Possible atomic structures for the sub-bandgap absorption of chalcogen hyperdoped silicon

Single-crystal silicon wafers were hyperdoped respectively by sulfur, selenium, and tellurium element using ion implantation and nanosecond laser melting. The hyperdoping of such chalcogen elements endowed the treated silicon with a strong and wide sub-bandgap light absorptance. When these hyperdoped silicons were thermally annealed even at low temperatures (such as 200~400 oC), however, this extra sub-bandgap absorptance began to attenuate. In order to explain this attenuation of absorptance, alternatively, we consider it corresponding to a chemical decomposition reaction from optically absorbing structure to non-absorbing structure, and obtain a very good fitting to the attenuated absorptances by using Arrhenius equation. Further, we extract the reaction activation energies from the fittings and they are 0.343(+/- 0.031) eV for S-, 0.426(+/-0.042) eV for Se-, and 0.317(+/-0.033) eV for Te-hyperdoped silicon, respectively. We discuss these activation energies in term of the bond energies of chalcogen-Si metastable bonds, and finally suggest that several high-energy interstitial sites instead of the substitutional site, are very possibly the atomic structures that are responsible for the sub-bandgap absorptance of chalcogen hyperdoped silicon.Comment: 18 pages, 3 figures, 1 tabl

Preparation of SnS2 colloidal quantum dots and their application in organic/inorganic hybrid solar cells

Dispersive SnS2 colloidal quantum dots have been synthesized via hot-injection method. Hybrid photovoltaic devices based on blends of a conjugated polymer poly[2-methoxy-5-(3",7"dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as electron donor and crystalline SnS2 quantum dots as electron acceptor have been studied. Photoluminescence measurement has been performed to study the surfactant effect on the excitons splitting process. The photocurrent of solar cells with the hybrid depends greatly on the ligands exchange as well as the device heat treatment. AFM characterization has demonstrated morphology changes happening upon surfactant replacement and annealing, which can explain the performance variation of hybrid solar cells

Efficient organic solar cells enabled by simple non-fused electron donors with low synthetic complexity

Abstract Fused‐ring electron donors boost the efficiency of organic solar cells (OSCs), but they suffer from high cost and low yield for their large synthetic complexity (SC > 30%). Herein, the authors develop a series of simple non‐fused‐ring electron donors, PF1 and PF2, which alternately consist of furan‐3‐carboxylate and 2,2′‐bithiophene. Note that PF1 and PF2 present very small SC of 9.7% for their inexpensive raw materials, facile synthesis, and high synthetic yield. Compared to their all‐thiophene‐backbone counterpart PT‐E, two new polymers feature larger conjugated plane, resulting in higher hole mobility for them, especially a value up to ≈10 −4 cm 2 V −1 ·s for PF2 with longer alkyl side chain. Meanwhile, PF1 and PF2 exhibit larger dielectric constant and deeper electronic energy level versus PT‐E. Benefiting from the better physicochemical properties, the efficiencies of PF1‐ and PF2‐based devices are improved by ≈16.7% and ≈71.3% relative to that PT‐E‐based devices, respectively. Furthermore, the optimized PF2‐based devices with introducing PC 71 BM as the third component deliver a higher efficiency of 12.40%. The work not only indicates that furan‐3‐carboxylate is a simple yet efficient building block for constructing non‐fused‐ring polymers but also provides a promising electron donor PF2 for the low‐cost production of OSCs.A simple structure non‐fused‐ring electron donor PF2 alternately consisting of furan‐3‐carboxylate and 2,2′‐bithiophene presents very small synthetic complexity of 9.7% as well as low material cost of ≈19.0 $ g −1 . More importantly, PF2 delivers a high efficiency of 12.4% coupled with strong operational stability. imag

Fully understanding the positive roles of plasmonic nanoparticles in ameliorating the efficiency of organic solar cells

Herein, we constructed inverted PBDTTT-CF:PC70BM bulk-heterojunction organic solar cells by introducing Au nanoparticles to a ZnO buffer layer and a great improvement in energy conversion efficiency has been realized. To discover the positive roles of such plasmonic nanoparticles in the process of solar energy conversion, photovoltaic devices with the same architecture but different sized Au nanoparticles were purposely fabricated and it has been observed that the overall efficiency can be remarkably improved from 6.67% to 7.86% by embedding 41 nm Au nanoparticles in the buffer layer. The devices with other sizes of Au nanoparticles show a relatively low performance. Subsequent investigations including finite difference time domain simulation and transient photoluminescence studies reveal that the existence of the plasmonic particles could not only improve the optical absorption and facilitate the exciton separation, but can also benefit the collection of charge carriers. Thus, this paper provides a comprehensive perspective on the roles of plasmonic particles in organic solar cells and insights into the photo energy conversion process in the plasmonic surroundings

Analysis of Surface Sound Duct in the Northern Shelf of the South China Sea

The northern shelf of the South China Sea (NSSCS) is characterized by surface low-salinity water due to discharge from the Pearl River. In such an environment, the surface sound duct (SSD) is the most important duct for near-surface sonar applications. Nevertheless, the mechanism of SSD formation is very complicated and is influenced by salinity, temperature at the air-sea interface, and various additional marine phenomena. In this study, an 8-year conductivity-temperature-depth (CTD) profile of the NSSCS was used to analyze the SSD formation. An advanced diagrammatic method is proposed to provide a quantitative analysis of the contribution of salinity, temperature, and hydrostatic pressure on SSD formation. Large salinity gradient (0.25 psu/m) was shown to play a crucial role in SSD formation when a mixed layer exists. As representative examples, the sea under cold surges, typhoon genesis, and low-salinity lenses were studied. Conversely, the absence of SSDs in low-salinity water was also observed in upwelling regions. This study further showed that highly negative temperature gradients affect SSD formation even in low-salinity water. Furthermore, although the duct depth of a low-salinity SSD is usually less than 10 meters, it still can serve as an effective duct for acoustic propagation

Hybrid morphology dependence of CdTe:CdSe bulk-heterojunction solar cells

A nanocrystal thin-film solar cell operating on an exciton splitting pattern requires a highly efficient separation of electron-hole pairs and transportation of separated charges. A hybrid bulk-heterojunction (HBH) nanostructure providing a large contact area and interpenetrated charge channels is favorable to an inorganic nanocrystal solar cell with high performance. For this freshly appeared structure, here in this work, we have firstly explored the influence of hybrid morphology on the photovoltaic performance of CdTe:CdSe bulk-heterojunction solar cells with variation in CdSe nanoparticle morphology. Quantum dot (QD) or nanotetrapod (NT)-shaped CdSe nanocrystals have been employed together with CdTe NTs to construct different hybrid structures. The solar cells with the two different hybrid active layers show obvious difference in photovoltaic performance. The hybrid structure with densely packed and continuously interpenetrated two phases generates superior morphological and electrical properties for more efficient inorganic bulk-heterojunction solar cells, which could be readily realized in the NTs:QDs hybrid. This proved strategy is applicable and promising in designing other highly efficient inorganic hybrid solar cells