Progress and Future Prospects of Wide-Bandgap Metal-Compound-Based Passivating Contacts for Silicon Solar Cells.

Advanced doped-silicon-layer-based passivating contacts have boosted the power conversion efficiency (PCE) of single-junction crystalline silicon (c-Si) solar cells to over 26%. However, the inevitable parasitic light absorption of the doped silicon layers impedes further PCE improvement. To this end, alternative passivating contacts based on wide-bandgap metal compounds (so-called dopant-free passivating contacts (DFPCs)) have attracted great attention, thanks to their potential merits in terms of parasitic absorption loss, ease-of-deposition, and cost. Intensive research activity has surrounded this topic with significant progress made in recent years. Various electron-selective and hole-selective contacts based on metal compounds have been successfully developed, and a champion PCE of 23.5% has been achieved for a c-Si solar cell with a MoOx -based hole-selective contact. In this work, the fundamentals and development status of DFPCs are reviewed and the challenges and potential solutions for enhancing the carrier selectivity of DFPCs are discussed. Based on comprehensive and in-depth analysis and simulations, the improvement strategies and future prospects for DFPCs design and device implementation are pointed out. By tuning the carrier concentration of the metal compound and the work function of the capping transparent electrode, high PCEs over 26% can be achieved for c-Si solar cells with DFPCs.

A Highly Conductive Titanium Oxynitride Electron-Selective Contact for Efficient Photovoltaic Devices.

High-quality carrier-selective contacts with suitable electronic properties are a prerequisite for photovoltaic devices with high power conversion efficiency (PCE). In this work, an efficient electron-selective contact, titanium oxynitride (TiOx Ny ), is developed for crystalline silicon (c-Si) and organic photovoltaic devices. Atomic-layer-deposited TiOx Ny is demonstrated to be highly conductive with a proper work function (4.3 eV) and a wide bandgap (3.4 eV). Thin TiOx Ny films simultaneously provide a moderate surface passivation and enable a low contact resistivity on c-Si surfaces. By implementation of an optimal TiOx Ny -based contact, a state-of-the-art PCE of 22.3% is achieved for a c-Si solar cell featuring a full-area dopant-free electron-selective contact. Simultaneously, conductive TiOx Ny is proven to be an efficient electron-transport layer for organic photovoltaic (OPV) devices. A remarkably high PCE of 17.02% is achieved for an OPV device with an electron-transport TiOx Ny layer, which is superior to conventional ZnO-based devices with a PCE of 16.10%. Atomic-layer-deposited TiOx Ny ETL on a large area with a high uniformity may help accelerate the commercialization of emerging solar technologies.

High-Performance TiO2 -Based Electron-Selective Contacts for Crystalline Silicon Solar Cells.

Thin TiO2 films are demonstrated to be an excellent electron-selective contact for crystalline silicon solar cells. An efficiency of 21.6% is achieved for crystalline silicon solar cells featuring a full-area TiO2 -based electron-selective contact.

Design of ultrabroadband internal reflection gratings with high efficiency.

A high-efficiency, ultrabroadband dielectric internal reflection grating with rhombus-shaped grooves is designed by a rigorous coupled-wave analysis, and an effective method for predicting spectral bandwidths of gratings from their efficiency maps is presented. The grating can be fabricated from a single dielectric material, and its reflection diffraction efficiency of the -1st order can reach more than 0.99. More importantly, an ultrabroadband top-hat diffraction spectrum with efficiency exceeding 0.98 over 170 nm wavelength wide is achieved, which makes the gratings suitable for applications associated with broadband illumination, such as ultrashort pulses.

Design of rectangular-groove fused-silica gratings as polarizing beam splitters.

The application of rectangular-groove fused-silica gratings as polarizing beam splitters (PBSs) under Littrow incidence is investigated. Based on the simple modal method, two different cases of PBS gratings are designed. The achieved solutions, which are independent on the incident wavelength, are verified by the rigorous coupled-wave analysis and expressed in several polynomials instead of listing one or two numerical solutions. More importantly, on the basis of the designed PBS gratings, a porous fused silica antireflective film is introduced to improve their performances. Theoretical results indicate that such modified rectangular-groove PBS gratings exhibit higher diffraction efficiencies (over 0.99) and larger spectral bandwidths.

Translational-symmetry alternating phase shifting mask grating mark used in a linear measurement model of lithographic projection lens aberrations.

A linear measurement model of lithographic projection lens aberrations is studied numerically based on the Hopkins theory of partially-coherent imaging and positive resist optical lithography (PROLITH) simulation. In this linearity model, the correlation between the mark's structure and its sensitivities to aberrations is analyzed. A method to design a mark with high sensitivity is proved and declared. By use of this method, a translational-symmetry alternating phase shifting mask (Alt-PSM) grating mark is redesigned with all of the even orders, +/-3rd and +/-5th order diffraction light missing. In the evaluation simulation, the measurement accuracies of aberrations prove to be enhanced apparently by use of the redesigned mark instead of the old ones.