• Energy Research

The race to the future generation of low‐cost photovoltaic devices continuously takes on added momentum with the appearance of novel practical solutions for the fabrication of perovskite solar cells (PSCs), a paradigm technology for ultracheap light‐to‐electricity conversion. Much has been done in the past few years toward defining standard protocols for the assessment of their efficiency and stability, aiming at achieving a worldwide consensus on the issue, that will allow reliable reporting of new data. While this is undoubtedly a step ahead toward commercialization of these devices, it also often triggers researchers to test record architectures using benchmark configurations, mainly for what regards the ancillary layers that extract electrical charges from the photoexcited perovskite. In particular, the mostly used hole‐transporting material (HTM) is the small‐molecule spiro‐OMeTAD, which is also well known to be the origin of PSC degradation after prolonged operation. Herein, it is aimed to remark the huge impact of the HTM on PSC performance, recalling major issues associated with the conventional spiro‐based one and providing an overview of state‐of‐the‐art alternatives. Finally, possible scenarios for the future development of smart HTMs are also envisioned, as charge‐extracting layers, with a real active role in ensuring PSC operational stability.

The interest in layered 2D nanomaterials has witnessed an impressive growth in the last years, bringing to the discovery of many new species and methods for their preparation. The liquid-phase exfoliation (LPE) of crystalline bulk powders is certainly the most suitable method for scaled-up production, allowing also the convenient access to solution processing techniques for the direct utilization of the produced 2D material colloidal inks. Given the large number of reports on LPE processes for different 2D materials, today, it is necessary to specifically define the results of similar investigations, so as to provide the scientific community with clear guidelines for identifying design rules and applying standardized procedures. In this work, we present a systematic study on the LPE process for α-MoO3, a stable high band gap semiconductor, which in its 2D form has been employed for many purposes, ranging from catalysis to energy/optoelectronic devices and sensing. We investigate the effect of different low-toxicity solvents and instruments for its LPE and provide new insights into the structural and electronic properties of the resulting 2D nano-inks in a joint experimental–computational effort, which will represent a solid source of information for the future implementation of liquid-dispersed layered α-MoO3 nanosheets in different fields.

While direct optical excitation of carbon nanotubes activates only the tube species strictly matching the excitation source, excitation energy transfer processes provide a single excitation channel for all the nanotubes species in a sample. The requirement of an overlap between donor emission and acceptor absorption limits the poll of donors able to trasfer their excitation to the tubes, leaving the high‐energy part of the solar spectrum excluded from such processes. Here it is shown that the grafting of small metal nanoparticles to the tubes alters those rules, enabling energy transfer process from molecules for which the standard energy transfer process is strongly suppressed. The onset of an energy transfer band in the UV/blue spectral region is demonstrated for an hybrid gold‐pyrene‐nanotube system, yielding collective emission from all the tubes present in our samples upon excitation of pyrene.

Abstract Silver-bismuth double perovskites are promising replacement materials for lead-based ones in photovoltaic (PV) devices due to the lower toxicity and enhanced stability to environmental factors. In addition, they might even be more suitable for indoor PV, due to the size of their bandgap better matching white LEDs emission. Unfortunately, their optoelectronic performance does not reach that of the lead-based counterparts, because of the indirect nature of the band gap and the high exciton binding energy. One strategy to improve the electronic properties is the dimensional reduction from the 3D to the 2D perovskite structure, which features a direct band gap, as it has been reported for 2D monolayer derivates of Cs2AgBiBr6 obtained by substituting Cs+ cations with bulky alkylammonium cations. However, a similar dimensional reduction also brings to a band gap opening, limiting light absorption in the visible. In this work, we report on the achievement of a bathochromic shift in the absorption features of a butylammonium-based silver-bismuth bromide monolayer double perovskite through doping with iodide and study the optical properties and stability of the resulting thin films in environmental conditions. These species might constitute the starting point to design future sustainable materials to implement as active components in indoor photovoltaic devices used to power the IoT.

Two-dimensional (2D) layered nanomaterial heterostructures, arising from the combination of 2D materials with other low-dimensional species, feature a large surface area to volume ratio, which provides a high density of active sites for catalytic applications and for (photo)electrocatalysis (PEC). Meanwhile, their electronic band structure and high electrical conductivity enable efficient charge transfer (CT) between the active material and the substrate, which is essential for catalytic activity. In recent years, researchers have demonstrated the potential of a range of 2D material interfaces, such as graphene, graphitic carbon nitride (g-C3N4), metal chalcogenides (MCs), and MXenes, for (photo)electrocatalytic applications. For instance, MCs such as MoS2 and WS2 have shown excellent catalytic activity for hydrogen evolution, while graphene and MXenes have been used for the reduction of carbon dioxide to higher value chemicals. However, despite their great potential, there are still major challenges that need to be addressed to fully realize the potential of 2D materials for PEC. For example, their stability under harsh reaction conditions, as well as their scalability for large-scale production are important factors to be considered. Generating heterojunctions (HJs) by combining 2D layered structures with other nanomaterials is a promising method to improve the photoelectrocatalytic properties of the former. In this review, we inspect thoroughly the recent literature, to demonstrate the significant potential that arises from utilizing 2D layered heterostructures in PEC processes across a broad spectrum of applications, from energy conversion and storage to environmental remediation. With the ongoing research and development, it is likely that the potential of these materials will be fully expressed in the near future.

AbstractThe need to develop sustainable energy solutions is an urgent requirement for society, with the additional requirement to limit dependence on critical raw materials, within a virtuous circular economy model. In this framework, it is essential to identify new avenues for light‐conversion into clean energy and fuels exploiting largely available materials and green production methods. Metal oxide semiconductors (MOSs) emerge among other species for their remarkable environmental stability, chemical tunability, and optoelectronic properties. MOSs are often key constituents in next generation energy devices, mainly in the role of charge selective layers. Their use as light harvesters is hitherto rather limited, but progressively emerging. One of the key strategies to boost their properties involves doping, that can improve charge mobility, light absorption and tune band structures to maximize charge separation at heterojunctions. In this review, effective methods to dope MOSs and to exploit the derived benefits in relation to performance enhancement in different types of devices are identified and critically compared. The work is focused specifically on the best opportunities coming from the use of non‐critical raw materials, so as to contribute in defining an economically feasible roadmap for light conversion technologies based on these highly stable and widely available compounds.