The present invention proposes a method to form a double-graded CdSeTe thin film. The method comprises providing a base substrate, forming a first CdSe.sub.wTe.sub.1-w layer having a first amount w1 of selenium in it, forming a second CdSe.sub.wTe.sub.1-w layer having a second amount w2 of selenium in it and forming a third CdSe.sub.wTe.sub.1-w layer having a third amount w3 of selenium in it. The second amount w2 lies in the range between 0.25 and 0.4, whereas each of the amounts w1 and w3 lies in the range extending from 0 to 1. According to the present invention, the energy gap in the first and the third CdSe.sub.wTe.sub.1-w layers is equal to or higher than 1.45 eV and the energy gap in the second CdSe.sub.wTe.sub.1-w layer lies in the range between 1.38 eV and 1.45 eV and is smaller than the energy gap in the first and the third CdSe.sub.wTe.sub.1-w layers.

Provided are methods for obtaining n-type doped metal chalcogenide quantum dot solid-state films. In some embodiments, the methods include forming an metal chalcogenide quantum dot solid-state film, carrying out a n-doping process on the metal chalcogenide quantum dots of the metal chalcogenide quantum dot solid-state film so that they exhibit intraband absorption, wherein the process includes partially substituting chalcogen atoms by halogen atoms in the metal chalcogenide quantum dots and providing a substance on the plurality of metal chalcogenide quantum dots, to avoid oxygen p-doping of the metal chalcogenide quantum dots. Also provided are optoelectronic devices, which in some embodiments can include an n-type doped metal chalcogenide quantum dot solid-state film (A) obtained by a method as disclosed herein and first (E1) and second (E2) electrodes in physical contact with two respective distanced regions of the film (A).

Photodetectors based on colloidal quantum dots and methods of making the photodetectors are provided. Also provided are methods for doping films of colloidal quantum dots via a solid-state cation exchange method. The photodetectors include multi-band photodetectors composed of two or more rectifying photodiodes stacked in aback-to-back configuration. The doping methods rely on a solid-state cation exchange that employs sacrificial semiconductor nanoparticles as a dopant source for a film of colloidal quantum dots.

The efficiency of a photovoltaic device is enhanced by operating the device in a dark bias mode during a dark period, and in a power generation mode during a subsequent illuminated period. The dark period occurs when an insufficient amount of irradiance is received by the photovoltaic device to produce a useful amount of generated power. In the dark bias mode, a forward DC biasing current is applied to the photovoltaic device, and the device consumes a small current. In the power generation mode, the forward bias is not applied to the photovoltaic device, and the photovoltaic device generates a current in a direction opposite to that of the forward biasing current that was applied during the preceding dark period.

Provided are structures and methods for doping polycrystalline thin film semiconductor materials in photovoltaic devices. Embodiments include methods for forming and treating a photovoltaic semiconductor absorber layer.

Photo-detection device (100) including a semiconductor substrate (110) made of Cd.sub.xHg.sub.1-xTe, with an N-doped region (120), a P-doped region (130), and a concentrated casing (150) only located in the P-doped region and having an average cadmium concentration greater than the average cadmium concentration in the N-doped region.

According to the invention, the concentrated casing (150) has a cadmium concentration gradient, defining therein at least one intermediate gap zone (151) and at least one high gap zone (152), and the intermediate gap zone (151) is in direct physical contact with an electrical contact block (170).

A significant reduction in the dark current and an optimal charge carrier collection are thus combined.

A photovoltaic cell can include an interfacial layer in contact with a semiconductor layer.

A photovoltaic cell can include a dopant in contact with a semiconductor layer.

Described herein is a diffusion-based ex-situ group V element doping method in the CdCl.sub.2 heat-treated polycrystalline CdTe film. The ex-situ doping using group V halides, such as PCl.sub.3, AsCl.sub.3, SbCl.sub.3, or BiCl.sub.3, demonstrated a promising PCE of ˜18% and long-term light soaking stability in CdSe/CdTe and CdS/CdTe devices with decent carrier concentration>10.sup.15 cm.sup.−3. This ex-situ solution or vapor process can provide a low-cost alternative pathway for effective doping of As, as well as P, Sb, and Bi, in CdTe solar cells with limited deviation from the current CdTe manufacturing process.

Provided are structures and methods for doping polycrystalline thin film semiconductor materials in photovoltaic devices. Embodiments include methods for forming and treating a photovoltaic semiconductor absorber layer.