Improving All Ternary Small-Molecule Organic Solar Cells by Optimizing Short Wavelength Photon Harvesting and Exciton Dissociation based on a Bisadduct analogue of [70]PCBM as a Third Component Materials

Ternary small-molecule organic solar cells (OSCs) are efficiently optimized and fabricated with small-molecule benzodithiophene terthiophene rhodanine (BTR) as donors and blends of Y6 and bisPC71BM or PC71BM used as acceptors....

An ultrafast photodetector driven by interlayer exciton dissociation in a van der Waals heterostructure

We model interlayer exciton transport in van der Waals heterostructures to propose devices based on interlayer exciton dissociation in split-gate geometries for ultrafast photodetector applications.

Modeling of optical characteristics of organic solar cells based on poly (3,4-ethylene dioxythiophene): polystyrene sulfonate with incorporated silver nanoparticles

Changing the geometric parameters of the elements of the organic solar cell (OSC) and its components, changes in its optical characteristics such as reflection, absorption and transmission of light were studied. In the simulation, the main elements influencing the change in the characteristics of the OSC were poly (3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS), poly (3-hexylthiophene): [6,6] phenyl-C61butyric acid methyl ester (P3HT: PCBM) on silver nanoparticles. The dimensions of silver nanoparticles coincide with the thickness of the PEDOT layer (50 nm) in which they are located, the particle diameter is 45 nm, the thickness of the P3HT: PCBM layer has always remained equal to 100 nm. The peak at a wavelength of about 726 nm, when there are silver particles in the OSC, indicates the presence of localized surface plasmon resonance (LPPR), which causes a local amplification of the electromagnetic field near the surface of metal nanoparticles. LPPR induced by silver nanoparticles not only increases the degree of light absorption, but also enhances the degree of exciton dissociation. As a result, photocurrent and overall OSC efficiency can be significantly improved due to LPPR.

Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors

Engineering a low singlet-triplet energy gap (ΔEST) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a strong optical absorption (absorption coefficient = 3.8 × 105 cm−1) and a relatively large ΔEST of 0.2 eV. In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 μs), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a ~24 ns timescale and have an average electron-hole separation of ≥1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. Thus, access to these inter-CT states, which is possible even at low BF2 doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low ΔEST in organic DF emitters.

Influence of Temperature on Exciton Dynamic Processes in CuPc/C60 Based Solar Cells

Although the effect of high temperature on the performance of organic solar cells has been widely investigated, it is inevitably influenced by the associated annealing effect (which usually leads to film morphology change and variation in electrical properties), which makes the discussion more sophisticated. In this study, we simplified the issue and investigated the influence of low temperatures (from room temperature to 77 K) on the photocurrent and internal/external quantum efficiency of a CuPc/C60 based solar cell. We found that besides the charge dynamic process (charge transport), one or more of the exciton dynamic processes, such as exciton diffusion and exciton dissociation, also play a significant role in affecting the photocurrent of organic solar cells at different temperatures. Additionally, the results showed that the temperature had negligible influence on the absorption of the CuPc film as well as the exciton generation process, but obviously influenced the other two exciton dynamic processes (exciton diffusion and exciton dissociation).

Understanding of Photophysical Processes in DIO Additive-Treated PTB7:PC71BM Solar Cells

1,8-diiodooctane (DIO) additive is an important method for optimizing the morphology and device performance of polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7)-based polymer solar cells. However, the effect of DIO additive on charge photogeneration dynamics of PTB7-based polymer solar cells is still poorly understood. In this work, the effect of DIO additive on the carrier photogeneration dynamics, as well as device performance of PTB7: [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) solar cells was studied. Bias-dependent photoluminescence (PL) experiments of a neat PTB7 device show that the exciton cannot be dissociated by the electric field in the device within the operating voltage range, but it can be effectively dissociated by the high electric field. PL and time-resolved PL studies show that DIO additive reduces the phase size of PTB7 in the blend film, resulting in an increased exciton dissociation efficiency. The carrier recombination processes were studied by transient absorption, which shows geminate carrier recombination was suppressed in the DIO-treated PTB7:PC71BM device in ultrafast time scale. The increased exciton dissociation efficiency and suppressed carrier recombination in ultrafast time scale play an important role for DIO-treated PTB7:PC71BM solar cells to attain a higher power conversion efficiency.