Efficient Photon Harvesting Research Articles

Insight into light‐ and static‐electric‐field‐induced polarization on polaron‐pair dynamics in neat P3HT device: A transient‐absorption‐spectroscopy‐based study

AbstractWe have investigated the polaron‐pair dynamics following the excitation of vibrationally hot exciton states in organic semiconductor‐based optoelectronic devices to better understand the photophysical properties, which can help to improve the device performance. In our earlier work, published at ‘Phys. Chem. Chem. Phys., 2019,21, 21236‐21248’, we have investigated the role of the static electric internal and external fields on the polaron‐pair dynamics in a neat poly(3‐hexylthiophene‐2,5‐diyl) based device. From this, we have concluded that the polaron‐pair dissociates into charge carriers due to the internal field present inside the device and the dissociation process accelerates when an external electric field is also applied in reverse bias. Apart from the electric‐field‐induced dissociation process, we now have also been interested in the light‐ and electric‐field‐induced polarization effect on the polaron‐pair dynamics. For this, in the present study, we have used femtosecond transient absorption spectroscopy to investigate the polaron‐pair dynamics in a neat P3HT‐based device for different angles of incidence of the light with an additional variation of the static electric field. It is well‐known that thin‐film photovoltaics can be designed for improved angle‐dependent responsivity at specific angles and the photon harvesting efficiency depends on the incident angle of light. Internal electric fields together with the electric field of the incident light both influence the charge generation efficiency of the device, which is determined by the photophysical processes happening between electronic excitation and the formation of charge. The change of reflectivity due to the variation of incident angle and the effect of the electric‐field induced polarization make an overall impact on the polaron‐pair dynamics as demonstrated by our investigations.

Comparative optical analysis of GaAs nanostructures for photovoltaic applications using finite element method

In this manuscript, a thorough comparative analysis of six GaAs based nanostructures (hollow and solid) is performed on the basis of their optical performance. These nanostructures are known to exhibit excellent anti-reflection properties, owing to their ability to generate a broadband absorption spectrum through efficient photon harvesting. Using the Finite Element Method (FEM) of the commercially available COMSOL Multiphysics package, the absorption characteristics, optical short circuit current density (JSC), electric field and photogeneration rates of six different nanostructures namely concentric nanocylinder (CNCy), hollow concentric nanocylinder (HCNCy), inverted nanopencil (INPe), hollow nanopencil (HNPe), nanorod + nanohemisphere (NR + NHe), and hollow nanorod + hollow nanohemisphere (HNR + HNHe) are computed. The optical performance of these nanostructures is largely dependent on their geometrical parameters such as filling ratio (FR = Diameter/Period), spacing and structural dimensions. The optimized values of these parameters can play a vital role in capturing the optical resonance modes by the nanostructures to produce absorption enhancement. It has been observed that the nanostructures with base diameter of 240 nm, period in the range of 300–350 nm and FR of 0.8 exhibit better optical characteristics. Optical JSC and optical efficiency of 29.45 mA cm−2 and 42.26%, respectively for CNCy nanostructure with FR of 0.8 and diameter of 240 nm is the highest among all the nanostructures. The effect of the angle of incidence of the photons striking the nanostructures on the average absorptance in both Transverse Electric (TE) and Transverse Magnetic (TM) modes are also investigated. In addition to this, we have also computed the effective refractive index for all the nanostructures using Maxwell Garnett formula in order to estimate the surface anti-reflection characteristics of these nanostructures.

Hybrid silver/silver-oxide nanoparticles doped hole transport layer for efficient photon harvesting in organic solar cells

Hybrid silver/silver-oxide nanoparticles doped hole transport layer for efficient photon harvesting in organic solar cells

Ternary organic photovoltaic using long wavelength light absorption polymer as guest donor with enhance photovoltaic performance

Ternary organic photovoltaics (OPVs) are fabricated by PTQ10 as donor materials, Y6 as an acceptor, and PTB7-Th as a guest donor. The lowest unoccupied molecular orbital (LUMO) energy levels of PTB7-Th are deeper than those of PTQ10, and a cascade of LUMO energy levels is formed among the different device materials. The PTQ10:Y6 binary OPVs show an open-circuit voltage (VOC) of 0.870 V, which is relatively higher than that obtained for the ternary OPVs. The decrease in the VOC of the ternary OPVs is mainly ascribed to an upshift in the HOMO energy levels of the blend donor and a narrow energy bandgap. The short-circuit current density (JSC) for the ternary OPVs can be increased from 25.07 mA cm−2 to 26.60 mA cm−2 with a PTB7-Th content of up to 15 wt%, which is mainly attributed to efficient photon harvesting and reduced charge recombination. Therefore, these results indicate that JSC and PCE can be significantly enhanced by the incorporation of PTB7-Th into PTQ10:Y6 binary films despite a significant decrease in VOC.

Design and synthesis of glycopolymers for efficient photocatalytic hydrogen evolution

Saccharide-based homopolymers (PMDG and PMDM) and diblock copolymers with 9-vinylcarbazole (PNVK-b-PMDG and PNVK-b-PMDM) were synthesized by deacetylation of RAFT-generated corresponding acetyl-glucopyranoside and acetyl-maltose polymer segments. Synthesized polymers chemical structures were authenticated by spectroscopic methods. SEC investigational values of the polymers’ weight average molecular weights (Mw) were obtained in the orbit of 1849–11166 g/mol with 1.14–1.57 range polydispersity (Ð). The acetylated di-block copolymers exhibited higher thermal stability (Td5%: 265–274 °C) than the corresponding homopolymers (Td5%: 259–261 °C). The acetylated di-block copolymers showed higher Tg values (54–67 °C) than the corresponding deacetylated polymers (52 °C). The glycopolymers with hierarchical porous TiO2 (HPT) semiconductor photocatalyst exhibited relatively long lived charge carriers for efficient photon harvesting and enabling them to efficiently drive sacrificial H2 generation in aqueous NaOH under visible light. The hydrogen production rate gradually increased from 109 μmol g−1 h−1 to 881 μmol g−1 h−1 when the NaOH concentration was boosted from 1 M to 10 M using PNVK-b-PMDG as a sacrificial electron donor with HPT and platinum. The glucose-based PNVK-b-PMDG diblock copolymer exhibited higher hydrogen production of 881 μmol g−1 h−1 with an apparent quantum efficiency (AQY) of ∼ 2.15 % than the di-block from maltose (PNVK-b-PMDM) [730 μmol g−1 h−1, AQY: ∼1.78 %] in the presence of alkaline condition (aqueous NaOH, pH = 10). The pendant carbazole moieties of the diblock copolymers improved the efficiency of photocatalytic H2 production by facilitating interaction of free –OH groups of the glycopolymer segment with the HPT which provide significant increase in the reduction potential and decrease of the charge recombination. This work could lead to a more efficient photoreforming path of novel glycopolymer to harvest renewable H2 energy.

New wide band gap π-conjugated copolymers based on anthra[1,2-b: 4,3-b': 6,7-c''] trithiophene-8,12-dione for high performance non-fullerene polymer solar cells with an efficiency of 15.07 %

Developing efficient wide-bandgap copolymer donor materials to match with narrow bandgap non-fullerene acceptors is continuously ongoing for polymer solar cells. Herein, two new D-A copolymers are designed and synthesized by embedding the same anthra[1,2-b:4,3-b':6,7-c"] trithiophene-8,12-dione (A3T) acceptor unit and different donor units, i.e., BDTTZ ( P126 ) and BDTTh ( P127 ). These copolymers showed broad absorption from 350 to 680 nm and deeper HOMO energy level. We have used these two copolymers as donors and a narrow bandgap non-fullerene acceptor Y6 to prepare bulk heterojunction polymer solar cells (PSCs). After the optimization, P126 :Y6 and P127 :Y6 attained overall power conversion efficiency of 15.07% and 12.27%, respectively. The higher PCE for the P126 than P127 is associated with the more efficient photon harvesting and photogenerated excitons, balanced charge transport, and low energy loss. Our results may help to design new polymers with a deeper highest occupied molecular orbital level that will be well-matched with non-fullerene acceptors. • We have used the approach of weak donor and strong acceptor approach to design the D-A copolymers. • Two D-A copolymers were designed with same A3T acceptor and different donors, i.e., BDTTZ ( P126 ) and BDTTh (P127 ). • Both the copolymers showed deeper HOMO energy level to achieved high V OC . • P126 :Y6 and P127 :Y6 showed power conversion efficiency of 15.07% and 12.27%, respectively.

Improved UV sensitivity and charge transport in PTB7-Th:PC71BM solar cells doped with cadmium selenide quantum dots

CdSe QDs are incorporated into PTB7-Th:PC71BM organic solar cells, which convert the ultraviolet light to visible light to improve the photon harvesting efficiency and gather on the top of active layers and enhance the electron transport capacity.

Binary and Ternary Polymer Solar Cells Based on a Wide Bandgap D-A Copolymer Donor and Two Nonfullerene Acceptors with Complementary Absorption Spectral.

A new wide-bandgap conjugated D-A polymer denoted as P106 with a medium acceptor dithieno [2,3-e;3'2'-g]isoindole-7,9 (8H) (DTID) unit and strong 2-dodecylbenzo[1,2-b:3,4-b':6,5-b"]trithiophene (3TB) donor units shows an optical bandgap of 2.04 and highest occupied molecular orbital energy level of -5.56 eV. P106 is used as the donor and two nonfullerene acceptors-medium bandgap DBTBT-IC and narrow band Y18-DMO-are used as acceptors for the construction of binary and ternary bulk heterojunction polymer solar cells. The optimized polymer solar cells based on P106 : DBTBT-IC and P106 : Y18-DMO exhibit power conversion efficiencies of 11.76 % and 14.07 %, respectively. The short-circuit current density (22.78 mA cm-2 ) for the P106 : Y18-DMO device is higher than that for P106 : DBTBT-IC (18.56 mA cm-2 ) one, which could be attributed to the more photon harvesting efficiency of the P106 : Y18-DMO active layer. In light of the high short-circuit current densities and fill factors for the Y18-DMO based device and the high value of open circuit voltage of the DBTBT-IC based device, ternary polymer solar cells are fabricated by using ternary active layer (P106 : DBTBT-IC : Y18-DMO) and achieve a power conversion efficiency of 16.49 % with low energy loss of 0.47 eV.

Modulating photon harvesting through dynamic non-covalent interactions for enhanced photochemical CO2 reduction

Molecular transition metal complexes are widely explored in artificial photosynthetic redox catalysis due to their extraordinary properties. However, these catalysts generally suffer from the intrinsic thresholds of photon harvesting efficiency and spectrum response range, greatly limiting their further applications. Polypyridyl ruthenium (Ru) has been perceived as a paradigmatic photosensitizer in CO2 reduction systems but seldomly maneuvered. Herein, we develop a novel and practicable pseudo-supramolecular assembly at a molecular scale by conjugation with ultra-small nitrogen-doped carbon quantum dots (NCQDs) as ultraviolet-visible (UV–vis) light chromophore for enhanced photochemical conversion of CO2 to CO. The reversible self-assembly of NCQDs with Ru is driven by dynamic non-covalent π-conjugated and electrostatic interactions. Femtosecond transient absorption and time-resolved fluorescence decay spectra combined with control experiment results collaboratively demonstrate that vectorial photo-induced exciton cascade occurs by means of their unique photophysical properties in the as-assembled NCQDs/Ru dyad, enabling the superior photosensitized CO2 reduction performance in both homogeneous and heterogeneous systems. This work is expected to not only shed new light on the development of promising artificial light-harvesting systems but also promote the implementation of metal complex-based systems for photoredox-catalyzed reactions.

Asymmetric simple unfused acceptor enabling over 12% efficiency organic solar cells

High photovoltaic performance with cost-effective material synthesis and device fabrication are the prerequisite for commercialization of organic solar cells (OSCs). Herein, we conduct a systematic structure–property correlation study on unfused acceptors adopting different frameworks. Dithieno[3,2-b:2′,3′-d]pyrrole (DTP) based A-D1-D-D2-A asymmetric acceptor (DBT-4F) has been screened as a promising acceptor for high-efficient OSCs. Three DTP-based unfused acceptors display strong near-infrared absorption with narrow optical band gap (Egopt < 1.45 eV). Blends of DBT-4F with PBDB-T contribute a champion power conversion efficiency (PCE) of 12.14% due to better miscibility to form homogenous fibrous phase separation. To the best of our knowledge, the PCE is among the highest values for unfused acceptor based binary OSCs in the literature. The excellent performance of DBT-4F is revealed with more efficient photon-harvesting, higher and more balanced charge transport, and less charge recombination in the blends. Our work manifests the great potential of DTP based asymmetric unfused acceptor for developing high-efficient OSCs via rational molecular design.

Efficient Ternary Polymer solar cells based ternary active layer consisting of conjugated polymers and non-fullerene acceptors with power conversion efficiency approaching near to 15.5%

Ternary polymer solar cells employing two polymers (P2, PTB7-Th) and one non-fullerene small molecule acceptor (Y6) were constructed using a conventional structure. The PTB7-Th, P2 and Y6 exhibit complementary absorption spectra therefore, the ternary blend consists of these three can maximize the photon harvesting efficiency which is advantageous to boost of short circuit current density of polymer solar cell. After the optimization of the weight ratios between the two donors and keeping constant the weight concentration of acceptor and following solvent vapor annealing in THF for 40 s, P2:PTB7-Th: Y6 (0.3:0.7:1.5) based polymer solar cells attained the power conversion efficiency of 15.46%, superior to that for polymer solar cells based on binary active layers i.e., P2:Y6 (12.62%) and PTB7-Th:Y6 (12.84%), respectively. The open-circuit voltage for the P2:PTB7-Th:Y6 is about 0.88 V which is in between the values for P2:Y6 (0.94 V) and PTB7-Th:Y6 (0.85 V), consistent with the different highest occupied molecular orbital energy level for P2 (−5.38 eV) and PTB7-Th (−5.27 eV). The enhancement in the short circuit current may be associated with the broader absorption profile of the ternary active layer relative to binary counterparts while the enhanced value of fill factor may be originated from the balanced charge transport, suppressed recombination, and faster charge extraction.

Combined Theoretical & Experimental Approaches for Molecular Design of NIR Dyes for Dye-Sensitized Solar Cells Aiming Towards Improved Efficiency and Stability

Introduction: Since its inception and first report in 1991, dye sensitized solar cells (DSSCs) have got great attentions towards the realization of lost cost solar energy harvesting owing to easy fabrication, lower raw materials and aesthetic beauty. In the recent past, DSSCs came in to the lime light owing to their potential applications for efficient room light harvesting due to very good performance under low light intensity and highly suitable for building integrated photovoltaics due to color tunability in combination of the controllable transparency. State-of-art DSSCs exhibiting power conversion efficiency (PCE) >13% in spite efficient photon harvesting only in the visible wavelength region give a good hope for the further enhancement in the PCE by development and implementation of novel potential dyes having sensitivity near-infrared (NIR) wavelength region utilizing the existing state-of-art DSSC fabrication technologies developed in last two decades. Apart from enhancing the PCE, increasing the stability is inevitable for the commercialization of DSSCs and nature of the anchoring group of the sensitizers are expected to play a vital role by controlling efficiency of charge injection and binding strength on the mesoporous wide band gap semiconductor like TiO2. A series squaraine dyes (SQ) having same p-conjugated mother core but varying anchoring group has been designed and subjected to QC calculations in both of the ground and excited states using Gaussian program. In parallel, some of the potential sensitizers have also been synthesized and subjected to photo-physical investigation aiming towards the verification of the theoretically predicted results. Experimental: In this work, a series unsymmetrical squaraine dyes (SQ) bearing different anchoring groups (SQ-138-SQ-156) as shown in the Fig. 1 were logically designed and subjected to QC calculations. In order to construct theoretical energy band diagram, HOMO energy level was calculated after structural optimization using 6-311G/DFT/B3PW91 and PCM model using Ethanol solvent. Optimized structures were then used for TD/DFT excited state absorption spectral calculations and wavelength associated with the full width at half maximum of the spectrum was considered to be Eg followed by calculation of energy of LUMO by the relation LUMO = HOMO + Eg. Some of the designed dyes bearing different anchoring groups were synthesized, characterized and subjected to photo-physical investigation including the DSSC fabrication and characterizations. Results and Discussion: A perusal of the Fig. 1, clearly corroborates that except two dyes that is SQ-141 and SQ-146 bearing hydroxyl and catechol anchoring groups, all of the designed dyes seems to suitable as sensitizers for the fabrication DSSCs using TiO2 as mesoporous electron accepting scaffold and I-/I3 – redox electrolyte. In parallel to theoretical QC calculations, some of the potential dyes were also synthesized and subjected to their photo-physical characterization before their utilization for DSSC fabrication. Photo-physical results for some of the experimentally synthesized dyes indicate that there was only a difference of about 60-70 nm (0.06 eV) in λmax and (±0.06 eV) in Eg between theoretical prediction and experiment results. At the same time, experimental energy band diagram for four of the synthesized dyes as shown in the inset of Fig. 1, exhibits excellent match with the theoretical results. Rate of dye adsorption and their binding strength on the mesoporous TiO2 for some of the synthesized dyes was also investigated. It has been found that dye with Phosphonic acid anchoring group although exhibit nearly rate of dye adsorption as compared to that of one bearing carboxylic acid anchoring group but depicted >60 times higher binding strength. On contrary, it exhibited drastically hampered PCE than that of dye bearing –COOH, which has been explained by poor electron injection from the excited dye molecule to the conduction band of TiO2 owing to highly diminished intramolecular charge transfer and electronic coupling with d-orbitals of the TiO2 as indicated by QC calculations. One of the newly synthesized dye SQ-140 bearing cyanoacrylic acid anchoring, exhibited not only very good photo-voltaic performance with PCE of about 6 % after simulated solar irradiation but also NIR photosensitization having photon harvesting mainly between the 500 nm-800 nm with peak of the incident photon to current conversion efficiency of nearly 80 % at 700 nm. Acknowledgement: SSP would like to express sincere thank JSPS to Japan Society for Promotion of Science for the financial support by Grant-in-Aid for scientific research (C) [Grant No.-18K05300] to carry out the research. Figure 1

Achieving 17.4% Efficiency of Ternary Organic Photovoltaics with Two Well‐Compatible Nonfullerene Acceptors for Minimizing Energy Loss

AbstractA power conversion efficiency (PCE) of 16.2% is achieved in PM6:BTP‐4F‐12 based organic photovoltaics (OPVs). On the basis of efficient binary OPVs, a series of ternary OPVs are constructed by incorporating MeIC as the third component. The open circuit voltages (VOCs) of ternary OPVs can be gradually increased along with the incorporation of MeIC, suggesting the formation of an alloy state between BTP‐4F‐12 and MeIC with good compatibility. The energy loss (Eloss) of ternary OPVs can be decreased compared with that of two binary OPVs, contributing to the VOC improvement of ternary OPVs. The short circuit current density (JSC) and fill factor (FF) of ternary OPVs can also be simultaneously enhanced with MeIC content up to 10 wt% in acceptors, leading to 17.4% PCE of the optimized ternary OPVs. The JSC and FF improvement of ternary OPVs is thought to result from the optimized ternary active layers with more efficient photon harvesting, exciton dissociation and charge transport. The 17.4% PCE and 79.2% FF is among the top values of ternary OPVs. This work indicates that a ternary strategy is an emerging method to simultaneously minimize Eloss and optimize photon harvesting as well as improve the morphology of active layers for realizing performance improvement for OPVs.

Novel Cu2ZnSnS4/Pt/g-C3N4 heterojunction photocatalyst with straddling band configuration for enhanced solar to fuel conversion

In the context of efficient conversion of CO2 to high-value carbonaceous fuels, the development of photocatalysts for CO2 reduction having high solar-to-fuel energy efficiency with exceptional selectivity and long-term stability is the prime requisite of current research. Herein, we reported a novel straddling band configuration based Cu2ZnSnS4/Pt-integrated g-C3N4 heterojunction photocatalyst for CO2 reduction to carbonaceous fuels. The heterojunction photocatalyst exhibited an enhanced CO2 reduction with an average CO/CH4 yield rates of 17.351/7.961 μmolg−1 h−1, which is ∼3.31 and ∼5.56 folds higher than pristine g-C3N4. The comprehensive analysis of heterojunction photocatalyst exhibited synergetic effects owing to higher surface area, efficient photon harvesting due to CZTS and multiple charge-transfer pathways together with Z-scheme charge transfer. Moreover, the localized surface-plasmon-resonance (LSPR) and electron sink function of Pt led to an efficient interfacial charge carrier separation, surface site activation for CO2 reduction and in the consequence of that enhanced the photocatalytic performance.

Subtly adjusted active layer self‐assembly process for efficient organic solar cells

AbstractThe phase separation degree of active layers plays a vital role in enhancing the power conversion efficiency of organic solar cells. Two post treatments were employed to optimize the phase separation degree of active layers by subtly adjusting the self‐assembly process for SMPV1:PC71BM based active layers (SMPV1, 2,6‐bis[2,5‐bis(3‐octylrhodanine)‐(3,3‐dioctyl‐2,2':5,2''‐terthiophene)]‐4,8‐bis((5‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene; PC71BM, [6,6]‐phenyl‐C71‐butyric acid methyl ester). In this work, a power conversion efficiency of 7.93% was obtained for devices with an as‐cast active layer, which is close to the highest values reported for SMPV1 based devices. The power conversion efficiency was further increased to 8.64% or 8.99% for active layers with thermal annealing or thermal annealing together with solvent vapor annealing, respectively. The enhanced performance is mainly attributed to more efficient photon harvesting and charge transport induced by the post annealing treatment of the active layers. The face‐on molecular orientation of SMPV1 is increased for active layers with post annealing treatment, which is beneficial for charge transport along directions perpendicular to the substrate. This work further confirms the positive effect of post annealing treatment on the performance improvement of organic solar cells. © 2019 Society of Chemical Industry

Effects of physical orientation of dye molecules and molecular orbitals on performance of solid-state dye sensitized solar cells.

Performance of Dye-sensitized devices depends on the photon absorption and carrier injection properties of the sensitizer (dye). The orientation of the dye molecule affects the photon absorption cross-section, injection efficiency and carrier transport. These effects are studied, using three variants of cyanine dyes in n-TiO2/Dye/p-CuSCN heterojunction. The results show correlation of dye-molecule's orientation on the short-circuit-photocurrent (Isc). The open-circuit-voltage (Voc) is also subjective. The orientation of the dye molecule influence the photon-harvesting efficiency and obstruct the hole-conductor penetrating onto the working-electrode. Additionally, Cumulative effects of e-e, e-h, spin-coupling and HOMO/LUMO distribution are identified.

Improved performance of polymer solar cells by doping with Bi2O2S nanocrystals

Bismuth oxysulfide (Bi2O2S) has been demonstrated as a potential candidate for photovoltaic material because of favorite band gap (1.5 eV), effective charge dissociation, high carrier mobility, and long carrier lifetime. In this work, we synthesis the Bi2O2S nanocrystals by hydrothermal method, and incorporate Bi2O2S nanocrystals as a third component into poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b'] dithiophene-2,6-diyl] [3-fluoro-2-(2-ethylhexy) carbonyl] thieno [3,4-b] thiophenediyl]] (PTB7):acceptor [6,6]-pheny C71-butyric acid methy ester (PC71BM) binary polymer solar cells (PSCs). The results show that the power conversion efficiency (PCE) of ternary PSCs is obviously improved by 21.8% in comparison with binary PSCs (from 8.79% to 10.71%) by adding 1 wt% Bi2O2S nanocrystals. Introduction of Bi2O2S nanocrystals into the PTB7:PC71BM system can expand absorption range of sunlight in the PSCs, effectively enhance the crystallinity of PTB7 and optimize the surface morphology of photoactive layer, which leads to more efficient photon harvesting, enhances exciton dissociation, accelerates charge carrier transport and reduces charge recombination. Moreover, the addition of appropriate amounts of Bi2O2S nanocrystals into PTB7:PC71BM can effectively improve the lifetime of PSCs due to the improvement of crystallinity of PTB7. This work demonstrates the great potential use of bismuth compounds for photovoltaic devices fields.

Influence of nitrogen doping on TiO2 nanoparticles synthesized by pneumatic spray pyrolysis method

Improving the photon harvesting efficiency of dye sensitized solar cells (DSSCs) employing TiO2 photo-anode has been the major issue since 1991. So it is very important to discover new techniques that will enhance the properties of TiO2 nanoparticles (NPs) which will then prevent recombination of the photo-generated electron hole pairs and as well as improving the visible absorption properties of the TiO2. This will in turn improve the performance of the DSSC photo-electrode. The optical, electronic and structural properties of TiO2 NPs rely on factors like morphology, surface area, particle size and the presence of beneficial defects caused by dopants. This study focuses on the fabrication and characterization of nitrogen doped TiO2 (NPs) prepared by pneumatic spray pyrolysis (PSP) technique. The un-doped and nitrogen doped TiO2 NPs were prepared using titanium butoxide as a precursor and urea as the dopant. The morphological and structural properties of PSP synthesized NPs were evaluated using SEM, EDX, Raman Spectroscopy (RS), XRD and FTIR. SEM analysis revealed that the presence of nitrogen dopant results in a significant change in the surface morphology of the PSP synthesized NPs. RS revealed the presence of Raman vibrational modes and symmetry at 158 (Eg(1)), 208 (Eg(2)), 258 (B1g), 255 (B1g) 396 (B1g), 514 (A1g + B1g(2)) and 640 (Eg(3)) belonging to a mixed Anatase-Rutile phase. XRD analysis revealed that the PSP synthesized NPs have particles sizes of 10.90 nm, 11.31 nm, 11.93 nm and 14.14 nm for un-doped TiO2, 0.005 M TiO2, 0.015 M TiO2 and 0.025 M TiO2 NPs respectively. FTIR spectra of the PSP fabricated samples exhibited a peak at 616.22 cm−1 that is assigned to Ti–O vibrational stretching of the anatase phase of TiO2. UV–vis spectroscopy revealed a decrease in energy band gap with increase in dopant level for the TiO2 samples prepared.

Organic-inorganic hybrid Sn-based perovskite photodetectors with high external quantum efficiencies and wide spectral responses from 300 to 1000 nm

Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap (1.6 eV) limits their photon-harvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W−1, a specific detectivity of 7×1012 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of 350–900 nm, with a maximum value of about 80% at 550 nm.

Quadrupolar D–A–D diketopyrrolopyrrole-based small molecule for ternary blend polymer solar cells

A quadrupole diketopyrrolopyrrole (DPP)-based small molecule (DPP4T-Cz) was designed and synthesized to enhance absorption coefficient, and then employed as the third component to improve the light harvesting of polymer solar cells based on a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Because of an enhanced absorption coefficient of more than 105 cm−1, the photon harvesting efficiency was improved effectively in the near infrared (near-IR) range by using only a small amount of DPP4T-Cz (3.4 wt%) into the P3HT:PCBM binary blend polymer solar cells. Interestingly, the photocurrent generation was also enhanced in the visible range by the long-range energy transfer from P3HT to DPP4T-Cz molecules. As a result, the short-circuit current density (JSC) and power conversion efficiency (PCE) of P3HT:PCBM:DPP4T-Cz ternary blend devices were enhanced by more than 30% compared to those of P3HT:PCBM binary control devices. These findings suggest that quadrupole DPP-based molecules are one of the effective light-harvesting materials for ternary blend polymer solar cells.