Ab initio Study of Anchoring Groups for CuGaO2 Delafossite-Based p-Type Dye Sensitized Solar Cells

Improved Power Conversion Efficiency with Tunable Electronic Structures of the Cation-Engineered [Ai]PbI3 Perovskites for Solar Cells: First-Principles Calculations

Higher power conversion efficiencies for photovoltaic devices can be achieved through simple and low production cost processing of APbI3(A=CH3NH3,CHN2H4,…) perovskites. Due to their limited long-term stability, however, there is an urgent need to find alternative structural combinations for this family of materials. In this study, we propose to investigate the prospects of cation-substitution within the A-site of the APbI3 perovskite by selecting nine substituting organic and inorganic cations to enhance the stability of the material. The tolerance and the octahedral factors are calculated and reported as two of the most critical geometrical features, in order to assess which perovskite compounds can be experimentally designed. Our results showed an improvement in the thermal stability of the organic cation substitutions in contrast to the inorganic cations, with an increase in the power conversion efficiency of the Hydroxyl-ammonium (NH3OH) substitute to η = 25.84%.

First-Principles Study of Cu-Based Inorganic Hole Transport Materials for Solar Cell Applications

Perovskite solar cells (PSCs) and dye-sensitized solar cells (DSCs) both represent promising strategies for the sustainable conversion of sunlight into electricity and fuels. However, a few flaws of current devices hinder the large-scale establishment of such technologies. On one hand, PSCs suffer from instabilities and undesired phenomena mostly linked to the perovskite/hole transport layer (HTL) interface. Most of the currently employed organic HTL (e.g., Spiro-OMeTAD) are supposed to contribute to the perovskite decomposition and to be responsible for charge recombination processes and polarization barriers. On the other hand, power conversion efficiencies (PCEs) of DSCs are still too low to compete with other conversion technologies. Tandem cells are built by assembling p-type and n-type DSCs in a cascade architecture and, since each dye absorbs on a different portion of the solar spectrum, the harvesting window is increased and the theoretical efficiency limit for a single chromophore (i.e., the Shockley-Queisser limit) is overcome. However, such a strategy is hindered by the lack of a p-type semiconductor with optimal photocathode features. Nickel oxide has been, by far, the first-choice inorganic p-type semiconductor for both PV technologies, but its toxicity and non-optimal features (e.g., too low open circuit voltage and the presence of trap states) call for alternatives. Herein, we study of three p-type semiconductors as possible alternative to NiO, namely CuI, CuSCN and Cu₂O. To this aim, we compare the structural and electronic features of the three materials by means of a unified theoretical approach based on the state-of-the art density functional theory (DFT). We focus on the calculation of their valence band edge energies and compare such values with those of two widely employed photo-absorbers, i.e., methylammonium lead iodide (MAPI) and the triple cation MAFACsPbBrI in PSCs and P1 and Y123 dyes in DSCs, given that the band alignment and the energy offset are crucial for the charge transport at the interfaces and have direct implications on the final efficiency. We dissect the effect a copper vacancy (i.e., intrinsic p-type doping) on the alignment pattern and rationalize it from both a structural and an electronic perspective. Our data show how defects can represent a crucial degree of freedom to control the driving force for hole injection in these devices.

Hydrothermal synthesized delafossite CuGaO2 as an electrocatalyst for water oxidation

Hydrogen production from water splitting provides an effective method to alleviate the ever-growing global energy crisis. In this work, delafossite CuGaO₂ (CGO) crystal was synthesized through hydrothermal routes with Cu(NO₃)₂·3H₂O and Ga(NO₃)₃·xH₂O used as reactants. The addition of cetyltrimethylammonium bromide (CTAB) was found to play an important role in modifying the morphology of CuGaO₂ (CGO-CTAB). With the addition of CTAB, the morphology of CGO-CTAB samples changed from irregular flake to typical hexagonal sheet microstructure, with an average size of 1-2 μm and a thickness of around 100 nm. Furthermore, the electrocatalytic activity of CGO-CTAB crystals for oxygen evolution reaction (OER) was also studied and compared with that of CGO crystals. CGO-CTAB samples exhibited better activity than CGO. An overpotential of 391.5 mV was shown to be able to generate a current density of 10 mA/cm². The as-prepared samples also demonstrate good stability for water oxidation and relatively fast OER kinetics with a Tafel slope of 56.4 mV/dec. This work highlights the significant role of modification of CTAB surfactants in preparing CGO related crystals, and the introduction of CTAB was found to help to improve their electrocatalytic activity for OER.

Dye-sensitized solar cells strike back

Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. In recent years, DSCs and dye-sensitized photoelectrochemical cells (DSPECs) have experienced a renaissance as the best technology for several niche applications that take advantage of DSCs' unique combination of properties: at low cost, they are composed of non-toxic materials, are colorful, transparent, and very efficient in low light conditions. This review summarizes the advancements in the field over the last decade, encompassing all aspects of the DSC technology: theoretical studies, characterization techniques, materials, applications as solar cells and as drivers for the synthesis of solar fuels, and commercialization efforts from various companies.

P-type transparent conducting characteristics of delafossite Ca doped CuScO2 prepared by hydrothermal synthesis

Ca doped CuScO2 (CSO) delafossite oxides of 3-4 μm were synthesized through the hydrothermal method using Cu(NO3)2·3H2O, Sc(NO3)3·xH2O as the precursor at 240 °C for 24 h in this work. The influence of the process parameters (reaction temperature, Cu/Sc molar ratios, EG (ethylene glycol) quantity, NaOH mineralizer, reactant concentration) on the structure and morphology of CSO was studied systematically. The crystal structure, morphology, and chemical composition of these Ca doped CSO (0, 1 at%, 3 at%, and 5 at%) sheets were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). With increasing Ca dopant, the Ca doped CSO sheets become much thinner; the thickness decreased from 568 nm (CSO) to 190 nm (3 at% Ca doped CSO). Moreover, the conductivity of Ca doped CSO sheets decreased with increasing Ca dopant. The CSO powders (19.91 S m-1) have higher conductivity than Ca doped CSO sheets (9.89, 15.69, and 16.51 S m-1) at room temperature. All these CSO based samples exhibit a weak absorption ability with the absorptance around 20-40% in the visible light region (400-780 nm). The optical band gap values exhibited a blue shift with increasing Ca dopant. The calculated band gaps of Ca-doped CSO sheets are 3.88 eV, 3.91 eV, 3.90 eV and 3.93 eV, respectively. This result indicates that all these CSO based samples have potential applications as p-type transparent materials in optoelectronic devices, owing to their comparable optical transmittance in the UV-vis region.

Theoretical Study of Effects of Anchoring Groups on Photovoltaic Properties of a Triarylamine-Based p-Type Sensitizer

The effects of anchoring groups on triarylamine-based p-type dyes were studied by substituting the strong electron-withdrawing carboxyl group with the weak electron-withdrawing pyridyl and the electron-rich catechol groups. Judged by the index t, the charge separation would be improved greatly when the carboxyl group of P4 is replaced by the pyridyl or catechol groups. Although carboxyl as an anchoring group lowers the HOMO energy and facilitates the hole injection in comparison with pyridyl and catechol groups, the weak electron-withdrawing pyridyl and the electron-rich catechol groups facilitate the charge separation. E _g becomes narrow as the electron-withdrawing abilities of the anchoring groups decrease or as the conjugation extends. Both the extended π-spacers and the substitution of carboxyl with pyridyl and catechol groups promote the redshifts of adsorption wavelengths. The oscillator strengths for all dyes are over 2.00, indicating that all the dyes are able to harvest the sunlight strongly. The ΔG _CR values of P4, DF4, and DZ4 are smaller than those of the other dyes. Also, these dyes have larger adsorption over infrared visible light, indicating that these dyes may be good candidates for p-type DSSCs.

Hierarchical NiO/CMK-3 Photocathode for a p-Type Dye-Sensitized Solar Cell with Improved Photoelectrochemical Performance and Fast Hole Transfer

The sluggish photoelectrochemical performance of p-type dye-sensitized solar cells (p-DSSCs) has hindered its commercial use. In this work, we introduce a novel hierarchical nanocomposite of NiO nanoparticles anchored on highly ordered mesoporous carbons CMK-3 (NiO/CMK-3). Using CMK-3 as a backbone effectively prevented the self-aggregation of NiO nanoparticles and subsequently increased the total specific surface area of the composite for more dye adsorption. The interconnected conductive networks of CMK-3 also served as a split-flow high-speed channel, which was beneficial for hole spin-flow to accelerate hole transfer. The hierarchical NiO/CMK-3 photocathode improved the photovoltaic conversion efficiency to 1.48% in a cell with a Cobalt(II)/(III) electrolyte and a PMI-6T-TPA dye.

Interfacial electronic features in methyl-ammonium lead iodide and p-type oxide heterostructures: new insights for inverted perovskite solar cells

First-principles simulations unveil the interface electronic structures of MAPI/NiO and MAPI/CuGaO₂ heterojunctions in inverted perovskite solar cells.