Structural and Electrical Investigation of Cobalt-Doped NiOx/Perovskite Interface for Efficient Inverted Solar Cells

Inorganic hole-transporting materials (HTMs) for stable and cheap inverted perovskite-based solar cells are highly desired. In this context, NiOx, with low synthesis temperature, has been employed. However, the low conductivity and the large number of defects limit the boost of the efficiency. An approach to improve the conductivity is metal doping. In this work, we have synthesized cobalt-doped NiOx nanoparticles containing 0.75, 1, 1.25, 2.5, and 5 mol% cobalt (Co) ions to be used for the inverted planar perovskite solar cells. The best efficiency of the devices utilizing the low temperature-deposited Co-doped NiOx HTM obtained a champion photoconversion efficiency of 16.42%, with 0.75 mol% of doping. Interestingly, we demonstrated that the improvement is not from an increase of the conductivity of the NiOx film, but due to the improvement of the perovskite layer morphology. We observe that the Co-doping raises the interfacial recombination of the device but more importantly improves the perovskite morphology, enlarging grain size and reducing the density of bulk defects and the bulk recombination. In the case of 0.75 mol% of doping, the beneficial effects do not just compensate for the deleterious one but increase performance further. Therefore, 0.75 mol% Co doping results in a significant improvement in the performance of NiOx-based inverted planar perovskite solar cells, and represents a good compromise to synthesize, and deposit, the inorganic material at low temperature, without losing the performance, due to the strong impact on the structural properties of the perovskite. This work highlights the importance of the interface from two different points of view, electrical and structural, recognizing the role of a low doping Co concentration, as a key to improve the inverted perovskite-based solar cells’ performance

Ligand & band gap engineering: tailoring the protocol synthesis for achieving high-quality CsPbI3 quantum dots

Hot-injection has become the most widespread method used for the synthesis of perovskite quantum dots (QDs) with enormous interest for application in optoelectronic devices. However, there are some aspects of the chemistry involved in this synthesis that have not been completely investigated. In this work, we synthesized ultra-high stable CsPbI3 QDs for more than 15 months by controlling two main parameters: synthesis temperature and the concentration of capping ligands. By increasing the capping ligand concentration during the QD synthesis, we were able to grow CsPbI3 in a broad range of temperatures, improving the photophysical properties of QDs by increasing the synthesis temperature. We achieved the maximum photoluminescence quantum yield (PLQY) of 93% for a synthesis conducted at 185 °C, establishing an efficient surface passivation to decrease the density of non-radiative recombination sites. Under these optimized synthesis conditions, deep red LEDs with an External Quantum Efficiency (EQE) higher than 6% were achieved. The performance of these LEDs is higher than that of the reported CsPbI3 QD-LEDs containing standard capping agents, without additional elements or further element exchange. We show that it is possible to produce stable CsPbI3 QDs with high PLQY and red emission beyond the requirement of the Rec. 2020 standards for red color

Integrated Optical Amplifier–Photodetector on a Wearable Nanocellulose Substrate

Flexible optoelectronics has emerged as an outstanding platform to pave the road toward vanguard technology advancements. As compared to conventional rigid substrates, a flexible technology enables mechanical deformation while maintaining stable performance. The advantages include not only the development to novel applications, but also the implementation of a wearable technology directly in contact with a curved surface. Here the monolithic integration of a perovskite‐based optical waveguide amplifier together with a photodetector on a nanocellulose substrate is shown to demonstrate the feasibility of a stretchable signal manipulation and receptor system fabricated on a biodegradable material. An integrated optical amplifier–photodetector is developed in which the photocurrent is exploited that is generated in the organic–inorganic lead halide perovskite under an applied bias. Such photocurrent does not minimally perturb the amplifier operation and is used to monitor the light signal propagating along the waveguide, opening a broad range of applications for example to regulate the operation temperature

Optimizing Performance and Operational Stability of CsPbI3 Quantum-Dot-Based Light-Emitting Diodes by Interface Engineering

Perovskite light-emitting diodes (PeLEDs) have emerged as a promising candidate for next-generation display technology and lighting applications owing to their high current efficiency, low operating voltage, narrow spectral emission, and tunable emission color. Keys to achieving efficient PeLEDs are, besides an emitter layer with high optical quality, a negligible charge injection barrier between charge injecting layers (CILs) and an optimized thickness of these CILs for a controlled flow of charge carriers through the device. In this study, we systematically optimized hole transport layers and electron transport layers (ETLs) in PeLEDs employing CsPbI3 quantum dots as an emitter layer. We also investigated two bilayer cathodes (Liq/Ag and LiF/Al) with the various ETLs employed in our study and observed that 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) as an ETL improves the band alignment, leading to better electron injection. The improved electron/hole current balance results in ∼63% higher external quantum efficiency (EQE) in PO-T2T-based devices compared to PeLEDs employing other ETLs. In addition, we tracked the operational stability of the different devices observing a correlation with the EQE, where samples with higher EQE (PO-T2T-based devices) also present the highest stable operation at elevated current densities

Development of perovskite optoelectronic devices on flexible substrates

Cotutela amb Amirkabir University of TechnologyCompendi d'articlesIn this thesis, first, the monolithic integration of a perovskite-based optical waveguide amplifier together with a photodetector on a nanocellulose substrate is shown to demonstrate the feasibility of a stretchable signal manipulation and receptor system fabricated on a biodegradable material. An integrated optical amplifier–photodetector is developed in which the photocurrent is exploited that is generated in the organic–inorganic lead halide perovskite under an applied bias. Such photocurrent does not minimally perturb the amplifier operation and is used to monitor the light signal propagating along the waveguide, opening a broad range of applications for example to measure the operation temperature. Then, perovskite quantum dot solar cells (PQDSCs) were systematically investigated with impedance spectroscopy. Despite the evident structural differences with respect to standard perovskite solar cells (PSCs), similar impedance spectra were obtained for PQDSCs, pointing to similar working principles in terms of the active layer. Although there is no consensus about the exact mechanism responsible for low frequency capacitance, the suggested models point to an ion migration origin. Its observation in thin-film and PQDSCs devices implies a similar effect in both. Finally, we synthesized ultra-high stable CsPbI3 QDs by controlling two main parameters: synthesis temperature and the concentration of capping ligands. We achieved the maximum photoluminescence quantum yield (PLQY) of 93% for a synthesis conducted at 185 °C, establishing an efficient surface passivation. Under these optimized synthesis conditions, deep red LEDs with an External Quantum Efficiency (EQE) higher than 6% were achieved. We show that it is possible to produce stable CsPbI3 QDs with high PLQY and red emission beyond the requirement of the Rec. 2020 standards for red color.En esta tesis, en primer lugar, se muestra la integración monolítica de un amplificador de guía de ondas óptico basado en perovskita junto con un fotodetector en un sustrato de nanocelulosa para demostrar la viabilidad de un sistema de manipulación y receptor de señal extensible fabricado en un material biodegradable. Se desarrolla un amplificador- fotodetector óptico integrado en el que se aprovecha la fotocorriente que se genera en la perovskita de haluro de plomo orgánico-inorgánico bajo un potencial aplicado. Dicha fotocorriente no perturba mínimamente el funcionamiento del amplificador y se utiliza para monitorizar la señal de luz que se propaga a lo largo de la guía de ondas, abriendo una amplia gama de aplicaciones, por ejemplo para medir la temperatura de funcionamiento. Luego, las células solares de puntos cuánticos de perovskita (PQDSC) se investigaron sistemáticamente con espectroscopía de impedancia. A pesar de las evidentes diferencias estructurales con respecto a las células solares de perovskita estándar (PSC), se obtuvieron espectros de impedancia similares para las PQDSC, lo que apunta a principios de trabajo similares en términos de la capa activa. Aunque no hay consenso sobre el mecanismo exacto responsable de la capacitancia de baja frecuencia, los modelos sugeridos apuntan a un origen de migración de iones. Su observación en dispositivos de película fina y PQDSCs implica un efecto similar en ambos. Finalmente, sintetizamos QD de CsPbI3 con establilidades ultraaltas controlando dos parámetros principales: la temperatura de síntesis y la concentración de ligandos de protección. Logramos el rendimiento cuántico de fotoluminiscencia máximo (PLQY) del 93% para una síntesis realizada a 185 ° C, estableciendo una pasivación superficial eficiente. En estas condiciones de síntesis optimizadas, se lograron LED de color rojo intenso con una eficiencia cuántica externa (EQE) superior al 6%. Demostramos que es posible producir CsPbI3 QD estables con un PLQY alto y una emisión de rojo más allá del requisito de la Rec. Estándares 2020 para el color rojo.Programa de Doctorat en Cièncie

Blood-borne hepatitis in opiate users in iran: a poor outlook and urgent need to change nationwide screening policy.

OBJECTIVE: Iran has the highest rate of opiate use worldwide. However, most opiate users are not screened for hepatitis virus infections. This study aimed to provide accurate, detailed data on the size of the opiate user population at risk of developing these infections. METHOD: This seroprevalence study was conducted in the city of Shiraz, southern Iran. All participants were screened for HBV, HCV and HIV infection. The data were analyzed with SPSS. RESULT: Among 569 participants, 233 (40.9%) were injection drug users (IDU), 369 (64.8%) were heterosexual, 84 (14.7%) were bisexual and 15 (2.6%) were homosexual. One hundred nine (19.1%) were HCV antibody-positive, 18 (3.1%) were HBS antigen-positive, 72 (12.6%) were HBc antibody-positive and 23 (4%) were HIV-positive. Among IDU compared to non-IDU, positivity rates for HBS antigen (5.5 vs 1.4%), HBc antibody (22.7 vs 5.6%), HCV antibody (40.3 vs 4.4%) and HIV (7.7 vs 1.4%) were higher (P < 0.05). Most patients with HBV (80.7%) and HCV infection (83.4%) were HIV-negative. In the cumulative analysis, only history of imprisonment was a statistically significant determinant of infection by HCV or HBV in opiate users. CONCLUSION: The current policy of screening only HIV-positive drug users for HBV and HCV in Iran misses most cases of HBV and HCV infection. We therefore recommend urgent revision of the nationwide protocol by the Ministry of Health in Iran to implement routine screening of all opiate users and especially IDU for these viruses, regardless of their HIV status

Operation Mechanism of Perovskite Quantum Dot Solar Cells Probed by Impedance Spectroscopy

We fabricated perovskite quantum dot solar cells (PQDSCs) and varied the thickness of the QD layer by controlling the number of deposition cycles; the cells were systematically investigated with impedance spectroscopy. Despite the evident structural differences with respect to standard perovskite solar cells (PSCs), similar impedance spectra were obtained for PQDSCs, pointing to similar working principles in terms of the active layer. We distinguish two different regimes: At low illumination, recombination is ruled by multiple trapping with trap distributions and/or shunting. However, at higher light intensities, Shockley–Read–Hall recombination is observed. In addition, the low-frequency capacitance, CLF, of PQDSCs increases several orders of magnitude when the illumination is varied from dark to 1-sun conditions. This feature has not been observed in other kinds of photovoltaic devices and is characteristic of PSCs. Although there is no consensus about the exact mechanism responsible for CLF, the suggested models point to an ion migration origin. Its observation in thin-film and PQDSCs devices implies a similar effect in both

Optical Optimization of the TiO2 Mesoporous Layer in Perovskite Solar Cells by the Addition of SiO2 Nanoparticles

In this work, SiO2 nanoparticles (NPs) were integrated into the mesoporous TiO2 layer of a perovskite solar cell to investigate their effect on cell performance. Different concentrations of SiO2/ethanol have been combined in TiO2/ethanol to prepare pastes for the fabrication of the mesoporous layer with which perovskite solar cells have been fabricated. Addition of SiO2 NPs of 50 and 100 nm sizes produces an enhancement of cell performance mainly because of an improvement of the photocurrent. This increment is in good agreement with the theoretical predictions based on light scattering induced by dielectric SiO2 NPs. The samples using modified scaffolds with NPs also present a significant lower current–potential hysteresis indicating that NP incorporation also affects the ion accumulation at the perovskite interface, providing an additional beneficial effect. The results stress the importance of the appropriated management of the optical properties on further optimization of perovskite solar cell technology

Demographic characteristics and risky behaviors in participants referred to the behavioral counseling center affiliated with Shiraz University of Medical Sciences, southern Iran.

†<p><b>IDU: Intravenous drug Users</b></p