. Experimental studies of moth‐eye nanostructures on PET reveal the optimal height of the nano‐textured structure which provides the best transmittance performance over the entire wavelength range and incident angles ranging from 0° to 75°.…”

Optical characterization of double-side-textured silicon wafer based on photonic nanostructures for thin-wafer crystalline silicon solar cells

“…11,12) In addition, electromagnetic phenomena such as nano-optic cavities and photonic crystals have been investigated to enhance the absorption in the subwavelength regime. 13,14) Several fabrication methods to obtain efficient light trapping have been demonstrated, including colloidal lithography, 15,16) electron beam lithography, 17) and self-assembly. 18,19) We previously demonstrated a technique to form photonic nanostructures via simple maskless wet etching of Ge quantum dot (QD) multilayers on c-Si solar cells.…”

Minimized open-circuit voltage reduction in GaAs/InGaAs quantum well solar cells with bandgap-engineered graded quantum well depths

“…Additional details regarding the thin-film device fabrication process used in this work have been reported elsewhere. 20,24 The key idea for the graded QW cell structure design is that it enables increased separation of the electron QFL from the QW conduction band-edge at forward bias, resulting in a reduced photo-generated carrier concentration in the QWs at forward bias and, consequently, increased V oc and operating voltage for maximum power output. At the same time, for the graded QW cell structure, the QW barriers can be substantially thinner, compared to those in reference QW cells with the same maximum In content, while remaining below the critical thickness for strain relaxation so that tunneling transport of carriers is facilitated.…”