Quantum Efficiency Of Generation Research Articles

Photorefractivity and photocurrent dynamics of triphenylamine-based polymer composites

The photorefractive properties of triphenylamine polymer-based composites with various composition ratios were investigated via optical diffraction, response time, asymmetric energy transfer, and transient photocurrent. The composite consisted of a photoconductive polymer of poly((4-diphenylamino)benzyl acrylate), a photoconductive plasticizer of (4-diphenylamino)phenyl)methanol, a sensitizer of [6,6]-phenyl-C61-butyric acid methyl ester, and a nonlinear optical dye of (4-(azepan-1-yl)-benzylidene)malononitrile. The photorefractive properties and related quantities were dependent on the composition, which was related to the glass transition temperature of the photorefractive polymers. The quantum efficiency (QE) of photocarrier generation was evaluated from the initial slope of the transient photocurrent. Transient photocurrents were measured and showed two unique peaks: one in the range of 10−4 to 10−3 s and the other in the range of 10−1 to 1 s. The transient photocurrents was well simulated (or reproduced) by the expanded two-trapping site model with two kinds of photocarrier generation and recombination processes and two different trapping sites. The obtained photorefractive quantity of trap density was significantly related to the photoconductive parameters of QE.

Photogeneration and excitons distribution function in organic bulk heterojunction solar cells

In this work, the excitons distribution function in organic bulk heterojunction solar cells, at a depth z has been determined from solving the charge continuity equation, by exploiting the Laplace transform with an appropriate boundary conditions. Next, the influence of the electron-hole pair separation distance on the excitons dissociation probability, the internal quantum efficiency and the binding energy, has been studied. The simulated results show that the probability density of the carriers photogenerated depend on the generation rate, excitons dissociation and the charge carriers in the cells. The potential improvement of the internal quantum efficiency of charge generation depends on electron-hole pair separation distance, the excitons dissociation probability into free charges and depends strongly on the optical absorption of the photons in the active layer.

Nanorod length-dependent photodriven H2 production in 1D CdS-Pt heterostructures.

Colloidal quantum confined semiconductor-metal heterostructures are promising candidates for solar energy conversion because their light absorbing semiconductor and catalytic components can be independently tuned and optimized. Although the light-to-hydrogen efficiencies of such systems have shown interesting dependences on the morphologies of the semiconductor and metal domains, the mechanisms of such dependences are poorly understood. Here, we use Pt tipped 0D CdS quantum dots (with ∼4.6nm diameter) and 1D CdS nanorods (of ∼13.8, 27.8, 66.6, and 88.9nm average rod lengths) as a model system to study the distance-dependence of charge separation and charge recombination times and their impacts on photo-driven H2 production. The H2 generation quantum efficiency increases from 0.2% ± 0.0% in quantum dots to 28.9% ± 0.4% at a rod length of 28nm and shows negligible changes at longer rod lengths. The half-life time of electron transfer from CdS to Pt increases monotonically with rod length, from 0.7 ± 0.1 in quantum dots to 170.2 ± 29.5ps in the longest rods, corresponding to a slight decrease in electron transfer quantum efficiency from 92% to 81%. The amplitude-weighted average lifetime of charge recombination of the electron in Pt with the hole in CdS increases from 4.7 ± 0.4 µs in quantum dots to 149 ± 34 µs in 28nm nanorods, and the lifetime does not increase further in longer rods, resembling the trend in the observed H2 generation quantum efficiency. Our result suggests that the competition of the charge recombination process with the hole removal by the sacrificial electron donor plays a dominant role in the observed nanorod length dependent overall light driven H2 generation quantum efficiency.

Solid-state synthesis of ZnS/ZnO nanocomposites and their decoration with NiS cocatalyst for photocatalytic hydrogen production

Herein was demonstrated the facile solid-state synthesis of ZnS/ZnO nanocomposites using planetary ball milling followed by subsequent thermal treatment. X-ray diffraction analysis has shown that the ZnS/ZnO products are nanocrystalline with an estimated crystallite size of less than 60 nm. A transmission electron microscope has demonstrated the presence of spherical heterostructures and core-shell structured ZnS/ZnO nanocomposites with the size being 40–80 nm in diameter. Fourier transform infrared spectroscopy analysis confirmed the presence of Zn–O and Zn–S bonds. The formation of a thin boundary between the ZnS and ZnO phases, where the sulfur oxidation state varies from −2 to +6, was determined by X-ray photoelectron spectroscopy. Degradation of methylene blue and Orange II organic dyes was used to assess the photocatalytic activity of ZnS/ZnO nanocomposites, and the nanocomposites of ZnS/ZnO, with a mass ratio of ∼1:1, demonstrated the highest visible light photocatalytic activity. For photocatalytic hydrogen production experiments, the surface of ZnS/ZnO nanocomposites was in situ decorated with NiS nanoparticles, where the mass content of NiS was 1.5%. The presence of NiS cocatalyst promotes the separation and transfer of photogenerated charges, thereby increasing the photocatalytic activity of ZnS/ZnO nanocomposites during hydrogen generation. The apparent quantum efficiency of photocatalytic hydrogen generation using ZnS/ZnO-3h-NiS photocatalyst was equal to 1.13%. This contribution shows the possibility to prepare nano-structured photocatalysts via mechanochemistry.

Construction of S-scheme Co3O4/g-C3N4 heterojunctions with boosted photocatalytic H2 production performance

The key step of photocatalytic technology using light energy to split water for hydrogen production is to prepare high performance and environmentally friendly stable photocatalysts. In this study, Co3O4 was loaded onto polymeric carbon nitride (PCN) to construct S-scheme heterojunctions by an impregnating method. The successful construction of S-scheme Co3O4/PCN heterojunctions was proved by the various characterizations, the constructed S-scheme Co3O4/PCN heterojunctions have favorable photoelectric effect and exhibit better H2 evolution performance than the single Co3O4 and PCN. Construction of S-scheme Co3O4/PCN heterojunctions can elevate active sites induced by N-deficient formation. Therein, 3% is the optimal molar ratio of Co/PCN, and the corresponding sample (3CoO/CN) exhibits the highest H2 evolution efficiency (105.06 μmol·g − 1·h − 1) via simulated solar light illumination for 4 h, which is about 41 folds higher than the single PCN (2.48 μmol·g − 1·h − 1). In short, the conspicuously boosted water splitting efficiency is mainly due to the strong light responsiveness and rapidly separation and migration of photoexcited charge pairs. The cyclic experiment results show that the S-scheme Co3O4/PCN heterojunction photocatalysts have high stability. The apparent quantum efficiency (AQE) of H2 generation on 3CoO/CN is 0.053% under 420 nm monochromatic light irradiation. This study strongly verifies that construction of S-scheme Co3O4/PCN heterojunctions is a feasible route to boost the photocatalytic activity of g-C3N4, providing an interesting reference for design highly efficient and environmentally friendly C3N4-based photocatalysts.

Plasma surface treatment facilitated visible light-driven H2 production over TiO2

TiO2 precursors were treated by plasma technology in three atmospheres (N2, Ar, H2). Interstitial N-doping can be facilely realized in N2 atmosphere, the light absorption range of N2-TiO2 is enlarged, and the surface oxygen vacancies (OVs) are significantly increased. Surface OVs enhance the efficient separation of photogenerated e−/h+ pairs in TiO2. The microscopic oxide layer on the surface of TiO2 is destroyed, bringing about Ti3+ defects and formation of more surface OVs in H2 and Ar atmosphere. Ti3+ defects, high concentration of surface OVs and the Ti3+-OVs defect energy level significantly reduce the photogenerated electron excitation energy. The photocatalytic H2 production activity of TiO2 treated via plasma technique in the different atmospheres was evaluated under visible light irradiation. Consequently, the H2 production efficiency on N2-TiO2 is 103.6 umolh−1 g−1, which is 2.1 times, 1.6 times, and 1.3 times of that on the pristine TiO2, H2-TiO2, and Ar-TiO2, respectively. The apparent quantum efficiency (AQE) of H2 generation on N2-TiO2 is 0.08%, which is 1.6 times of that over the reference TiO2 under 420 nm monochromatic light irradiation. The photocatalytic mechanisms for H2 production over all the photocatalysts were discussed according to a series of characterizations.

Effect of Material and Shape of Nanoparticles on Hot Carrier Generation

Nonradiative decay of photoexcited plasmons generates energetic nonthermal charge carriers. These hot charge carriers play a major role in plasmonic photocatalysis and photovoltaics. Therefore, establishing the relationship between the hot carrier generation efficiency and the structural and chemical parameters of nanoparticles is crucial for developing highly efficient plasmonic catalysts and photovoltaic materials. In this study, we compare the quantum efficiency of hot carrier generation between gold (AuNPs) and silver nanoparticles (AgNPs), and spherical (AuNSs) and cubic gold nanoparticles (AuNCs). We construct nanoparticle-on-mirror (NPoM) systems where reactant molecules are positioned in the nanogaps between the nanoparticles and gold films. Excitation of the NPoM at 785 nm, followed by the detection of products using surface-enhanced Raman spectroscopy allows us to measure the plasmon-driven reaction yields. Dividing the reaction yield by the calculated absorption cross section at the excitation laser wavelength provides the efficiency of hot carrier generation per absorbed photon. We reveal that AgNPs are more effective at generating hot carriers than AuNPs, which is consistent with the higher electron-surface scattering rate of AgNPs. The hot carrier generation of AuNCs is marginally better than that of AuNSs, which can be attributed to the enhanced electric fields inside the AuNCs in the nanogap region. This study contributes to a rational design of plasmonic catalysts or photovoltaic materials of higher efficiencies.

(Invited) Light Driven H2 Generation in Pt-Tipped CdS Nanorods: Dependence on the Pt Size and CdS Rod Length

Colloidal quantum confined semiconductor-metal nano-heterostructures are a promising class of photocatalysts for solar energy conversion. In these photocatalysts, the semiconductor domain serves as the light absorber and the metal as the catalyst. Such photocatalysts combine the superior light absorption and charge transport properties of the semiconductor with the superior catalytic activity and selectivity of the metal. Furthermore, both domains can be independently tuned to enhance the photocatalytic performance of the heterostructure. Among various semiconductor/metal heterostructures, metal-tipped colloidal semiconductor nanorods (such as CdS-Pt), have attracted extensive interest because they have been reported to have high quantum efficiencies of light driven H2 generation and their morphology can be systematically tuned. The overall light driven H2 generation process involves multiple elementary charge separation and recombination steps in the semiconductor and across the semiconductor/metal interface as well as proton-coupled electron transfer reactions at the catalytic center. The change of the semiconductor or metal domains can often have effects on multiple competing processes involved in the overall reaction. As a result of these complexities, the mechanisms for the morphological dependence of the observed H2 generation efficiencies are not fully understood, hindering the rational design of these photocatalysts. In this talk, we use Pt tipped CdS nanorods (CdS-Pt) as a model system to examine the effect of Pt size and CdS rod length on their light driven H2 generation efficiency. We show that increasing the Pt particle size increases the overall H2 generation quantum efficiency through both increasing the rate of electron transfer from the CdS to Pt and enhancing the efficiency of water/proton reduction; H2 generation efficiency increases at longer CdS rod length by suppression of charge recombination across the Pt/CdS interface. Our work demonstrates that through systematic in situ study of elementary processes involved in the overall H2 generation, it is possible to rationally design and improve semiconductor-metal hybrid photocatalysts.

Striking dual functionality of iron pyrite-graphene oxide nanocomposites in water treating and water splitting reactions

In this study, we report a simple one-pot solvothermal route of FeS2 (pyrite)/GO (graphene oxide) nanocomposites that exhibit outstanding physicochemical properties as efficient catalysts towards dual functionality of water treating and water-splitting applications. The FeS2/GO (FSG) nanocomposites of varying FeS2 to GO weight ratios were prepared and characterized for physicochemical properties. The introduction of GO mediated the morphology and structural properties to aligned FeS2 spherical nanoparticles within the GO network compared with pristine FeS2 cubical nanostructures. In water treatment applications, the synthesized FSG nanocomposite with FeS2 to GO ratio of 4:3 was highly effective for the complete degradation (∼99%), significant mineralization (>70%), and complete detoxification of antibiotic amoxicillin (AMCT) under the optimal solar-Fenton treatment when compared to bare FeS2, and other FSG nanocomposites. Radical scavenging experiments, leaching profile for iron (Fe) species (total Fe, Fe(II), and Fe(III)), decomposition profile of hydrogen peroxide, and HO• generation in the reaction medium helps to postulate the possible reaction mechanisms for AMCT degradation. The greatly enhanced catalytic performance of FeS2/GO was correlated with efficient recycling of Fe(II)/Fe(III), higher solar-light absorptivity due to the GO existence, and synergistic coupling of FeS2 and GO evidenced through the strong formation of Fe-O chemical bonds as confirmed by Fourier-transform infrared spectroscopy. Finally, the nanocomposites achieved enhanced apparent quantum efficiency for hydrogen generation through a water-splitting reaction. The reaction mechanism of FSG nanocomposite for water-splitting was proposed accordingly. Overall, this work could provide new insights for developing potential nanocomposite materials for widespread energy generation and environmental remediation applications.

Synthesis and in vitro evaluation of a novel thienopyrimidine with phototoxicity towards rat glioma F98 cells

Glioblastoma multiforme is one of the most aggressive cancer forms in humans, and has low recovery rates after surgery, ionizing radiation and chemotherapy. Therefore, there is a high interest in the development of new treatment methods, as for instance photodynamic therapy (PDT). It is here presented results of the cytotoxic properties of the novel compound N1-(4-(4-(benzyl(methyl)amino)thieno[2,3-d]pyrimidin-6-yl)benzyl)-N2,N2-dimethylethane-1,2-diamine (1), which was found ten-fold more active on the rat glioma cell model F98 than the reference drug Temozolomide (TMZ). Further cell survival studies showed a profound increase in F98 cell death on UVA-radiation (330 nm, 0.5 mW/cm2). Photochemical internalization induced delivery of compound 1, but in contrast to the cytostatic drug Bleomycin, a higher cytotoxicity was not observed. Localization studies using fluorescence microscopy revealed that compound 1 readily internalized into the cytosol but did not enter the cell nucleus. The compound was shown to be a relatively weak epidermal growth factor receptor inhibitor, which is not likely to explain its cytotoxicity. However, the quantum efficiency for generation of singlet oxygen was 23%, suggesting generation of reactive oxygen species as one possible mechanism. Although more studies are needed to reveal detailed mode of action, compound 1 is a promising photosensitizer candidate for further development in tests of animal models.

Spectroscopy of triplet-excited complexes of oxygen with spruce cone molecules extract from picea abies in AOT micelles under combined photoexcitation

The paper presents a method for obtaining an extract from the cones of Picea Abies spruce and fabrication a microemulsion based on it, which has an absorption spectrum in the UV region and luminescence in the red region (680-720 nm). A spectral study of a microemulsion with an extract containing polyphenols and phenolic acids (vanillic, protocatechuic, oxybenzoic) in the visible and IR spectral regions has been carried out. On the basis of time-resolved spectral data, the possibility of formation of reactive oxygen species, in particular, singlet oxygen, in a microemulsion under the action of UV radiation has been proved. A technique for oxygen saturation of microemulsions with an extract has been developed. The quantum efficiency of singlet oxygen generation upon absorption of light at a wavelength of 400 nm by an extract with different concentrations of molecular oxygen inside reverse micelles has been determined. It has been established that the quantum yield of singlet oxygen (1Δg) in a microemulsion with an extract can be increased by a factor of 9.5 and this value can be controlled by changing the oxygen accumulation time inside the micelle. It was found that with the oxygen concentration grow, both extract fluorescence intensity and optical density increase, and long-lived delayed fluorescence appears. A controlled concentration process of oxygen complexation with extract molecules accompanied by chemiluminescence in the red region of the spectrum has been studied. The rate constants of energy deactivation in the contact complex after photoexcitation during quenching of triplet states of the extract molecules have been determined

Hole utilization in solar hydrogen production.

In photochemical production of hydrogen from water, the hole-mediated oxidation reaction is the rate-determining step. A poor solar-to-hydrogen efficiency is usually related to a mismatch between the internal quantum efficiency of photon-induced hole generation and the apparent quantum yield of hydrogen. This waste of photogenerated holes is unwanted yet unavoidable. Although great progress has been made, we are still far away from the required level of dexterity to deal with the associated challenges of wasted holes and its consequential chemical effects that have placed one of the greatest bottlenecks in attaining high solar-to-hydrogen efficiency. A critical assessment of the hole and its related phenomena in solar hydrogen production would, therefore, pave the way moving forward. In this regard, we focus on the contextual and conceptual understanding of the dynamics and kinetics of photogenerated holes and its critical role in driving redox reactions, with the objective of guiding future research. The main reasons behind and consequences of unused holes are examined and different approaches to improve overall efficiency are outlined. We also highlight yet unsolved research questions related to holes in solar fuel production.

Pt Particle Size Affects Both the Charge Separation and Water Reduction Efficiencies of CdS-Pt Nanorod Photocatalysts for Light Driven H2 Generation.

Decreasing the metal catalyst size into nanoclusters or even single atom is an emerging direction of developing more efficient and cost-effective photocatalytic systems. Because the catalyst particle size affects both the catalyst activity and light driven charge separation efficiency, their effects on the overall photocatalytic efficiency are still poorly understood. Herein, using a well-defined semiconductor-metal heterostructure with Pt nanoparticle catalysts selectively grown on the apexes of CdS nanorods (NRs), we study the effect of the Pt catalyst size on light driven H2 generation quantum efficiency (QEH2). With the increase of the Pt catalyst size from 0.7 ± 0.3 to 3.0 ± 0.8 nm, the QEH2 of CdS-Pt increases from 0.5 ± 0.2% to 38.3 ± 5.1%, by nearly 2 orders of magnitude. Transient absorption spectroscopy measurement reveals that the electron transfer rate from the CdS NR to the Pt tip increases with the Pt diameter following a scaling law of d5.6, giving rise to the increase of electron transfer efficiency at larger Pt sizes. The observed trend can be understood by a simplified kinetic model that assumes the overall efficiency is the product of the quantum efficiencies of charge separation (including hole transfer, electron transfer, and hole scavenging) and water reduction steps, and for CdS-Pt NRs, the quantum efficiencies of electron transfer and water reduction steps increase with the Pt sizes. Our findings suggest the importance of improving the quantum efficiencies of both charge separation and catalysis in designing efficient semiconductor-metal hybrid photocatalysts, especially in the regime of small metal particle sizes.

One-Component Cationic Photoinitiators from Tunable Benzylidene Scaffolds for 3D Printing Applications

This paper describes a series of novel benzylidene scaffold-based iodonium salt one-component photoinitiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure–activity relationships were performed via quantum-chemical calculations and experimental tests. New salts can efficiently decompose under irradiation from UV to visible regions of the spectrum. The design of new iodonium salts is described, followed by a description of properties of photoinitiators prepared in this way. All presented salts were characterized in terms of their spectral properties (UV–vis spectroscopy), ability to photodecompose (steady-state photolysis), cationic polymerization of the vinyl monomer, and epoxide monomer photoinitiation (quantum efficiency of acid generation and real-time Fourier-transform infrared measurements) as well as their proposed application in 3D printing. New benzylidene iodonium salts can photoinitiate the polymerization of vinyl ethers and epoxy monomers under LED@365 and LED@405 irradiation. Investigated compounds can simultaneously initiate and monitor the polymerization process according to the change of fluorescence during the photocuring process. Formulations before photopolymerization do not exhibit fluorescence, during the photopolymerization process fluorescence is “turning on”. This phenomenon might be used to monitor photopolymerization in an “online” manner.

Modulated-photocurrent spectroscopy of single-crystal organic semiconductor rubrene with pristine and trap-dominated surfaces

High-performance, benchmark organic semiconductor rubrene is investigated by modulated-photocurrent (MPC) spectroscopy. In this technique, periodically modulated and steady-state photocarrier populations are simultaneously generated in the sample by two independent light beams, with the resultant photocurrent measured by a lock-in amplifier. The technique allows identifying a bandlike carrier motion (as opposed to incoherent hopping) as the dominant charge transport mechanism in this highly crystalline molecular semiconductor, in agreement with prior studies, yet without the need for fabrication of complex transistor devices. Moreover, MPC spectroscopy is used to determine the important parameters, such as the density of states for traps, their carrier capture coefficient, and attempt to escape frequency, as well as the quantum efficiency of photocarrier generation and the photocarrier mobility. The MPC spectroscopy is also shown to be able to discriminate charge transport at the surface of the crystal from that occurring in the bulk. The wealth of the thus obtained information is essential for our better understanding of the microscopic mechanisms governing photoconductivity in this class of materials.

Subpicosecond Charge Separation Time Scale at Graphene Quantum Dot Surface

Fast exciton–exciton annihilation occurring at a few 10s ps time scale possesses a potential hurdle to the successful utilization of a multiple exciton generation (MEG) process. MEG produces over 100% quantum efficiency of exciton generation and thereby a dramatic improvement in device performance. Successful implementation of MEG would require a faster charge separation than the exciton annihilation time. In this work we showed < 1 ps photoinduced electron transfer (PET) time scale at graphene quantum dot (GQD)/N,N-dimethylaniline (DMA) interface that would probably allow electron–hole separation much before it annihilates. Modern experimental techniques, including ensemble-based femtosecond fluorescence upconversion and single molecule sensitive fluorescence correlation spectroscopy (FCS), are employed for an in-depth study of PET kinetics. Former technique asserts the ultrafast nature of interfacial PET kinetics, while FCS reveals weak molecular interactions resulting in short-lived (∼4–6 μs) GQD-DMA complex formation in water. A few microseconds binding time allowed us to measure accurately the much faster (<1 ps) intrinsic PET time scale in GQD-DMA complex before it dissociates.

Influence of growth temperature of KTiOAsO4 single crystals on their physicochemical parameters and formation of domain structures

A potassium titanyl arsenate (KTiOAsO4, KTA) crystal 50 × 80 × 60 mm in size has been grown by upgraded Czochralski method from flux (TGGS) with a decrease in temperature from 900 to 770 °C during pulling. It is shown that the spectroscopic properties of the parts of KTA crystals grown at 900 and 770 °C are close, whereas the electrical conductivity of the low-temperature (770 °C) KTA part turned out to be an order of magnitude lower than that of the high-temperature part. Visualisation of the domain structure by second-harmonic generation microscopy revealed a more efficient domain intergrowth (throughout the sample) in the low-temperature KTA, which is important for forming a regular domain structure (RDS) in a KTA-based nonlinear optical element. It is established that the quantum efficiency of parametric generation of light in the RDS formed in low-temperature KTA is several times higher than in the case of high-temperature KTA. The results obtained are important for optimising RDS parameters.

Enhanced triplet state generation through radical pair intermediates in BODIPY-quantum dot complexes.

Generation of triplet excited states through radical pair intermediates has been extensively studied in molecular complexes. Similar schemes remain rare in hybrid structures of quantum dot-organic molecules, despite intense recent interest of quantum dot sensitized triplet excited state generation. Herein, we demonstrate that the efficiency of the intersystem crossing from the singlet to the triplet state in boron dipyrromethene (BODIPY) can be enhanced in CdSe quantum dot-BODIPY complexes through a radical pair intermediate state consisting of an unpaired electron in the quantum dot conduction band and that in oxidized BODIPY. By transient absorption spectroscopy, we show that the excitation of BODIPY with 650 nm light leads to the formation of a charge separated state by electron transfer from BODIPY to CdSe (with a time constant of 6.33 ± 1.13 ns), competing with internal conversion to the ground state within BODIPY, and the radical pair state decays subsequently by back charge recombination to generate a triplet excited state (with a time constant of 158 ± 28 ns) or the ground state of BODIPY. The overall quantum efficiency of BODIPY triplet excited state generation was determined to be (27.2 ± 3.0)%. The findings of efficient triplet state formation and intermediate radical pair states in this hybrid system suggest that quantum dot-molecule complexes may be a promising platform for spintronics applications.

Sensitivity of Sub-Bandgap External Quantum Efficiency Measurements of Solar Cells under Electrical and Light Bias

The measurement of the external quantum efficiency (EQE) for photocurrent generation at photon energies below the bandgap of semiconductors has always been an important tool for understanding phenomena such as charge photogeneration via tail and trap states. The shape of the subgap EQE can also reveal the subtle but important physics of inter- and intramolecular states that lay at the heart of charge photogeneration in molecular systems such as organic semiconductors. In this work, we examine the influence of optical and electrical noise on the sensitivity of EQE measurements under different electrical and optical bias conditions and demonstrate how to enhance the dynamic range to an unprecedented >100 dB. We identify and study several apparatus-and-device-related factors limiting the sensitivity including: the electrical noise floor of the measurement system; flicker and pick-up noise; probe light source stray light; the photon noise of the light bias source; the electrical noise of the voltage bias source; and the shunt-resistance-limited thermal and electrical shot noise of the device. By understanding and minimizing the influence of these factors we are able to detect EQE signals derived from weak subgap absorption features in both organic and inorganic solar cell systems at photon energies well below their bandgaps.

Measuring Energetic Disorder in Organic Semiconductors Using the Photogenerated Charge-Separation Efficiency

Quantifying energetic disorder in organic semiconductors continues to attract attention because of its significant impact on the transport physics of these technologically important materials. Here, we show that the energetic disorder of organic semiconductors can be determined from the relationship between the internal quantum efficiency of charge generation and the frequency of the incident light. Our results for a number of materials suggest that energetic disorder in organic semiconductors could be greater than previously reported, and we advance ideas as to why this may be the case.