No abstract

The hot carrier solar cell enables the photovoltaic efficiency limit to be approached by tapping into what are normally heat losses. Previous models neglected thermalization in the absorber and assumed ideally energy selective contacts that allow minimum heat losses upon carrier extraction. The proposed improved model includes both realistic contacts and thermalization rates. The heat flux due to carrier extraction is computed. Results show that spectrally broad semiselective contacts are compatible with an efficiency exceeding the single junction limit, which would considerably facilitate the realization of the device.

No abstract

The optimization of functional optical devices requires the appropriate control of light propagation, which can be achieved by using engineered dielectric structures. Innovative materials combination and fabrication strategies are required to achieve a robust gain in performance without impacting manufacturing complexity and cost. In the present work, a novel liquid‐based approach is proposed for the simple and scalable fabrication of highly efficient and robust optical multilayer dielectric coatings. In particular, a sol–gel process is developed that enables the fabrication of large‐area distributed Bragg reflectors (DBR) integrating macroporous materials of controlled closed porosity. The DBRs have a very high index contrast, excellent and tunable optical properties, and high stability of performance and structural integrity with respect to crack formation and delamination, even against harsh ageing tests or solvent exposure. The potential of this approach to be integrated within existing optoelectronic architectures is demonstrated through the integration of a DBR structure as a back reflector in an amorphous silicon solar cell (a‐Si:H), resulting in a significant increase in light absorption, photocurrent, and overall efficiency. This opens the way towards simple dielectric engineering of robust photoactive devices based on the versatile use of liquid routes for the deposition of structured dielectric coatings.

Spontaneous dewetting of a silver layer on a templated silica substrate is proposed as a promising low-cost process to produce self-organized metallic nanostructures. Periodic gratings with inverted pyramid pattern and periods ranging from 200 to 1000 nm are fabricated by nanoimprint on a sol-gel silica layer. A silver layer is then deposited on the templated substrate by magnetron sputtering and annealed to form an array of well-organized islands by solid-state dewetting. The resulting islands are shown to have reduced diameter and size dispersion compared to arrays obtained in the same conditions on flat substrates. The density of defects in the periodic array is determined as a function of silver layer thickness and is lower than 10% in optimal conditions. Optical transmission spectra of periodic arrays are measured, showing extinction peaks that can be related to plasmon resonance. This resonance can be tuned by adjusting the period and particle diameter.

The aim of this work is to produce via a low cost technique a thin film of ZnO showing optoelectronics properties similar to those one could obtain through various vacuum techniques. In order to achieve such goal, electrodeposition appears to be one of the most interesting approaches. Employing such technique in a Cl-containing bath, a high doping of the ZnO layer can be readily achieved through the substitution of a chloride ion for an oxygen atom in the ZnO lattice: the obtained optoelectronic properties are comparable to the ones of vacuum deposited layer. However, the introduction of chloride was found to be difficult to control, leading to a high concentration of inactive chloride in the ZnO lattice and, as a result, lower electrical performances of the material. In this study, the limitation of chloride doping is evidenced and explained considering the formation of chloride rich compounds. Moreover, ab initio calculations demonstrate that incorporation of perchlorate ions in the ZnO lattice at an oxygen site is possible and highlight the efficient doping character of this substitution. Then the influence of the perchlorate ions on the morphological, structural, and optoelectronic properties of electrodeposited ZnO thin films have been experimentally explored. In particular, this study demonstrates that the use of perchlorate as chlorine source prevents the formation of undesirable chlorine rich phases and to reach high doping level and mobility up to 1.7 × 10 20 cm −3 and 19 cm 2 •V −1 •s −1 , respectively.

No abstract

No abstract