Optical and Electronic Properties of Organic NIR-II Fluorophores by Time-Dependent Density Functional Theory and Many-Body Perturbation Theory: GW-BSE Approaches.

Organic-molecule fluorophores with emission wavelengths in the second near-infrared window (NIR-II, 1000-1700 nm) have attracted substantial attention in the life sciences and in biomedical applications because of their excellent resolution and sensitivity. However, adequate theoretical levels to provide efficient and accurate estimations of the optical and electronic properties of organic NIR-II fluorophores are lacking. The standard approach for these calculations has been time-dependent density functional theory (TDDFT). However, the size and large excitonic energies of these compounds pose challenges with respect to computational cost and time. In this study, we used the GW approximation combined with the Bethe-Salpeter equation (GW-BSE) implemented in many-body perturbation theory approaches based on density functional theory. This method was used to perform calculations of the excited states of two NIR molecular fluorophores (BTC980 and BTC1070), going beyond TDDFT. In this study, the optical absorption spectra and frontier molecular orbitals of these compounds were compared using TDDFT and GW-BSE calculations. The GW-BSE estimates showed excellent agreement with previously reported experimental results.

Optimal Fabrication of P3HT:PCBM Based Organic Solar Cells with N-Type DMDCNQI Dopant.

We have fabricated P3HT and PCBM-based organic photovoltaic cells using DMDCNQI as a guest dopant material and an n-type buffer layer. We have investigated the physical effects of the DMD-CNQI molecule as a guest dopant and an n-type charge transfer buffer layer on the performance of the device by examining measurements of light current-voltage and photoluminescence characteristics. The device using DMDCNQI as a dopant and a buffer layer exhibited a remarkable increase in short-circuit current density (Jsc) due to the ability of an electron acceptor and to the formation of a highly conducting charge transfer complex. In particular, the device consisting of ITO/PEDOT:PSS/P3HT:PCBM:DMDCNQI(1 wt%)/DMDCNQ/Al showed a maximum power conversion efficiency of 3.50%.

Synthesis and Characteristics of Fullerene Derivatives with Hexyl Perylene Moieties as N-Type Materials in Organic Solar Cells.

Recently, fullerene derivatives have received significant attention due to their potential impacts on the development of high performance organic photovoltaic (OPV) cells. One of the most successful fullerene derivatives thus far is [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM), which is being used as an electron acceptor material. However, PCBM has some disadvantages concerning its application in OPV cells, such as a weak absorption rate in the visible region and a relatively low LUMO level. In the present work, we synthesized a novel fullerene derivative, called hexyl perylene fullerene (HPF), which contains a hexyl perylene moiety. The HPF molecules showed two absorption peaks at 340 nm and 450 nm corresponding to the fullerene and to the perylene moiety, respectively. 1,8-octanedithiol was used as an additive to improve the compatibility between the poly(3-hexylthiophene) (P3HT) and the synthesized HPF The characteristics of an OPV cell composed of ITO/PEDOT:PSS/P3HT:HPF:1,8-octanedithiol/Al were investigated.

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.