Recent Issues and Configuration Factors in Perovskite-Silicon Tandem Solar Cells towards Large Scaling Production.

The unprecedented development of perovskite-silicon (PSC-Si) tandem solar cells in the last five years has been hindered by several challenges towards industrialization, which require further research. The combination of the low cost of perovskite and legacy silicon solar cells serve as primary drivers for PSC-Si tandem solar cell improvement. For the perovskite top-cell, the utmost concern reported in the literature is perovskite instability. Hence, proposed physical loss mechanisms for intrinsic and extrinsic instability as triggering mechanisms for hysteresis, ion segregation, and trap states, along with the latest proposed mitigation strategies in terms of stability engineering, are discussed. The silicon bottom cell, being a mature technology, is currently facing bottleneck challenges to achieve power conversion efficiencies (PCE) greater than 26.7%, which requires more understanding in the context of light management and passivation technologies. Finally, for large-scale industrialization of the PSC-Si tandem solar cell, the promising silicon wafer thinning, and large-scale film deposition technologies could cause a shift and align with a more affordable and flexible roll-to-roll PSC-Si technology. Therefore, this review aims to provide deliberate guidance on critical fundamental issues and configuration factors in current PSC-Si tandem technologies towards large-scale industrialization. to meet the 2031 PSC-Si Tandem road maps market target.

An Overview of the Recent Progress in Polymeric Carbon Nitride Based Photocatalysis.

Recently, polymeric carbon nitride (g-C3 N4 ) as a proficient photo-catalyst has been effectively employed in photocatalysis for energy conversion, storage, and pollutants degradation due to its low cost, robustness, and environmentally friendly nature. The critical review summarized the recent development, fundamentals, nanostructures design, advantages, and challenges of g-C3 N4 (CN), as potential future photoactive material. The review also discusses the latest information on the improvement of CN-based heterojunctions including Type-II, Z-scheme, metal/CN Schottky junctions, noble metal@CN, graphene@CN, carbon nanotubes (CNTs)@CN, metal-organic frameworks (MOFs)/CN, layered double hydroxides (LDH)/CN heterojunctions and CN-based heterostructures for H2 production from H2 O, CO2 conversion and pollutants degradation in detail. The optical absorption, electronic behavior, charge separation and transfer, and bandgap alignment of CN-based heterojunctions are discussed elaborately. The correlations between CN-based heterostructures and photocatalytic activities are described excessively. Besides, the prospects of CN-based heterostructures for energy production, storage, and pollutants degradation are discussed.

Rapid fabrication of oxygen defective α-Fe2O3(110) for enhanced photoelectrochemical activities.

Defect engineering is increasingly recognized as a viable strategy for boosting the performance of photoelectrochemical (PEC) water splitting using metal oxide-based photoelectrodes. However, previously developed methods for generating point defects associated with oxygen vacancies are rather time-consuming. Herein, high density oxygen deficient α-Fe2O3 with the dominant (110) crystal plane is developed in a very short timescale of 10 minutes by employing aerosol-assisted chemical vapor deposition and pure nitrogen as a gas carrier. The oxygen-defective film exhibits almost 8 times higher photocurrent density compared to a hematite photoanode with a low concentration of oxygen vacancies which is prepared in purified air. The existence of oxygen vacancies improves light absorption ability, accelerates charge transport in the bulk of films, and promotes charge separation at the electrolyte/semiconductor interface. DFT simulations verify that oxygen-defective hematite has a narrow bandgap, electron-hole trapped centre, and strong adsorption energy of water molecules compared to pristine hematite. This strategy might bring PEC technology another step further towards large-scale fabrication for future commercialization.

Nanostructure-assisted charge transfer in α-Fe2O3/g-C3N4 heterojunctions for efficient and highly stable photoelectrochemical water splitting.

The development of semiconductor heterojunctions is a promising and yet challenging strategy to boost the performance in photoelectrochemical (PEC) water splitting. This paper describes the fabrication of a heterojunction photoanode by coupling α-Fe2O3 and g-C3N4via aerosol-assisted chemical vapour deposition (AACVD) followed by spin coating and air annealing. Enhanced PEC performance and stability are observed for the α-Fe2O3/g-C3N4 heterojunction photoanode in comparison to pristine α-Fe2O3 and the reason is systematically discussed in this paper. Most importantly, the fabricated α-Fe2O3/g-C3N4 film shows impressive stability, retaining more than 90% of the initial current over 12 h operating time. The excellent stability of the heterojunction photoanode is achieved due to the unique nanoflake structure of α-Fe2O3 induced by AACVD. This nanostructure promotes good adhesion with the g-C3N4 particles, as the particles tend to be trapped within the α-Fe2O3 valleys and eventually create strong and large interfacial contacts. This leads to improved separation of charge carriers at the α-Fe2O3/g-C3N4 interface and suppression of charge recombination in the photoanode, which are confirmed by the transient decay time, charge transfer efficiency and electrochemical impedance analysis. Our findings demonstrate the importance of nanostructure engineering for developing heterojunction structures with efficient charge transfer dynamics.

Perovskite Flash Memory with a Single-Layer Nanofloating Gate.

Here we use triple-cation metal-organic halide perovskite single crystals for the transistor channel of a flash memory device. Moreover, we design and demonstrate a 10 nm thick single-layer nanofloating gate. It consists of a ternary blend of two organic semiconductors, a p-type polyfluorene and an n-type fullerene that form a donor:acceptor interpenetrating network that serves as the charge storage unit, and of an insulating polystyrene that acts as the tunneling dielectric. Under such a framework, we realize the first non-volatile flash memory transistor based on a perovskite channel. This simplified, solution-processed perovskite flash memory displays unique performance metrics such as a large memory window of 30 V, an on/off ratio of 9 × 107, short write/erase times of 50 ms, and a satisfactory retention time exceeding 106 s. The realization of the first flash memory transistor using a single-crystal perovskite channel could be a valuable direction for perovskite electronics research.

Effects of Mo vapor concentration on the morphology of vertically standing MoS2 nanoflakes.

Vertically standing MoS2 nanoflakes are favourable in applications such as energy storage devices, hydrogen evolution reactions, and gas sensors due to their large surface area and high density of exposed edges. In this work, we report the effect of Mo vapor concentration on the morphology of vertical MoS2 nanoflakes prepared by chemical vapor deposition at atmospheric pressure. A series of MoS2 samples were grown under different Mo vapor concentrations by varying the separation distance (x) between the MoO3 source and the substrate. Field emission scanning electron microscopy showed the sample grown at x = 1 cm had a high density of vertical flakes (7 vertical flakes µm-2) with an average flake length of ~770 nm and thickness of ~10 nm. As x increased to 4 cm, the average flake length was reduced to ~150 nm while the flake orientation changed from vertical to lateral. That is, high Mo vapor concentration favours the formation of large and vertical MoS2 nanoflakes. However, oversupply of Mo vapor results in significantly thicker flakes. Raman spectra of all samples showed two main peaks at 380 and 407 cm-1 that correspond to the E1 2 g and A1 g vibrational peaks of MoS2. As x decreased from 4 to 1, the peak intensity ratio (E1 2g/A1 g) reduced from 0.58 to 0.42, suggesting greater dominance of vertical flakes at low x. X-ray diffraction data showed a prominent peak at 14.4°, which corresponded to the (002) diffraction peak of 2H MoS2. Transmission electron microscopy verified the flakes consist of eight layers with an interlayer spacing of 0.62 nm. Based on hydrogen evolution reaction measurements, samples with thin flakes have high catalytic activity. This work highlights the importance of optimizing Mo vapor concentration to obtain a high density of thin, large, and vertically standing MoS2 nanoflakes.

A hysteresis-free perovskite transistor with exceptional stability through molecular cross-linking and amine-based surface passivation.

Organo-metal halide perovskite field-effect transistors present serious challenges in terms of device stability and hysteresis in the current-voltage characteristics. Migration of ions located at grain boundaries and surface defects in the perovskite film are the main reasons for instability and hysteresis issues. Here, we introduce a perovskite grain molecular cross-linking approach combined with amine-based surface passivation to address these issues. Molecular cross-linking was achieved through hydrogen bond interactions between perovskite halogens and dangling bonds present at grain boundaries and a hydrophobic cross-linker, namely diethyl-(12-phosphonododecyl)phosphonate, added to the precursor solution. With our approach, we obtained smooth and compact perovskite layers composed of tightly bound grains hence significantly suppressing the generation and migration of ions. Moreover, we achieved efficient surface passivation of the perovskite films upon surface treatment with an amine-bearing polymer, namely polyethylenimine ethoxylated. With our synergistic grain and surface passivation approach, we were able to demonstrate the first perovskite transistor with a complete lack of hysteresis and unprecedented stability upon continuous operation under ambient conditions. Added to the merits are its ambipolar transport of opposite carriers with balanced hole and electron mobilities of 4.02 and 3.35 cm2 V-1 s-1, respectively, its high Ion/Ioff ratio >104 and the lowest sub-threshold swing of 267 mV dec-1 reported to date for any perovskite transistor. These remarkable achievements obtained through a cost-effective molecular cross-linking of grains combined with amine-based surface passivation of the perovskite films open a new era and pave the way for the practical application of perovskite transistors in low-cost electronic circuits.

Stable and null current hysteresis perovskite solar cells based nitrogen doped graphene oxide nanoribbons hole transport layer.

UNLABELLED: Perovskite solar cells are becoming one of the leading technologies to reduce our dependency on traditional power sources. However, the frequently used component poly(3,4-ethylenedioxythiophene) polystyrene sulfonate ( PEDOT: PSS) has several shortcomings, such as an easily corroded indium-tin-oxide (ITO) interface at elevated temperatures and induced electrical inhomogeneity. Herein, we propose solution-processed nitrogen-doped graphene oxide nanoribbons (NGONRs) as a hole transport layer (HTL) in perovskite solar cells, replacing the conducting polymer PEDOT: PSS. The conversion efficiency of NGONR-based perovskite solar cells has outperformed a control device constructed using PEDOT: PSS. Moreover, our proposed NGONR-based devices also demonstrate a negligible current hysteresis along with improved stability. This work provides an effective route for substituting PEDOT: PSS as the effective HTL.

Defect chemistry and defect engineering of TiO2-based semiconductors for solar energy conversion.

This tutorial review considers defect chemistry of TiO2 and its solid solutions as well as defect-related properties associated with solar-to-chemical energy conversion, such as Fermi level, bandgap, charge transport and surface active sites. Defect disorder is discussed in terms of defect reactions and the related charge compensation. Defect equilibria are used in derivation of defect diagrams showing the effect of oxygen activity and temperature on the concentration of both ionic and electronic defects. These defect diagrams may be used for imposition of desired semiconducting properties that are needed to maximize the performance of TiO2-based photoelectrodes for the generation of solar hydrogen fuel using photo electrochemical cells (PECs) and photocatalysts for water purification. The performance of the TiO2-based semiconductors is considered in terms of the key performance-related properties (KPPs) that are defect related. It is shown that defect engineering may be applied for optimization of the KPPs in order to achieve optimum performance.