Properties Of Organic Photovoltaic Cells Research Articles

5‐Bromosalicylaldehyde: Theoretical, Experimental and Spectroscopic (FT‐IR, Raman, H1and C13‐NMR, UV‐Vis) Studies and Their Photovoltaic Parameters

AbstractThis study aims to identify a 5‐bromosalicylaldehyde (5BSA) and assess its performance for application in organic solar cells. In the current work, the 5BSA was investigated using various techniques such as FT‐IR, Raman, NMR, and UV‐Vis spectroscopy to characterize the title molecule. The possible conformers of the 5BSA were studied using the MMFF methodology in Spartan software. The geometry optimization of modifications for each conformation was computed using the DFT approach for the B3LYP/6‐311++G(d,p) functional. The energy and dipole moment of most stable form were determined −1879057.42 kcal/mol and 1.455 Debye, respectively. The FT‐IR and Raman vibrational frequencies, the H1and C13NMR chemical shift values (in vacuum and in DMSO‐d6), the UV spectrum calculations (both in vacuum and in the solvent ethanol), the HOMO‐LUMO energy, and the map of MEP. Meanwhile, by considering the properties of organic photovoltaic cells, the open‐circuit voltage (VOC), hole reorganization energy (λh) and electron reorganization energy (λe), light‐harvesting efficiency (LHE), total reorganization energy (λtotal), the short‐circuit current density (Jsc), the driving force (ΔGinject), binding energy (Eb) were also computed for the title compound. In addition, transition density matrix (TDM) and density of states (DOS) analyses were conducted for the 5BSA molecule.

On the physical and photo-electrical properties of organic photovoltaic cells based on 1,10-Phenanthroline and 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphine non-fullerene thin films

The active layer of the bulk heterojunction organic photovoltaic cells is typically based on a polymeric blend containing a donor polymer and a fullerene-based polymer electron acceptor. However, in the last decade non-fullerene polymer-based solar cells have seen a rapid progress, due to their extraordinary chemical, thermal and photo stability, and because of their ability to decrease the voltage loss. The conventional Organic Photovoltaic Cells (OPVs), structures based on either P3HT:PCBM bulk heterojunction (BHJ) polymeric blend or P3HT/PCBM bilayer heterojunction, have limited efficiency and stability, in principal due to the fullerene derivatives used as acceptor component. PCBM for example, as many other fullerene derivatives, exhibits some deficiencies, such as: limited chemical and energetic tunability, small range of absorption spectra, morphological instability and relatively high production costs. That is why in the last years, novel non-fullerene materials started to be used in order to overcome the above limits associated with the fullerene acceptors. In this paper two different non-fullerene acceptor materials have been tested as potential candidates for the efficient OPVs based on P3HT donor polymer as main absorber: a new conjugated polymer containing chelating ligands like 1,10-Phenanthroline (Phen), and a small-molecule acceptor like 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphine (TPyP). For both cell configurations a decrease of the voltage loss was obtained, and it was also observed that the thickness of the P3HT donor layer has an important contribution to the output power (Pmax) and fill factor (FF) of the OPV structures (FF and Pmax increased almost two times by decreasing the thickness of the P3HT donor layer).

Influence of blend composition and annealing temperature on optical properties of organic photovoltaic cell based on P3HT:PCBM interpenetrating blend

ABSTRACTIn this paper, the influence of blend composition and annealing temperature on optical properties of organic photovoltaic (OPV) cells based on P3HT:PCBM interpenetrating blend is presented. Optical optimization of the OPV cell is first performed to determine the optimal geometry of the stack. The studied device structure is: glass/ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al. Simulation results give as optimized thicknesses: dPEDOT:PSS = 27 nm and dActive layer = 91 nm. The optimized OVP cell gives a short-circuit current JSC = 12.48 mA/cm2. The influence of technological parameters on the performance of the optimized P3HT:PCBM blend OPV cell is then clearly defined. Simulation results show that among the mass ratio of P3HT:PCBM blend active layers studied (1:1, 1:2, 2:1, 2:3 and 3:2), the active layer with the higher blend mass ratio (2:1) gives the best optical properties. Also, increasing the annealing temperature of the active layer leads to increase absorption. The blend active layer annealed at 140°C presents the best optical properties of the OPV cell.

The interface electronic properties of organic photovoltaic cells

The electronic properties of interfaces play a decisive role in determining the electrical characteristics of organic photovoltaic cells. In this paper, it is proposed that the mechanism responsible for the energy level alignment observed upon interface formation involves charge transfer between the electrode and the organic semiconductor. The amount of charges transferred is determined by occupying the density of states of the semiconductor according to Fermi–Dirac statistics and the observed energy level shifts are then governed by electrostatics. Within the proposed framework, we also discuss and numerically model the impact of the coupling strength between the molecular and the metal states. Photoelectron spectroscopy studies on two types of technologically relevant model interfaces, namely a metal/insulator/organic semiconductor heterojunction and a donor/acceptor heterojunction supported on a metal electrode, are then presented. The experimental observations, ranging from band bending to interface dipole formation, are shown to emerge naturally from the same theoretical framework. These results unambiguously demonstrate the essential role of the metal electrode in governing the energy level alignment, even significantly away from the metal surface.

Studies on the Properties of Organic Photovoltaic Cells Using TiOx and DMDCNQI as Double Buffer Layers.

Various types of n-type buffer layers have been used in organic electronic devices. These buffer layers turned out to expedite carrier injection and reduce series resistance, leading to good performance of organic electronic devices. In our current work, we have fabricated organic photovoltaic (OPV) cells consisting of ITO/PEDOT:PSS/P3HT:PCBM/TiOx/DMDCNQI/AI which were fabricated in the presence of air. To incorporate the individual advantages of each n-type buffer layer, a DMDCNQI and TiOx layers were inserted to act as n-type double buffer layers. This leads to an increase of short-circuit current (JSC) and fill factor (FF) with good stability, in comparison to P3HT:PCBM based conventional cells. The results imply that the structures of double buffer layers can provide possible alternative to achieving high performance and air durability.

Visualizing physical, electronic, and optical properties of organic photovoltaic cells

The most interesting active layer system for organic photovoltaic cells is the bulk heterojunction (BHJ). The general structure of a BHJ is a network of domains, which contain blended donor and acceptor molecules, often in pure and mixed phases. Directly visualizing this nanoscale phase separation of BHJs and corresponding morphological parameters has attracted much interest and has led to novel insights into their physical properties. Imaging methods that have been proven to be of great importance are scanning probe, scanning X-ray, and electron microscopy. Early works successfully employed conventional contrast mechanisms at high resolution for correlation of structure and function. Many imaging techniques also offer analytical capabilities using specific interactions of the probes with different material domains. Resulting material contrasts can be converted into morphological maps by correlation with the intrinsically different physical, electronic, and optical sample properties. Spatially resolved visualization of these properties is crucial to provide answers to questions about fundamental processes that determine the solar cell performance. A major paradigm shift was initiated by the discovery that instead of a completely separated network of donor and acceptor domains, a multiphase system is beneficial for enhanced photo-physical properties. Thereby phases differ in ordering, orientation and composition. In this review, we provide an overview of techniques and recent approaches for imaging BHJ structures at the nanoscale. Advantages and disadvantages of the underlying contrast mechanisms are summarized. In addition, we introduce best practices for the application of transmission electron microscopy (TEM) by comparing enhanced conventional and analytical modes.

Effect of the vertical composition gradient of active layer on the performance of bulk-heterojunction organic photovoltaic cell

A computational model is developed to investigate the effect of vertical composition gradient on the photovoltaic properties of organic photovoltaic cell based on poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). When the photovoltaic properties of model devices with systematic variation of vertical composition distribution are calculated by using this model, it is found that the efficiency increases almost linearly as the concentrations of P3HT and PCBM become richer near anode and cathode, respectively. The larger exciton generation near anode due to enrichment of P3HT near the anode contributes mainly to an increase of the device efficiency by compensating the lower hole mobility of P3HT with shorter pathway to the anode.

Simulation of physical properties of organic photovoltaic cell

We propose models of the incoherent optical absorption and exciton transport to simulate the processes of absorption and exciton diffusion in organic photovoltaic devices according to the optical principle and diffusion theory. The functional relation of optical absorption, and the power conversion efficiency versus the thickness of the film has been obtained. We demonstrate that the developed model can be useful for the modelling of the optical absorption and exciton separation in the optimization of devices of organic photovoltaic cells with high power conversion efficiency.