One-Dimensional Crystal-Structure Te-Se Alloy for Flexible Shortwave Infrared Photodetector and Imaging.

Flexible shortwave infrared detectors play a crucial role in wearable devices, bioimaging, automatic control, etc. Commercial shortwave infrared detectors face challenges in achieving flexibility due to the high fabrication temperature and rigid material properties. Herein, we develop a high-performance flexible Te0.7Se0.3 photodetector, resulting from the unique 1D crystal structure and small elastic modulus of Te-Se alloying. The flexible photodetector exhibits a broad-spectrum response ranging from 365 to 1650 nm, a fast response time of 6 µs, a broad linear dynamic range of 76 dB, and a specific detectivity of 4.8 × 1010 Jones at room temperature. The responsivity of the flexible detector remains at 93% of its initial value after bending with a small curvature of 3 mm. Based on the optimized flexible detector, we demonstrate its application in shortwave infrared imaging. These results showcase the great potential of Te0.7Se0.3 photodetectors for flexible electronics.

Tex Se1-x Photodiode Shortwave Infrared Detection and Imaging.

Short-wave infrared detectors are increasingly important in the fields of autonomous driving, food safety, disease diagnosis, and scientific research. However, mature short-wave infrared cameras such as InGaAs have the disadvantage of complex heterogeneous integration with complementary metal-oxide-semiconductor (CMOS) readout circuits, leading to high cost and low imaging resolution. Herein, a low-cost, high-performance, and high-stability Tex Se1- x short-wave infrared photodiode detector is reported. The Tex Se1- x thin film is fabricated through CMOS-compatible low-temperature evaporation and post-annealing process, showcasing the potential of direct integration on the readout circuit. The device demonstrates a broad-spectrum response of 300-1600 nm, a room-temperature specific detectivity of 1.0 × 1010 Jones, a -3 dB bandwidth up to 116 kHz, and a linear dynamic range of over 55 dB, achieving the fastest response among Te-based photodiode devices and a dark current density 7 orders of magnitude smaller than Te-based photoconductive and field-effect transistor devices. With a simple Si3 N4 packaging, the detector shows high electric stability and thermal stability, meeting the requirements for vehicular applications. Based on the optimized Tex Se1- x photodiode detector, the applications in material identification and masking imaging is demonstrated. This work paves a new way for CMOS-compatible infrared imaging chips.

Improved Carrier Lifetimes of CdSe Thin Film via Te Doping for Photovoltaic Application.

Cadmium selenide (CdSe) solar cells have proven to be a remarkable potential top cell for a silicon-based tandem application. However, the defects and short carrier lifetimes of CdSe thin films greatly limit the solar cell performance. In this work, a Te-doped strategy is proposed to passivate the Se vacancy defects and increase the carrier lifetime of the CdSe thin film. The theoretical calculation helps to reveal the mechanism of nonradiative recombination of the CdSe thin film in depth. After Te-doping, the calculated capture coefficient of CdSe can be reduced from 4.61 × 10-8 cm3 s-1 to 2.32 × 10-9 cm3 s-1. Meanwhile, the carrier lifetime of CdSe thin film is increased nearly 3-fold from 0.53 to 1.43 ns. Finally, the efficiency of the Cd(Se,Te) solar cell is improved to 4.11%, about a relative 36.5% improvement compared to the pure CdSe solar cell. Both theoretical calculations and experiments prove that Te can effectively passivate bulk defects and improve the carrier lifetime of CdSe thin films, deserving further exploration to improve solar cell performance.

Stable Indium Tin Oxide with High Mobility.

Indium tin oxide (ITO) is widely used in a variety of optoelectronic devices, occupying a huge market share of $1.7 billion. However, traditional preparation methods such as magnetron sputtering limit the further development of ITO in terms of high preparation temperature (>350 °C) and low mobility (∼30 cm2 V-1 s-1). Herein, we develop an adjustable process to obtain high-mobility ITO with both appropriate conductivity and infrared transparency at room temperature by a reactive plasma deposition (RPD) system, which has many significant advantages including low-ion damage, low deposition temperature, large-area deposition, and high throughput. By optimizing the oxygen flow during the RPD process, ITO films with a high mobility of 62.1 cm2 V-1 s-1 and a high average transparency of 89.7% at 800-2500 nm are achieved. Furthermore, the deposited ITO films present a smooth surface with a small roughness of 0.3 nm. The stability of ITO films to heat, humidity, radiation, and alkali environments is also investigated with carrier mobility average changes of 19.3, 4.4, and 4.7%, showcasing strong environmental adaptability. We believe that stable ITO films with high mobility prepared by a low-damage deposition method will be widely used in full spectral optoelectronic applications, such as tandem solar cells, infrared photodetectors, light-emitting diodes, etc.

Efficient Near-Infrared PbS Quantum Dot Solar Cells Employing Hydrogenated In2 O3 Transparent Electrode.

Infrared solar cells are regarded as candidates for expanding the solar spectrum of c-Si cells, and the window electrodes are usually transparent conductive oxide (TCO) such as widely used indium tin oxide material. However, due to the low transmittance of the TCO in the near-infrared region, most near-infrared light cannot penetrate the electrode and be absorbed by the active layer. Here, the propose a simple procedure to fabricate the window materials with high near-infrared transmittance and high electrical conductivity, namely the hydrogen-doped indium oxide (IHO) films prepared by room temperature magnetron sputtering. The low-temperature annealed IHO conductive electrodes exhibit high mobility of 98 cm2 V-1 s-1 and high infrared transmittance of 85.2% at 1300 nm, which endows the lead quantum dot infrared solar cell with an improved short-circuit current density of 37.2 mA cm-2 and external quantum efficiency of 70.22% at 1280 nm. The proposed preparation process is simple and compatible with existing production lines, which gifts the IHO transparent conductive film great potential in broad applications that simultaneously require high infrared transmittance and high conductivity.

Rapid thermal annealing process for Se thin-film solar cells.

Recently, selenium (Se) has regained interest as a possible wide-bandgap photovoltaic material for silicon-based tandem applications. However, the easy sublimation of Se below the melting point (220 °C) brings challenges for high-quality Se thin films. Herein, we design a rapid thermal annealing (RTA) method to balance the contradiction between the sublimation and crystallization of Se thin films. Through optimizing the annealing temperature, a high-quality Se thin film is obtained with a large grain size (∼1 µm) and preferred [003] orientation during the RTA process. Then, an optimized efficiency of 3.22% is achieved in a ZnO/Se heterojunction solar cell. This study provides a new guide to obtain high-quality Se thin film by RTA and the method can be extended to other materials with high saturated vapor pressure.

Fabrication and characterization of ZnO/Se1-xTex solar cells.

Selenium (Se) element is a promising light-harvesting material for solar cells because of the large absorption coefficient and prominent photoconductivity. However, the efficiency of Se solar cells has been stagnated for a long time owing to the suboptimal bandgap (> 1.8 eV) and the lack of a proper electron transport layer. In this work, we tune the bandgap of the absorber to the optimal value of Shockley-Queisser limit (1.36 eV) by alloying 30% Te with 70% Se. Simultaneously, ZnO electron transport layer is selected because of the proper band alignment, and the mild reaction at ZnO/Se0.7Te0.3 interface guarantees a good-quality heterojunction. Finally, a superior efficiency of 1.85% is achieved on ZnO/Se0.7Te0.3 solar cells.

HTL-Free Sb2(S, Se)3 Solar Cells with an Optimal Detailed Balance Band Gap.

Antimony chalcogenides are widely studied as a light-absorbing material due to their merits of low toxicity, efficient cost, and excellent photovoltaic properties. However, the band gaps of antimony selenide (approximately 1.1 eV) and antimony sulfide (approximately 1.7 eV) both deviate from the optimal detailed balance band gap (∼1.3 eV) for terrestrial single-junction solar cells. Notably, the band gap of Sb2(S, Se)3 can be tunable in the range from 1.1 to 1.7 eV, which can cover the detailed balance band gap. In this work, the vapor transport deposition method with two independent evaporation sources is used to deposit Sb2(S, Se)3 thin films. By carefully optimizing the evaporation temperature and the start evaporation time of the Sb2Se3 and Sb2S3 sources, a suitable band gap of 1.33 eV is obtained. Finally, on the basis of the optimal Sb2(S, Se)3 films, Sb2(S, Se)3 solar cells without a hole transport layer achieved an efficiency of 7.03%.