Lead halide perovskite solar cells have recently emerged as a very promising photovoltaic technology due to their excellent power conversion efficiencies; however, the toxicity of lead and the poor stability of perovskite materials remain two main challenges that need to be addressed. Here, for the first time, we report a lead-free, highly stable CHNHCuBrI compound. The CHNHCuBrI films exhibit extraordinary hydrophobic behavior with a contact angle of ∼90°, and their X-ray diffraction patterns remain unchanged even after 4 h of water immersion. UV/vis absorption spectrum shows that CHNHCuBrI compound has an excellent optical absorption over the entire visible spectrum. We applied this copper-based light absorber in printable mesoscopic solar cell for the initial trial and achieved a power conversion efficiency of ∼0.5%. Our study represents an alternative pathway to develop low-toxic and highly stable organic-inorganic hybrid materials for photovoltaic application.

The Schottky barrier height of Ni on n-GaN has been measured to be 0.56 and 0.66 eV by capacitance–voltage (C–V) and current–density–temperature (J–T) methods, respectively. Gallium nickel (Ga4Ni3) is formed as Ni is deposited on the GaN film, which affects the barrier height markedly. The thermal stability of Ni on GaN is also investigated by annealing these specimens at various temperatures. Specimen annealing at temperatures above 200 °C leads to the formation of nickel nitrides Ni3N and Ni4N at the interface of Ni and GaN. These interfacial compounds change the measured barrier height to 1.0 and 0.8 eV by C–V and J–T methods, respectively. Comparisons of Schottky characteristics of Ni with those of Pt, Pd, Au, and Ti are also discussed.

Results of photoconductivity measurements in undoped n-type and Se-doped GaN epitaxial thin films are presented. Similar to the photoluminescence spectra, the photoconductivity also shows a broad yellow band centered around 2.2 eV. It is found that persistent photoconductivity (PPC) does exist in all the studied thin films. In addition, the PPC effects can be observed for the pumping photon energy down to the yellow band. The results reveal that the origin of the PPC effect and yellow luminescence may arise from the same intrinsic defect. It is shown that the most probable candidate of the intrinsic defect is nitrogen antisite.

Photoluminescence, resonant Raman scattering, and photoconductivity measurements have been employed to study the yellow emission in undoped n-type and a set of Se-doped GaN epitaxial films. It is best described by a transition from the conduction-band edge to a deep acceptor. Unlike the donors and acceptors used in most previous studies that substitute Ga sites, Se atoms can replace N sites. With this unique fact, we identify that the origin of the yellow emission involves the nitrogen antisite. In addition, it is found that persistent photoconductivity can be observed after the yellow band excitation. We further suggest that the nitrogen antisite exhibits a metastable behavior similar to the arsenic antisite in GaAs. ͓S0163-1829͑97͒07735-7͔ YELLOW LUMINESCENCE IN n-TYPE GaN EPITAXIAL FILMS

We demonstrate a superpolishing electrolyte, which consists of acid additives in conventional Cu polishing electrolytes (H 3 PO 4 ), for efficiently planarizing Cu damascene features. The significant additive concentration gradient in features, resulting in a selective Cu dissolution rate within features, is explored as a major mechanism that yields such electrolytes with high planarization efficiency. Moreover, another additive, polyethylene glycol as a suppressor, is also employed to reduce oxygen bubbling on polished films. Consequently, a smooth surface with a complete step height elimination is obtained in a 70 m trench after electropolishing.Chemical mechanical polishing ͑CMP͒ of Cu and barrier metals is widely recognized as the most promising technology for planarizing Cu damascene interconnects. 1-4 However, conventional Cu-CMP slurries contain mechanically hard abrasives that scratch and damage polished Cu surfaces. Recently, Cu electropolishing has been explored as a replacement of Cu-CMP due to its higher polishing rate, lower waste stream, no scratching, and no mechanical stress on substrates. TSMC company announced CMP-free and CMP-less approaches by integrating Cu electropolishing. 5 Sony company announced a 25 m wide line formed by soft polishing technology. 6 They used a complexing agent to block Cu surface and introduced a soft pad to remove Cu complex outside of pattern, thereby producing selective electrochemical dissolution.Cu electroplating generally produces a step on/between damascene features after deposition. Moreover, planarization efficiency ͑PE͒ of Cu electropolishing is a strong function of the feature size ͑also for Cu CMP͒. 7,8 Those issues necessitate additional modifications to conventional polishing techniques. Because Cu dissolution rate depends on the pH value of polishing electrolytes and increases with solution conductivity, an addition of acid additives into polishing electrolytes can enhance Cu removal rate. Based on this mechanism and additive distributions controlled in diffusion limit, a presence of concentration gradient of additives in damascene features forms a selective electrochemical dissolution, thus enhancing step height reduction and improving PE of Cu electropolishing. In this article, we demonstrate a superpolishing electrolyte with high PE by adding acid additives into the polishing electrolyte (H 3 PO 4 ). Additionally, oxygen formation during Cu electropolishing often causes severe etched pits on polished surfaces. With polyethylene glycol ͑PEG͒ as a suppressor in the electrolyte, the overpotential of oxygen formation is significantly elevated, thus leading to less damage on polished surfaces. A polishing electrolyte with those additives can planarize damascene interconnects even with feature sizes in several tens of micrometers. ExperimentalThe patterned wafer used in PE measurements was composed of a 30 nm thick ionized metal plasma ͑IMP͒-TaN layer as the diffusion barrier, a 200 nm thick IMP-Cu film as the seed layer, and a 1.7 m electroplated Cu as the ...

Two different kinds of n-type GaN films were prepared by organometallic vapor phase epitaxy, one by using trimethylgallium (TMGa) and another by using triethylgallium (TEGa) as the alkyl source. Schottky diodes with well-behaved current–voltage and capacitance–voltage characteristics were fabricated. Deep-level transient spectroscopy studies were performed on these samples. Three distinct deep levels, labeled E1, E2, and E3, were measured in the film grown with TMGa, with an activation energy of 0.14, 0.49, and 1.63±0.3 eV, respectively. Only one level, E3, was observed in the film prepared with TEGa.

A TiO2 film photoanode with gradient structure in nanosheet/nanoparticle concentration on the fluorine-doped tin oxide glass from substrate to surface was prepared by a screen printing method. The as-prepared dye-sensitized solar cell (DSSC) based on the gradient film electrode exhibited an enhanced photoelectric conversion efficiency of 6.48%, exceeding that of a pure nanoparticle-based DSSC with the same film thickness by a factor of 2.6. The enhanced photovoltaic performance of the gradient film-based DSSC was attributed to the superior light scattering ability of TiO2 nanosheets within the gradient structure, which was beneficial to light harvesting. Furthermore, the TiO2 nanosheets with exposed {001} facets facilitated the electron transport from dye molecules to the conduction band of TiO2 and further to the conductive glass. Meanwhile, the high specific surface area of TiO2 nanosheets helped the adsorption of dye molecules, and the TiO2 nanoparticle underlayer ensured good electronic contact between the TiO2 film and the fluorine-doped tin oxide glass substrate. The electrochemical impedance spectroscopy measurements further confirmed the electron transport differences between DSSCs based on nanosheet/nanoparticle gradient film electrodes and DSSCs based on nanosheet/nanoparticle homogeneous mixtures, pure TiO2 nanoparticles and pure TiO2 nanosheets with the same film thickness.

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