Evolution of Electronic Structures of Polar Phthalocyanine-Substrate Interfaces

Structural Decoration of Porphyrin/Phthalocyanine Photovoltaic Materials

Porphyrin/phthalocyanine compounds with fascinating molecular structures have attracted widespread attention in the field of solar cells in recent years. In this review, we focus on the pivotal role of porphyrin and phthalocyanine compounds in enhancing the efficiency of solar cells. The review seamlessly integrates the intricate molecular structures of porphyrins and phthalocyanines with their proficiency in absorbing visible light and facilitating electron transfer, key processes in converting sunlight into electricity. By delving into the nuances of intramolecular regulation, aggregated states, and surface/interface structure manipulation, it elucidates how various levels of molecular modifications enhance solar cell efficiency through improved charge transfer, stability, and overall performance. This comprehensive exploration provides a detailed understanding of the complex relationship between molecular design and solar cell performance, discussing current advancements and potential future applications of these molecules in solar energy technology.

Green to deep-red emissive carbon dot formation by C+ion implantation on nitrogen beam created self-masked nano-template

We report the formation of green to red emissive arrays of carbon dot on silicon-nitride nano-templates by successive implantation of nitrogen and carbon broad ion beams. The patterned nano-templates are formed by 14 keV N2+ion-bombardment at grazing incident (70°) on Si. Subsequently, 5 keV C+ions are implanted at the selective sites of the pyramidal nano-template by taking advantage of the self-masking effect. The nano-pyramidal pattern and the implanted carbon dots at the specific sites are confirmed by atomic force microscopy and cross sectional transmission electron microscopy measurements. The developed carbon dots (CDs) are mostly amorphous and consists of SiC and graphitic nitrogen (CN). G-band and D-band carbons are identified by Raman spectroscopy, while the presence of SiC and CN are detected by XPS measurements. A change of band-gap is observed for C-implanted templates by the UV-vis spectroscopy. Excitation wavelength-dependent photoemission from the dots is found in the green to red region. Maximum intense PL is observed in the green-orange region for excitation wavelength of 425 nm and a redshift of PL with decreasing intensity is observed with the increase of excitation wavelength. The observed photoluminescence is described in terms of the combined effects of quantum confinement, graphitic nitrogen and defect induced additional states formation in the carbon dots. The potential applications of CDs are also addressed.

Spatially varying chemical phase formation on silicon nano ripple by low energy mixed ions bombardment

We report mixed (CO⁺and N₂⁺) ion beam induced spatially varying chemical phases formation on Si (100) surface in nanometer length scale. Simultaneous bombardment of carbon, oxygen and nitrogen like three reactive ions leads to well-defined ripple development and spatially varying periodic chemical phases formation. Post bombardment chemical changes of Si surface are investigated by x-ray photoelectron spectroscopy, and spatially resolved periodic variation of chemical phases are confirmed by electron energy loss spectroscopy. The thickness of ion modified amorphous layer, estimated by Monte Carlo simulation (SRIM), is in excellent agreement with the cross-sectional transmission electron microscopy measurements. The formation of such periodic nanoscale ripple having multiple chemical phases at different parts is explained in terms of chemical instability, local ion flux variation and difference in sputtering yield. Potential applications of such newly developed nano material are also addressed.

Stearic acid mediated growth of edge-on oriented bilayer poly(3-hexylthiophene) Langmuir films

The growth and structural evolution of stearic acid (SA) blended poly(3-hexylthiophene) [P3HT] Langmuir and Langmuir-Blodgett (LB) films were studied using complimentary surface and interface sensitive techniques to understand the possibility of ordering and layering of promising charge carrier mobility polymers, at the air-water interface and on the transferred solid substrate. SA-induced and subsequent compression-induced transitions in P3HT structure, from aggregated-3D to soft-2D and from in-plane mixed to unmixed layer, are evident at low and high pressures, respectively. The blending of SA molecules enhances the amphiphilic character of P3HT, which reduces the extent of the out-of-plane aggregation to form edge-on oriented (EO) bottom side-chain folded-bilayer (f-BL) islands (of size ~60 nm) within SA monolayer (ML), of commensurate thickness (~2.6 nm). Further compression, gradually rejects the less hydrophilic f-BL islands from the mixed layer to form EO P3HT BL islands (of coverage in-tune with starting composition) on top of SA ML. The formation of nearly covered P3HT(BL)/SA(ML) structured film on solid substrate is evident for the first time, which (even of limited P3HT thickness) has immense importance in the device properties, as the current in the bottom-gated organic thin-film transistors is known to travel only within few ML region near gate-dielectric.

Optomechanical switching of adsorption configurations of polar organic molecules by UV radiation pressure

Using photoemission spectroscopy (PES), we have systematically investigated the behavior of polar organic molecule, chloroaluminum phthalocyanine (ClAlPc), adsorbed in the Cl-down configuration on the Ag(111) substrate at low temperature − 195 °C under UV irradiation with a range of different photon fluxes. Judging from the evolution of photoemission spectral line shapes of molecular energy states, we discovered that the Cl atoms are so robustly anchored at Ag(111) that the impinging photons cannot flip the ClAlPc molecules, but instead they crouch them down due to radiation pressure; we observe that the phthalocyanine (Pc) lobes bend down to interact with Ag atoms on the substrate and induce charge transfer from them. As photon flux is increased, radiation pressure on the Pc plane initiates tunneling of the Cl atom through the molecular plane to turn the adsorption configuration of ClAlPc from Cl-down to an upheld Cl-up configuration, elucidating an optomechanical way of manipulating the dipole direction of polar molecules. Finally, work function measurements provide a distinct signature of the resulting upheld Cl-up configuration as it leads to a large increase in vacuum level (VL), ~ 0.4 eV higher than that of a typical flat-on Cl-up configuration driven by thermal annealing.