Light capture and pigment diversity in marine and freshwater cryptophytes

Phenotypic traits associated with light capture and phylogenetic relationships were characterized in 34 strains of diversely pigmented marine and freshwater cryptophytes. Nuclear SSU and partial LSU rDNA sequence data from 33 of these strains plus an additional 66 strains produced a concatenated rooted maximum likelihood tree that classified the strains into 7 distinct clades. Molecular and phenotypic data together support: (i) the reclassification of Cryptomonas irregularis NIES 698 to the genus Rhodomonas, (ii) revision of phycobiliprotein (PBP) diversity within the genus Hemiselmis to include cryptophyte phycocyanin (Cr‐PC) 569, (iii) the inclusion of previously unidentified strain CCMP 2293 into the genus Falcomonas, even though it contains cryptophyte phycoerythrin 545 (Cr‐PE 545), and (iv) the inclusion of previously unidentified strain CCMP 3175, which contains Cr‐PE 545, in a clade with PC‐containing Chroomonas species. A discriminant analysis‐based model of group membership correctly predicted 70.6% of the clades using three traits: PBP concentration · cell^?1, the wavelength of PBP maximal absorption, and habitat. Non‐PBP pigments (alloxanthin, chl‐a, chl‐c₂, α‐carotene) did not contribute significantly to group classification, indicating the potential plasticity of these pigments and the evolutionary conservation of the PBPs. Pigment data showed evidence of trade‐offs in investments in PBPs vs. chlorophylls (a +c₂).     

Hybrid Heterojunction and Solid‐State Photoelectrochemical Solar Cells

A hybrid heterojunction and solid‐state photoelectrochemical solar cell based on graphene woven fabrics (GWFs) and silicon is designed and fabricated. The GWFs are transferred onto n‐Si to form a Schottky junction with an embedded polyvinyl alcohol based solid electrolyte. In the hybrid solar cell, solid electrolyte serves three purposes simutaneously; it is an anti‐reflection layer, a chemical modification carrier, and a photoelectrochemical channel. The open‐circuit voltage, short‐circuit current density, and fill factor are all significantly improved, achieving an impressive power conversion efficiency of 11%. Solar cell models are constructed to confirm the hybrid working mechanism, with the heterojunction junction and photoelectrochemical effect functioning synergistically.     

Metal‐Oxide‐Free Methylammonium Lead Iodide Perovskite‐Based Solar Cells: the Influence of Organic Charge Transport Layers

Metal‐oxide‐free methylammonium lead iodide perovskite‐based solar cells are prepared using a dual‐source thermal evaporation method. This method leads to high quality reproducible films with large crystal domain sizes allowing for an in depth study of the effect of perovskite film thickness and the nature of the electron and hole blocking layers on the device performance. The power conversion efficiency increases from 4.7% for a device with only an organic electron blocking layer to almost 15% when an organic hole blocking layer is also employed. In addition to the in depth study on small area cells, larger area cells (approx. 1 cm^?2) are prepared and exhibit efficiencies in excess of 10%.     

Development of Dopant‐Free Organic Hole Transporting Materials for Perovskite Solar Cells

There has been considerable progress over the last decade in development of the perovskite solar cells (PSCs), with reported performances now surpassing 25.2% power conversion efficiency. Both long‐term stability and component costs of PSCs remain to be addressed by the research community, using hole transporting materials (HTMs) such as 2,2′,7,7′‐tetrakis(N,N′‐di‐pmethoxyphenylamino)‐9,9′‐spirbiuorene(Spiro‐OMeTAD) and poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA). HTMs are essential for high‐performance PSC devices. Although effective, these materials require a relatively high degree of doping with additives to improve charge mobility and interlayer/substrate compatibility, introducing doping‐induced stability issues with these HTMs, and further, additional costs and experimental complexity associated with using these doped materials. This article reviews dopant‐free organic HTMs for PSCs, outlining reports of structures with promising properties toward achieving low‐cost, effective, and scalable materials for devices with long‐term stability. It summarizes recent literature reports on non‐doped, alternative, and more stable HTMs used in PSCs as essential components for high‐efficiency cells, categorizing HTMs as reported for different PSC architectures in addition to use of dopant‐free small molecular and polymeric HTMs. Finally, an outlook and critical assessment of dopant‐free organic HTMs toward commercial application and insight into the development of stable PSC devices is provided.     

Elucidating the Role of a Tetrafluoroborate‐Based Ionic Liquid at the n‐Type Oxide/Perovskite Interface

Halide perovskites are currently one of the most heavily researched emerging photovoltaic materials. Despite achieving remarkable power conversion efficiencies, perovskite solar cells have not yet achieved their full potential, with the interfaces between the perovskite and the charge‐selective layers being where most recombination losses occur. In this study, a fluorinated ionic liquid (IL) is employed to modify the perovskite/SnO₂ interface. Using Kelvin probe and photoelectron spectroscopy measurements, it is shown that depositing the perovskite onto an IL‐treated substrate results in the crystallization of a perovskite film which has a more n‐type character, evidenced by a decrease of the work function and a shift of the Fermi level toward the conduction band. Photoluminescence spectroscopy and time‐resolved microwave conductivity are used to investigate the optoelectronic properties of the perovskite grown on neat and IL‐modified surfaces and it is found that the modified substrate yields a perovskite film which exhibits an order of magnitude lower trap density than the control. When incorporated into solar cells, this interface modification results in a reduction in the current–voltage hysteresis and an improvement in device performance, with the best performing devices achieving steady‐state PCEs exceeding 20%.     

Highly Air‐Stable Single‐Crystalline β‐CsPbI3 Nanorods: A Platform for Inverted Perovskite Solar Cells

The synthesis of single‐crystalline β‐CsPbI₃ perovskite nanorods (NRs) using a colloidal process is reported, exhibiting their improved photostability under 45–55% humidity. The crystal structure of CsPbI₃ NRs films is investigated using Rietveld refined X‐ray diffraction (XRD) patterns to determine crystallographic parameters and the phase transformation from orthorhombic (γ‐CsPbI₃) to tetragonal (β‐CsPbI₃) on annealing at 150 °C. Atomic resolution transmission electron microscopy images are utilized to determine the probable atomic distribution of Cs, Pb, and I atoms in a single β‐phase CsPbI₃ NR, in agreement with the XRD structure and selected area electron diffraction pattern, indicating the growth of single crystalline β‐CsPbI₃ NR. The calculation of the electronic band structure of tetragonal β‐CsPbI₃ using density functional theory (DFT) reveals a direct transition with a lower band gap and a higher absorption coefficient in the solar spectrum, as compared to its γ‐phase. An air‐stable (45–55% humidity) inverted perovskite solar cell, employing β‐CsPbI₃ NRs without any encapsulation, yields an efficiency of 7.3% with 78% enhancement over the γ‐phase, showing its potential for future low cost photovoltaic devices.     

PHOTOSYNTHETIC RESPONSE OF NATURAL ASSEMBLAGES OF MARINE BENTHIC MICROALGAE TO SHORT-AND LONG-TERM VARIATIONS OF INCIDENT IRRADIANCE IN BAFFIN BAY,TEXAS1

This study was designed to understand the high variability characterizing primary production rates of microphytobenthos. The photosynthetic efficiency (α^B) and photosynthetic capacity (P^B_max) of the microphytobenthos were measured at different times of the day on two different dates (8 May and 7 July 1990). In July, unusually low light conditions were caused by the development of a brown tide (chrysophytes). Both light-limited and light-saturated photosynthesis changed at hourly and monthly scales. There was a linear relationship between α^B and P^B_max, suggesting a common response to environmental factors [α^B= 0.0075(±0.00063)·P^B_max+ 0.00097(±0.0071), R²= 0.94]. Incident irradiance at the sediment-water interface was the primary physical factor that explained variability of both α^B (84%) and P^B_max (92%). Temperature had a negative but minor effect that explained an extra 8% and 2% of the variance, respectively. There was no diel rhythm of α^B and P^B_max and incident irradiance was regulated by wind-induced currents. Therefore, microphytobenthos photosynthesis seemed to be primarily controlled by wind events in Baffin Bay.     

Carbon: terrestrial C4 plants

The carbon isotope composition of terrestrial C₄ plants depends on the primary carboxylation of phosphoenolpyruvate (PEP) and on the diffusion of CO₂ to the carboxylation sites, but is also influenced by the final carboxylation of ribulose-1,5-bisphosphate (RuBP). Several models have been used for reproducing this complex situation. In the present review, a particular model is applied as a means to interpret the effects of environmental and genetically determined factors on carbon isotope discrimination during C₄ photosynthesis. As a new feature, the model considers four types of limitation of the overall CO₂ assimilation rate. Both carboxylation reactions are assumed to be limited by either maximum enzyme activity or maximum substrate regeneration rate. The model is applied to experimental data on the effects of CO₂, irradiance and water stress on short-term discrimination by leaves of several C₄ species measured simultaneously with CO₂ gas exchange characteristics. In particular, different patterns of the influence of low irradiances on carbon isotope discrimination are interpreted as due to variations in that irradiance at which a transition from limitation by PEP regeneration rate and RuBP carboxylase activity to limitation by the regeneration rates of both substrates occurs. After discussing literature data on the effects of environmental conditions on carbon isotope discrimination by C₄ plants seasonal and developmental changes in carbon isotope composition, studies on the systematic and geographic distribution of C₄ plants, evolutionary and genetical aspects, and some ecological implications are reviewed.