Designing an Ultrathin Film Spectrometer Based on III-Nitride Light-Absorbing Nanostructures

In this paper, a spectrometer design enabling an ultrathin form factor is proposed. Local strain engineering in group III-nitride semiconductor nanostructured light-absorbing elements enables the integration of a large number of photodetectors on the chip exhibiting different absorption cut-off wavelengths. The introduction of a simple cone-shaped back-reflector at the bottom side of the substrate enables a high light-harvesting efficiency design, which also improves the accuracy of spectral reconstruction. The cone-shaped back-reflector can be readily fabricated using mature patterned sapphire substrate processes. Our design was validated via numerical simulations with experimentally measured photodetector responsivities as the input. A light-harvesting efficiency as high as 60% was achieved with five InGaN/GaN multiple quantum wells for the visible wavelengths.

Optical and electronic properties of croconates dye molecules adsorbed on TiO2 brookite nanocluster for dye sensitized solar cells application

Density functional theory simulations were employed to explore the geometric, electronic and optical properties of two croconate dye molecules adsorbed on TiO2 brookite nanocluster. The calculations were based on determination of conjugate length, absorption spectra and light harvesting efficiency. The absorption energies, absorption spectra and electronic states of the dye-TiO2 complex were calculated using TD/DFT. The analysis of the excited state properties shows that CR1 and CR2 showed excitation around 580 nm and 680 nm respectively with a corresponding maximum light harvesting efficiency of 66% and 33.9% for CR1 and CR2 respectively. The absorption wavelength support that the croconate dye molecules can improve the efficiency of DSSCs as they can absorb the near infrared photons which increases the absorption range of DSSCs on the solar spectrum. The adsorption energies of CR1 and CR2 on TiO2 brookite are 3.93 eV and 5.53 eV respectively, suggesting a stable grafting of the dyes onto the surface of the semiconductor. The shifting of the absorption wavelength towards the infrared region upon adsorption gives probability of more electron transport into the large band gap of TiO2.