Search

The human retina perceives and preprocesses the spectral information of incident light, enabling fast image recognition and efficient chromatic adaptation. In comparison, it is reluctant to implement parallel spectral preprocessing and temporal information fusion in current complementary metal‐oxide‐semiconductor (CMOS) image sensors, requiring intricate circuitry, frequent data transmission, and color filters. Herein, an active‐matrix synaptic phototransistor array (AMSPA) is developed based on organic/inorganic semiconductor heterostructures. The AMSPA provides wavelength‐dependent, bidirectional photoresponses, enabling dynamic imaging and in‐sensor spectral preprocessing functions. Specifically, near‐infrared light induces inhibitory photoresponse while UV light results in exhibitory photoresponse. With rational structural design of the organic/inorganic hybrid heterostructures, the current dynamic range of phototransistor is improved to over 90 dB. Finally, a 32 × 64 AMSPA (128 pixels per inch) is demonstrated with one‐switch‐transistor and one‐synaptic phototransistor (1‐T‐1‐PT) structure, achieving spatial chromatic enhancement and temporal trajectory imaging. These results reveal the feasibility of AMSPA for constructing artificial vision systems. [ABSTRACT FROM AUTHOR]

Recently, much research has focused on the search for new mixed donor–acceptor layers for applications in organic electronics. Organic heterostructures with layers based on the generation 1 poly(propylene thiophenoimine) (G1PPT) dendrimer, N,N′-diisopropylnaphthalene diimide (MNDI), and a combination of the two were prepared and their electrical properties were investigated. Single layers of G1PPT and MNDI and a mixed layer (G1PPT:MNDI) were obtained via spin coating on quartz glass, silicon, and glass/ITO substrates, using chloroform as a solvent. The absorption mechanism was investigated, the degree of disorder was estimated, and the emission properties of the layers were highlighted using spectroscopic methods (UV–Vis transmission and photoluminescence). The effects of the concentration and surface topographical particularities on the properties of the layers were analyzed via atomic force microscopy. All of the heterostructures realized with ITO and Au electrodes showed good conduction, with currents of the order of mA. Additionally, the heterostructure with a mixed layer exhibited asymmetry in the current–voltage curve between forward and reverse polarization in the lower range of the applied voltages, which was more significant at increased concentrations and could be correlated with rectifier diode behavior. Consequently, the mixed-layer generation 1 poly(propylene thiophenoimine) dendrimer with N,N′-diisopropylnaphthalene diimide can be considered promising for electronic applications. [ABSTRACT FROM AUTHOR]

Organometallic halide perovskites have shown significant promise for applications in optoelectronics and photovoltaics in recent years. This research looks into the performance of bulk heterojunction-based photodetectors (PDs) based on the active layer of a CH3NH3PbI3:PCBM bulk heterojunction (BHJ). We assessed the impact of PCBM concentration in CH3NH3PbI3:PCBM BHJ on the electrical performance of the PDs. We found that the BHJ PD with a 4% PCBM concentration had the strongest capability to reject noise, as demonstrated by its superior ratio of photocurrent to dark current. Moreover, the PD with a 4% PCBM concentration in the active layer outperforms pristine CH3NH3PbI3-based PDs in terms of optoelectronic performance, showing greater responsivity and detectivity. The improved optoelectronic performance of BHJ PD is due to increased interfacial area, higher electron extraction and a decrease in traps and defects. The analysis of dark current–voltage curves reveals a significant reduction in charge recombination for BHJ devices, supporting the elimination of traps and defects by the inclusion of PCBM. The PD’s impedance study unveils that the incorporation of PCBM enhances charge transfer and effectively suppresses charge recombination, leading to enhanced optoelectronic performance. [ABSTRACT FROM AUTHOR]

Infrared (IR) optoelectronics have become important owing to their various applications, such as recognition, autonomous driving, and quantum communications. In particular, detection beyond 1400‐nm wavelength in the shortwave IR (SWIR) spectrum (i.e., 1550 nm) is important for eye safety, and long‐range communication. Recently, group III–V (InAs or InSb) colloidal quantum dots (CQDs) have attracted considerable interest due to their broadband optical tunability and toxic‐elements (Pb and Hg)‐free properties. Herein, a new approach is developed to synthesize highly monodispersed InSb CQD by employing the continuous injection method, which enables facile optical bandgap tuning at a SWIR wavelength of up to 0.9 eV. Furthermore, solution ligand exchange using halides and thiolates results in effective passivation of the InSb CQD surface and renders a stable p‐type CQD ink. Finally, bulk heterojunction (BHJ) structure is demonstrated using n‐type InAs:p‐type InSb CQDs, which exhibits broad absorption up to 1600 nm, and a sixfold higher responsivity compared with the pristine InSb CQD device due to the efficient charge transport in BHJ CQD solids. [ABSTRACT FROM AUTHOR]

Efficient in‐sensor computing necessitates linear, bidirectional, and centrosymmetric photoresponse weight updates; however, the realization of these attributes poses a persistent challenge, with most photosensor devices achieving linear analog weight updates while falling short of accomplishing bidirectional and centrosymmetric characteristics. Here, the development of a quantum dot (QD)–based bulk heterojunction synaptic transistor (QBST) with multi‐factor modulation through surface ligand engineering of blend QDs is reported. By controlling the charge transmission between QDs and the semiconductor, the QBST device enables tunable fading memory, which transforms linear weight updates in short‐chain devices into linear, bidirectional, and unprecedented centrosymmetric optical synaptic responses in long‐chain devices. Moreover, through the synergy of chemical and electric factors, the convolutional kernel of QBSTs‐based convolutional neural network realizes enhanced recognition for complex noisy fashion‐costume images, achieving an impressive 90.3% accuracy in the long‐chain device, highlighting the efficiency of centrosymmetric weight updates. The results demonstrate that surface ligand engineering offers a promising approach for customizable synaptic modulation, facilitating energy‐ and time‐efficient in‐sensor computing. [ABSTRACT FROM AUTHOR]

In this work, pristine calcium titanate (CaTiO3), polyaniline (PANI), binary PANI@carbon black (CB), and ternary PANI@CB/CaTiO3 composites were synthesized using solid-state and in situ oxidative polymerization method. XRD, FTIR, UV–Vis, PL, FE-SEM, and EDX analyses were studied in order to examine the structural, optical, and morphological properties of all grown samples. XRD, FTIR, FESEM, and EDX findings confirmed the formation of successful chemical organization among PANI, CaTiO3, and CB. The UV–Vis and PL investigation reaffirmed the reduction in optical band gap (2.67 eV–2.56 eV) and charge carrier recombination process due to inclusion of CaTiO3 into CB-reinforced polymer matrix. In photocatalytic experiment, PANI@CB/10%CaTiO3 catalyst showed efficacious performance to degrade the synthetic dyes (99.7% MO and 97.8% MB) after 120-min sunlight irradiation with higher rate and superb stability up-to 5th cycle against MO dye. In kinetic examination, pseudo-first-order kinetic model was obeyed by both dyes. Herein, the bulk heterojunction (BHJ) photovoltaic cell was fabricated by spin-coating the grown samples on FTO glass substrate and thermally evaporating the Al electrode subsequently. The BHJ fabricated by PANI@CB/10%CaTiO3 showed better efficiency (0.541%), photocurrent density (Jsc) (4.21 mA/cm2), and open-circuit voltage (Voc) (0.39 V). [ABSTRACT FROM AUTHOR]

With continuous innovation in organic photovoltaic materials, the power conversion efficiency （PCE） of organic photovoltaic （OPV） cells has approached 20%. The development of polymer donors and small molecule acceptors is considered crucial for improving the PCE of OPV cells. Among numerous donor materials, wide bandgap（WBG）polymer donors have dominated the OPV donor material field due to their excellent optoelectronic properties. To further enhance the photovoltaic efficiency of OPV, it is necessary to summarize and elucidate the correlation between the molecular structure and optoelectronic properties of WBG polymer donors. Firstly, this review summarize the methods for controlling the optical bandgap and molecular energy levels of polymer donors. Secondly, we explore and summarize the methods for controlling aggregation behavior of the polymer in solution and their correlation with their bulk heterojunction morphology. Thirdly, we emphasize the importance of reducing the energy losses in OPV cells and discuss methods to reduce these losses. Fourthly, we summarize the-state-of-the-art wide bandgap polymer donors. Finally, we discuss the opportunities and challenges for commercializing non-fullerene OPV cells based on WBG polymer donors. [ABSTRACT FROM AUTHOR]

Two kinds of polymer solar cells (PSCs) were fabricated with polymer donor PM6 and small molecule non‐fullerene acceptor L8‐BO as accepted based on bulk heterojunction (BHJ) or layer‐by‐layer (LbL) structure. The power conversion efficiency (PCE) of 18.43 % and 17.84 % can be achieved from the PSCs based on BHJ and LbL structure, respectively. Two kinds of PSCs exhibit the same open circuit voltage (VOC) of 0.88 V, which can be well explained from the same donor and acceptor materials and the same electrodes. The LbL based PSCs exhibit a relatively large short circuit current density (JSC) of 26.97 mA cm−2 and fill factor (FF) of 77.64 % in comparison with JSC of 26.64 mA cm−2 and FF of 76.07 % for BHJ based PSCs. The relatively high PCE of LbL based PSCs should be attributed to the sufficient exciton dissociation and charge collection efficiency, as well as the more balanced charge transport, which can be confirmed from the photogenerated current density dependence on the effective bias. This work demonstrates that layer‐by‐layer structure may have great potential in preparing highly efficient PSCs. [ABSTRACT FROM AUTHOR]

Abstract The human retina perceives and preprocesses the spectral information of incident light, enabling fast image recognition and efficient chromatic adaptation. In comparison, it is reluctant to implement parallel spectral preprocessing and temporal information fusion in current complementary metal‐oxide‐semiconductor (CMOS) image sensors, requiring intricate circuitry, frequent data transmission, and color filters. Herein, an active‐matrix synaptic phototransistor array (AMSPA) is developed based on organic/inorganic semiconductor heterostructures. The AMSPA provides wavelength‐dependent, bidirectional photoresponses, enabling dynamic imaging and in‐sensor spectral preprocessing functions. Specifically, near‐infrared light induces inhibitory photoresponse while UV light results in exhibitory photoresponse. With rational structural design of the organic/inorganic hybrid heterostructures, the current dynamic range of phototransistor is improved to over 90 dB. Finally, a 32 × 64 AMSPA (128 pixels per inch) is demonstrated with one‐switch‐transistor and one‐synaptic phototransistor (1‐T‐1‐PT) structure, achieving spatial chromatic enhancement and temporal trajectory imaging. These results reveal the feasibility of AMSPA for constructing artificial vision systems.

Ternary organic solar cells contain a single three-component photoactive layer with a wide absorption window, achieved without the need for multiple stacking. However, adding a third component into a well-known binary blend can influence the energetics, optical window, charge carrier transport, crystalline order and conversion efficiency. In the form of binary blends, the low-bandgap regioregular polymer donor poly(3-hexylthiophene-2,5-diyl), known as P3HT, is combined with the acceptor PC61BM, an inexpensive fullerene derivative. Two different non-fullerene acceptors (ITIC and eh-IDTBR) are added to this binary blend to form ternary blends. A systematic comparison between binary and ternary systems was carried out as a function of the thermal annealing temperature of organic layers (100 °C and 140 °C). The power conversion efficiency (PCE) is improved due to increased fill factor (FF) and open-circuit voltage (Voc) for thermal-annealed ternary blends at 140 °C. The transport properties of electrons and holes were investigated in binary and ternary blends following a Space-Charge-Limited Current (SCLC) protocol. A favorable balanced hole–electron mobility is obtained through the incorporation of either ITIC or eh-IDTBR. The charge transport behavior is correlated with the bulk heterojunction (BHJ) morphology deduced from atomic force microscopy (AFM), contact water angle (CWA) measurement and 2D grazing-incidence X-ray diffractometry (2D-GIXRD). [ABSTRACT FROM AUTHOR]

Photoinduced intermolecular charge transfer (PICT) determines the voltage loss in bulk heterojunction (BHJ) organic photovoltaics (OPVs), and this voltage loss can be minimized by inducing efficient PICT, which requires energy‐state matching between the donor and acceptor at the BHJ interfaces. Thus, both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT. In this study, an effective method for quantifying the hot state matching of OPVs was developed. The degree of energy‐state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor (MF) calculated from the modified optical density of the BHJ. Furthermore, the correlation between the open‐circuit voltage (Voc) of the OPV device and energy‐state matching at the BHJ interface was investigated using the calculated MF. The OPVs with small absolute MF values exhibited high Voc values. This result clearly indicates that the energy‐state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs. Because the MF indicates the degree of energy‐state matching, which is a critical factor for suppressing energy loss, it can be used to estimate the Voc loss in OPVs. [ABSTRACT FROM AUTHOR]

In recent times, solar energy has become one of the largest available sources of renewable energy at our disposal. However, the design of highly efficient solar cells is increasingly becoming crucial as there has been a surge for economically viable alternative energy sources with the lowest cost. Significant advances have been made through different routes to make photovoltaic (PV)/solar technologies economically viable, eco-friendly and consequently scalable. As a result, cellulose nanomaterials have become one of the emerging technologies in this regard because of the advantages of high-value bio-based nanostructured materials, such as their abundance and sustainability. Nanocellulose-based photoactive nanocomposite materials can be made by integrating conducting photoactive and electroconductive materials with hydrophilic biocompatible cellulose. Inorganic nanoparticles, such as graphene/reduced graphene oxide cadmium sulphide quantum dots, amongst others, can be introduced into the nanocellulose matrix and can be applied either as charge transporters or photoactive materials in different types of solar cells. Thus, in this review, we highlight the optoelectronic properties of different photoactive materials, particularly nanocellulose-based graphene nanocomposites; their efficiencies and drawbacks were X-rayed. The effect of doping each PV material on the PV performance is also discussed. It is anticipated that the novel material would result in a reduction in the cost of solar cells, jointly enhancing their efficacy in generating environmentally friendly electricity. Since the fabrication techniques and equipment play a crucial role in the development of solar cells, the fabrication techniques of bulk-heterojunction (BHJ) cells containing a nanocellulose-based graphene composite and case studies of already fabricated BHJ PV cells with nanocellulose-based graphene composite are discussed. [ABSTRACT FROM AUTHOR]

The bulk-heterojunction (BHJ) system that uses a π -conjugated polymer as an electron donor, and a fullerene derivative as an electron acceptor, is widely used in organic solar cells (OSCs) to facilitate efficient charge separation and extraction. However, the conventional BHJ system still suffers from unwanted phase segregation caused by the existence of significant differences in surface energy between the two BHJ components and the charge extraction layer during film formation. In the present work, we demonstrate a sophisticated control of fast film-growth kinetics that can be used to achieve a uniform distribution of donor and acceptor materials in the BHJ layer of OSCs without undesirable phase separation. Our approach involves depositing the BHJ solution onto a spinning substrate, thus inducing rapid evaporation of the solvent during BHJ film formation. The fast-growth process prevents the fullerene derivative from migrating toward the charge extraction layer, thereby enabling a homogeneous distribution of the fullerene derivative within the BHJ film. The OSCs based on the fast-growth BHJ thin film are found to exhibit substantial increases in JSC, fill factor, and a PCE up to 11.27 mA/cm2, 66%, and 4.68%, respectively; this last value represents a remarkable 17% increase in PCE compared to that of conventional OSCs. [ABSTRACT FROM AUTHOR]

This work studied a series of infrared detectors comprised of organic bulk heterojunctions to explain the origin of their broadband spectral response from the visible to the infrared spanning 1 to 8 μm and the transition from photonic to bolometric operation. Through comparisons of the detector current and the sub-bandgap density of states, the mid- and long-wave infrared response was attributed to charge trap-and-release processes that impact thermal charge generation and the activation energy of charge mobility. We further demonstrate how the sub-bandgap characteristics, mobility activation energy, and effective bandgap are key design parameters for controlling the device temperature coefficient of resistance, which reached up to -7%/K, better than other thin-film materials such as amorphous silicon and vanadium oxide.

In this paper, a novel structure of multilayer organic photovoltaic cell has been designed and simulated. The integration of Poly(3-hexylthiophene-2,5-diyl) (P3HT) buffer layer and Poly(9,9-bis(3’-(N,N-dimethyl) N- ethylammoinium propyl-2,7-fluorene)-alt-2,7-(9,9 dioctyl fluorene)) dibromide (PFN:BR) electron transport layer (ETL) in the proposed solar cell has improved the performance significantly. The various performance measuring parameters like power conversion efficiency (PCE), short circuit current (Jsc), open circuit voltage (Voc), fill factor (FF), quantum efficiency (QE) have improved significantly. Furthermore, the effect of different layer thickness, the density of traps $N_{t}$ and temperature on the proposed solar cell has been studied and the optimum value has been obtained. It has been observed that after optimizing the different parameters of the proposed structure, the performance measuring parameters shows an improvement of 14%, 33.3%, 200% and 300% in Voc FF, Jsc and PCE respectively over the reported organic solar cells. Further, a QE of about 90% is achieved in the proposed structure.

Recently, much research has focused on the search for new mixed donor–acceptor layers for applications in organic electronics. Organic heterostructures with layers based on the generation 1 poly(propylene thiophenoimine) (G1PPT) dendrimer, N,N′-diisopropylnaphthalene diimide (MNDI), and a combination of the two were prepared and their electrical properties were investigated. Single layers of G1PPT and MNDI and a mixed layer (G1PPT:MNDI) were obtained via spin coating on quartz glass, silicon, and glass/ITO substrates, using chloroform as a solvent. The absorption mechanism was investigated, the degree of disorder was estimated, and the emission properties of the layers were highlighted using spectroscopic methods (UV–Vis transmission and photoluminescence). The effects of the concentration and surface topographical particularities on the properties of the layers were analyzed via atomic force microscopy. All of the heterostructures realized with ITO and Au electrodes showed good conduction, with currents of the order of mA. Additionally, the heterostructure with a mixed layer exhibited asymmetry in the current–voltage curve between forward and reverse polarization in the lower range of the applied voltages, which was more significant at increased concentrations and could be correlated with rectifier diode behavior. Consequently, the mixed-layer generation 1 poly(propylene thiophenoimine) dendrimer with N,N′-diisopropylnaphthalene diimide can be considered promising for electronic applications.

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. Herein, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5‐trifluorobenzene, hexafluorobenzene, 1,3,5‐tribromo‐2,4,6‐trifluorobenzene (TFTB), 1,3,5‐tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz‐F:PM6:L8‐BO system. [ABSTRACT FROM AUTHOR]

As an emerging earth‐abundant light harvesting material, antimony selenosulfide (Sb2(S,Se)3) has received tremendous attention for photovoltaics. Manipulating the carrier separation and recombination processes is critical to achieve high device efficiency. Compared to the conventional planar heterojunction (PHJ), the bulk heterojunction (BHJ) configuration affords great potential to enable efficient charge extraction. In this work, BHJ Sb2(S,Se)3 solar cells are constructed based on CdS nanorod arrays (NRAs). Highly ordered CdS NRAs with appropriate nanorod lengths and diameters are obtained by regulating the growth environment and screening different substrates for CdS deposition. A low‐temperature oxygen doping strategy implemented on CdS NRAs is further developed to improve the optoelectronic and defect properties as well as form a favorable cascade band structure for CdS NRAs, so as to realize more efficient charge extraction and suppressed recombination at the heterointerface. As a result, the CdS NRAs‐based superstrated BHJ Sb2(S,Se)3 solar cell yields a considerable power conversion efficiency of 8.04%, outperforming that of the PHJ device. A careful comparative study of PHJ and BHJ based on electrostatic field simulations indicates that the BHJ allows more efficient charge extraction and transport. This work highlights the great potential of BHJ configuration for constructing high‐performance antimony chalcogenide solar cells. [ABSTRACT FROM AUTHOR]

Fluorinated multi-walled carbon nanotubes are implemented as the third component of the active layer of organic solar cells. The addition of approximately 1% weight fraction of these nanotubes into PCDTBT/PC60BM polymer/fullerene active layer leads to a noticeable increase in the main photovoltaic parameters of the solar cells, including their stability. Presumably, the origins of this influence are optimizing the donor/acceptor composite morphology and reinforcing its structure with fluorinated multi-walled carbon nanotubes. This hypothesis is supported by the dramatic influence of the fluorinated multi-walled carbon nanotube additive on the kinetics of the decay of the EPR signal of light-induced charges in the PCDTBT/PC60BM composite. [ABSTRACT FROM AUTHOR]

The composites based on a semiconducting polymer and a modified fullerene were deposited as active layers of organic photovoltaic cells (OPCs). Fluorinated carbon nanotubes were added into the composite according to the procedure described previously [Kobeleva, E.S. et al., Fuller. Nanotub. 31, 464 (2023)]. The admixture inhibited photodegradation processes within OPC samples. This phenomenon is due to several reasons, in particular, the fixation of the optimal nanostructure of the bulk polymer : fullerene heterojunction and inhibition of the processes of morphological degradation of the active layer. [ABSTRACT FROM AUTHOR]

Abstract Photoinduced intermolecular charge transfer (PICT) determines the voltage loss in bulk heterojunction (BHJ) organic photovoltaics (OPVs), and this voltage loss can be minimized by inducing efficient PICT, which requires energy‐state matching between the donor and acceptor at the BHJ interfaces. Thus, both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT. In this study, an effective method for quantifying the hot state matching of OPVs was developed. The degree of energy‐state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor (MF) calculated from the modified optical density of the BHJ. Furthermore, the correlation between the open‐circuit voltage (Voc) of the OPV device and energy‐state matching at the BHJ interface was investigated using the calculated MF. The OPVs with small absolute MF values exhibited high Voc values. This result clearly indicates that the energy‐state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs. Because the MF indicates the degree of energy‐state matching, which is a critical factor for suppressing energy loss, it can be used to estimate the Voc loss in OPVs.

Charge recombination is one of the critical factors that influences the performance of thin film polymer solar cells (TFPSCs). In this investigation, metal, plasmonic nano-particles are employed to suppress charge recombination and energy loss in TFPSC. Trimetallic nano-composite (NC) was successfully synthesized and composed of copper, nickel, and silver (Cu/Ni/Ag) using wet chemistry. The NC was incorporated into polymer-based solar absorber layers at different concentrations. The absorber layer is a fullerene-based bulk-heterojunction design using poly-3-hexylthiophene (P3HT) donor polymer. The results show that the power conversion efficiency of the device doped with NC has improved by 85% compared to the undoped one. The incorporation of tri-metallic NC into the polymer blend solar absorber resulted in enhanced optical absorption and improved collection of photo-current as reflected by the recorded high short circuit current density (J s c ) and fill factor. The enhancement of the performance is due to the occurrence of local surface plasmon resonances in the polymer medium. The experiment indicated that there is some increment in an open circuit voltage, which is attributed to the low energy losses as a result of improved exciton dissociation, charge carrier transport, and collection. [ABSTRACT FROM AUTHOR]

Organic materials are known for their variety of molecules. Methods to predict the parameters of organic photovoltaic (OPV) cells are required to avoid the time- and resource-consuming processes of manufacturing and testing OPVs. Usually, the open-circuit voltage (Uoc) is estimated as the difference between the ionization energy level of the electron donor molecule (Id) and the electron affinity level of the electron acceptor molecule (EAa). Various measurement methods are used to determine the energy level values of pure materials, which, when combined with energy level shifts due to the donor:acceptor interactions, make these estimations less precise. In this work, photoconductivity measurements were applied to the donor:acceptor films. Near threshold energy, the electron can be directly transferred from the donor to the acceptor molecule. The obtained charge transfer energy (ECT) shows the difference between Id and EAa in the film. This difference was compared to the Uoc value of an OPV made of the same donor:acceptor combination. We show that this approach provides less scattered results and a higher correlation coefficient compared to the Uoc estimation using energy level values. [ABSTRACT FROM AUTHOR]

The bulk-heterojunction (BHJ) system that uses a π-conjugated polymer as an electron donor, and a fullerene derivative as an electron acceptor, is widely used in organic solar cells (OSCs) to facilitate efficient charge separation and extraction. However, the conventional BHJ system still suffers from unwanted phase segregation caused by the existence of significant differences in surface energy between the two BHJ components and the charge extraction layer during film formation. In the present work, we demonstrate a sophisticated control of fast film-growth kinetics that can be used to achieve a uniform distribution of donor and acceptor materials in the BHJ layer of OSCs without undesirable phase separation. Our approach involves depositing the BHJ solution onto a spinning substrate, thus inducing rapid evaporation of the solvent during BHJ film formation. The fast-growth process prevents the fullerene derivative from migrating toward the charge extraction layer, thereby enabling a homogeneous distribution of the fullerene derivative within the BHJ film. The OSCs based on the fast-growth BHJ thin film are found to exhibit substantial increases in JSC, fill factor, and a PCE up to 11.27 mA/cm2, 66%, and 4.68%, respectively; this last value represents a remarkable 17% increase in PCE compared to that of conventional OSCs.

In the past decade, considerable efforts have been made to develop semi-transparent organic solar cells (ST-OSCs). Different materials and architectures were examined with the aim of commercializing these devices. Among these, the use of ternary active layers demonstrated great promise for the development of efficient semi-transparent organic solar cells with the potential for future applications, including but not limited to self-powered greenhouses and powered windows. Researchers seek alternative solutions to trade-off between the power conversion efficiency (PCE) and average visible transmittance (AVT) of ST-OSCs, with photoactive materials being the key parameters that govern both (PCE) and (AVT), as well as device stability. Several new organic materials, including polymers and small molecules, were synthesized and used in conjunction with a variety of techniques to achieve semi-transparent conditions. In this review paper, we look at the working principle and key parameters of semi-transparent organic solar cells, as well as the methods that have been used to improve the performance and stability of ternary-based semi-transparent organic solar cells. The main approaches were concluded to be spectral enhancement and increments in the transparency of the active layer through band gap tuning, utilizing novel organic semi-conductors, optical engineering, and the design architecture of the active layers. [ABSTRACT FROM AUTHOR]

Blend films of poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b']dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) in combination with 6,6‐phenyl‐C61‐butyric‐acid‐methyl‐ester (PCBM) are a model system for low bandgap organic photovoltaics. Typically, solvent additives are used to improve the power conversion efficiencies of the resulting devices but possibly also decrease the device stability. In this study, we use the binary solvent additive 1,8‐diiodooctane:diphenylether (DIO:DPE) for PTB7:PCBM blend films and study how different film drying procedures influence the physical and chemical stability of the polymer blend. The strong influence of the drying procedure on the stability against photoinduced degradation of the PTB7:PCBM films, produced with solvent additives, is shown with data from UV–visible (UV–vis), Fourier transform infrared (FTIR) and Raman spectroscopy. The addition of solvent additive molecules DIO:DPE to the PTB7:PCBM blend accelerates the degradation compared with the pristine blend. At higher annealing temperature a removal of the additives is bringing degradation back to the level of the pristine blend films, which is promising for photovoltaic applications. [ABSTRACT FROM AUTHOR]

Bulk heterojunction (BHJ) composites show improved power conversion efficiencies when optimized in terms of morphology using various film processing methods. A reduced carrier recombination loss in an optimized BHJ was characterized previously. However, the driving force that leads to this reduction was not clearly understood. In this study, we focus on the decreased carrier recombination loss and its driving force in optimized nonfullerene acceptor‐based PTB7‐Th:IEICO‐4F BHJ composites. We demonstrate that the optimized BHJ shows deactivation in the sub‐nanosecond nongeminate carrier recombination process. The driving force for this deactivation was determined to be the improved interchain hole delocalization between the polymers. An enhanced interchain hole delocalization was observed using steady‐state photoinduced absorption (PIA) spectroscopy. In particular, increased splitting between the polaron PIA bands was noted. Moreover, improved interchain hole delocalization was observed for other state‐of‐the‐art BHJ materials, including D18:Y6 with optimized morphologies. [ABSTRACT FROM AUTHOR]

Theoretical simulation of film morphology with bulk heterojunction (BHJ) has become a technological breakthrough point for material and performance development in recent years. Stemming from the precision of calculation and the boom of materials, the unified process for predicting the relevant properties of BHJ through monomers needs to be further updated. This study analyzed the sensibilities of environmental changes (monomers, the acceptors of D/A and A/A in morphology) on structures and properties from fullerene to non‐fullerene materials. The results showed that it is inaccurate to predict morphology only by optimizing the monomer through employing a unified process. Due to material specificity, excessive environmental sensitivity could lead to prediction errors. In different environments, the properties of C60 with rigid structure vary greatly. The stability of fused ring electron acceptors (FREAs) is determined by the type and number of bridge bonds (single and ethylenic bonds) in main backbones, where a small number and strong conjugation are favorable. As a result, flexible ITIC is insensitive to the environment, which could be performed using a unified process. This may be the main reason for their excellent properties. This work puts forward higher requirements for the accuracy of a theoretical calculation process, and also provides an updated theoretical account for an accurate design of bulk heterojunction. [ABSTRACT FROM AUTHOR]

Organic semiconductor-based photoelectrodes are gaining significant attention in photoelectrochemical (PEC) value-added chemical production systems, which are promising architectures for solar energy harvesting. Organic semiconductors consisting of conjugated carbon–carbon bonds provide several advantages for PEC cells, including improved charge transfer, tunable band positions and band gaps, low cost, and facile fabrication using organic solvents. This review gives an overview of the recent advances in emerging single organic semiconductor-based photoelectrodes for PEC water splitting and the various strategies for enhancing their performance and stability. It highlights the importance of photoelectrodes based on donor–acceptor bulk heterojunction (BHJ) systems for fabricating efficient organic semiconductor-based solar energy-harvesting devices. Furthermore, it evaluates the recent progress in BHJ organic base photoelectrodes for producing highly efficient PEC value-added chemicals, such as hydrogen and hydrogen peroxide. Finally, this review highlights the potential of organic-based photoelectrodes for bias-free solar-to-chemical production, which is the ultimate goal of PEC systems and a step toward achieving reliable commercial technology. [ABSTRACT FROM AUTHOR]

Photovoltaic structures of the bulk heterojunction type were fabricated, in which derivatives of N,N-diethylamine-3-Methyl-1-Phenyl-1H-pyrazolo[3,4-b]quinoxalines were used as the active layer. The compounds differed in the position of the electron-donating substituent in the carbocyclic ring. Four isomers were subjected to UV-Vis spectrophotometric measurements in solvents of different polarities. The absorption characteristics were experimentally determined for the tested derivatives. The values of HOMO-LUMO levels were determined by means of quantum chemical calculations using the HyperChem software. The current–voltage and dispersion characteristics of the produced OPV were determined. The spectral characteristics of the refractive indices and extinction coefficients of the active layers were determined using the spectroscopic ellipsometry method. These results were used in the analysis and optimization of photovoltaic structures. It was shown that the location of the N,N-diethylamine substituent affects the photophysical properties of the structure and the photovoltaic properties. The optimization of the OPV_2 photovoltaic structure using the coherent model and the 2 × 2 matrix method can be successfully used in modeling optical multilayer structures, including photovoltaic structures. [ABSTRACT FROM AUTHOR]

Organic solar cells have obtained a prodigious amount of attention in photovoltaic research due to their unique features of light weight, low cost, eco-friendliness, and semitransparency. A rising trend in this field is the development of all-small-molecules organic solar cells (ASM-OSCs) due to their merits of excellent batch-to-batch reproducibility, well-defined structures, and simple purification. Among the numerous organic photovoltaic (OPV) materials, benzodithiophene (BDT)-based small molecules have come to the fore in achieving outstanding power conversion efficiency (PCE) and breaking the 17% efficiency barrier in single-junction OPV devices, indicating the significant potential of this class of materials in commercial photovoltaic applications. This review specially focuses on up-to-date information about improvements in BDT-based ASM-OSCs since 2011 and provides an outlook on the most significant challenges that remain in the field. We believe there will be more exciting BDT-based photovoltaic materials and devices developed in the near future. [ABSTRACT FROM AUTHOR]

Abstract Bulk heterojunction (BHJ) composites show improved power conversion efficiencies when optimized in terms of morphology using various film processing methods. A reduced carrier recombination loss in an optimized BHJ was characterized previously. However, the driving force that leads to this reduction was not clearly understood. In this study, we focus on the decreased carrier recombination loss and its driving force in optimized nonfullerene acceptor‐based PTB7‐Th:IEICO‐4F BHJ composites. We demonstrate that the optimized BHJ shows deactivation in the sub‐nanosecond nongeminate carrier recombination process. The driving force for this deactivation was determined to be the improved interchain hole delocalization between the polymers. An enhanced interchain hole delocalization was observed using steady‐state photoinduced absorption (PIA) spectroscopy. In particular, increased splitting between the polaron PIA bands was noted. Moreover, improved interchain hole delocalization was observed for other state‐of‐the‐art BHJ materials, including D18:Y6 with optimized morphologies.

Fluorinated multi-walled carbon nanotubes are implemented as the third component of the active layer of organic solar cells. The addition of approximately 1% weight fraction of these nanotubes into PCDTBT/PC60BM polymer/fullerene active layer leads to a noticeable increase in the main photovoltaic parameters of the solar cells, including their stability. Presumably, the origins of this influence are optimizing the donor/acceptor composite morphology and reinforcing its structure with fluorinated multi-walled carbon nanotubes. This hypothesis is supported by the dramatic influence of the fluorinated multi-walled carbon nanotube additive on the kinetics of the decay of the EPR signal of light-induced charges in the PCDTBT/PC60BM composite.

This report demonstrates high-performance infrared phototransistors that use a broad-band absorbing organic bulk heterojunction (BHJ) layer responsive from the visible to the shortwave infrared, from 500 to 1400 nm. The device structure is based on a bilayer transistor channel that decouples charge photogeneration and transport, enabling independent optimization of each process. The organic BHJ layer is improved by incorporating camphor, a highly polarizable additive that increases carrier lifetime. An indium zinc oxide transport layer with high electron mobility is employed for rapid charge transport. As a result, the phototransistors achieve a dynamic range of 127 dB and reach a specific detectivity of 5 × 1012 Jones under a low power illumination of 20 nW/cm2, outperforming commercial germanium photodiodes in the spectral range below 1300 nm. The photodetector metrics are measured with respect to the applied voltage, incident light power, and temporal bandwidth, demonstrating operation at a video-frame rate of 50 Hz. In particular, the frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions.

The narrow bandgap of the low-energy near-infrared (NIR) polymer would lead to overlap between adjacent energy levels, which is a major barrier to the preparation of Vis-NIR polymer bulk heterojunction (BHJ) photodetectors with small responsivity and photocurrent. In this study, a high-performance lateral inorganic-organic hybrid photodetector was constructed to eliminate this barrier by combining GaN nanowires (GaN-NWs) with PDPP3T:PC61BM-based BHJ. In stage one, high-quality GaN-NWs were synthesized by the catalyst-free CVD method. The mechanism for controlling GaN-NWs morphology by adjusting the NH3 flow rate was revealed. In stage two, the GaN-NWs with large electron mobility were used to accelerate the transfer of photogenerated carriers in the BHJ layer. Finally, compared with the BHJ device, the BHJ/GaN device demonstrated obvious improvements in responsivity and photocurrent at the wavelength between 400 and 1000 nm. The responsivity and photocurrent increased over 20-fold at the NIR band of 800–900 nm. Besides, owing to the energy level gradient effect, the BHJ/GaN device has a response speed of 7.8/

A series of phenothiazine-C60/70 dyads containing fulleropyrrolidine tethered to C-3 position (C60-PTZ and C70-PTZ) or to the heteroatom N-position via either phenyl (C60-Ph–PTZ and C70-Ph-PTZ) or phenoxyethyl linkers (C60-PhOEt-PTZ and C70-PhOEt-PTZ) of the phenothiazine were synthesized and light-induced electron transfer events were explored. Optimized studies suggested that the highest molecular orbital (HOMO) resides on donor phenothiazine moiety while lowest molecular orbital (LUMO) on the acceptor fulleropyrrolidine moiety of the dyads. Optical and electrochemical properties suggested no electronic communication between the donor and acceptor moieties in the ground state. However, steady-state emission studies in solvents of varied polarity, involving selective excitation of C60/C70, disclosed that the emission intensity of C60/C70 was quenched in the dyads in the increasing order, C60/70-PTZ > C60/70-Ph-PTZ > C60/70-PhOEt-PTZ as a consequence of the donor–acceptor distance resulted due to spacer lengths. Also, the emission quenching is more pronounced in polar solvents such as DMF compared to a non-polar solvent, toluene. With the support of parallel electrochemical studies, the emission quenching is attributed to intramolecular photo-induced electron transfer occurring from PTZ to (C60/C70)* generating a radical ion pair, PTZ+⋅–C60−⋅/PTZ+⋅–C70−⋅. Finally, bulk heterojunction (BHJ) solar cells devices inverted fashion prepared by employing the dyads as acceptors, and PTB7 as donor, suggested that the devices prepared from C70 derivatives i.e., PTB7:C70-PTZ and PTB7:C70-PhOEt-PTZ exhibited better power conversion efficiency of 2.66% and 2.15%, respectively over C60 derivatives i.e., PTB7:C60-PTZ and PTB7:C60-PhOEt-PTZ with the efficiencies of 1.80 and 1.72%, respectively. AFM studies revealed that the poor performance of PTB7:C60-PTZ- and PTB7:C60-PhOEt-PTZ-based devices can be ascribed to the lower solubility of the dyads in 1,2-DCB solvent leading to rough morphology. [ABSTRACT FROM AUTHOR]

To modulate the miscibility between donor and acceptor materials both possessing fully non‐fused ring structures, a series of electron acceptors (A4T‐16, A4T‐31 and A4T‐32) with different polar functional substituents were synthesized and investigated. The three acceptors show good planarity, high conformational stability, complementary absorption and energy levels with the non‐fused polymer donor (PTVT‐BT). Among them, A4T‐32 possesses the strongest polar functional group and shows the highest surface energy, which facilitates morphological modulation in the bulk heterojunction (BHJ) blend. Benefiting from the proper morphology control method, an impressive power conversion efficiency (PCE) of approaching 16.0 % and a superior fill factor over 0.795 are achieved in the PTVT‐BT : A4T‐32‐based organic photovoltaic cells with superior photoactive materials price advantage, which represent the highest value for the cells based on the non‐fused blend films. Notably, this cell maintains ≈84 % of its initial PCE after nearly 2000 h under the continuous simulated 1‐sun‐illumination. In addition, the flexible PTVT‐BT : A4T‐32‐based cells were fabricated and delivered a decent PCE of 14.6 %. This work provides an effective molecular design strategy for the non‐fused non‐fullerene acceptors (NFAs) from the aspect of bulk morphology control in fully non‐fused BHJ layers, which is crucial for their practical applications. [ABSTRACT FROM AUTHOR]

The fluorination strategy is one of the most efficient and popular molecular modification methods to develop new materials for organic photovoltaic (OPV) cells. For OPV materials, it is a broad agreement that fluorination can reduce the energy level and change the morphology of active layers. To explore the effect of fluorination on small molecule acceptors, we selected two non-fullerene acceptors (NFA) based bulk heterojunction (BHJ) films, involving PM6:Y6 and PM6:Y5 as model systems. The electron mobilities of the PM6:Y5 and PM6:Y6 BHJ films are 5.76 × 10−7 cm2V−1s−1 and 5.02 × 10−5 cm2V−1s−1 from the space-charge-limited current (SCLC) measurements. Through molecular dynamics (MD) simulation, it is observed that halogen bonds can be formed between Y6 dimers, which can provide external channels for electron carrier transfer. Meanwhile, the "A-to-A" type J-aggregates are more likely to be generated between Y6 molecules, and the π–π stacking can be also enhanced, thus increasing the charge transfer rate and electron mobility between Y6 molecules. [ABSTRACT FROM AUTHOR]

The properties of organic heterostructures with mixed layers made of arylenevinylene-based polymer donor and non-fullerene perylene diimide acceptor, deposited using Matrix Assisted Pulsed Laser Evaporation on flat Al and nano-patterned Al electrodes, were investigated. The Al layer electrode deposited on the 2D array of cylindrical nanostructures with a periodicity of 1.1 µm, developed in a polymeric layer using UV-Nanoimprint Lithography, is characterized by an inflorescence-like morphology. The effect of the nanostructuring on the optical and electrical properties was studied by comparison with those of the heterostructures based on a mixed layer with fullerene derivative acceptor. The low roughness of the mixed layer deposited on flat Al was associated with high reflectance. The nano-patterning, which was preserved in the mixed layer, determining the light trapping by multiple scattering, correlated with the high roughness and led to lower reflectance. A decrease was also revealed in photoluminescence emission both at UV and Vis excitation of the mixed layer, with the non-fullerene acceptor deposited on nano-patterned Al. An injector contact behavior was highlighted for all Al/mixed layer/ITO heterostructures by I-V characteristics in dark. The current increased, independently of acceptor (fullerene or non-fullerene), in the heterostructures with nano-patterned Al electrodes for shorter conjugation length polymer donors. [ABSTRACT FROM AUTHOR]

[Display omitted] The communalization of all-polymer solar cells depends on the cost of active layer materials. We have introduced a framework to find the easily synthesizable polymers. Breaking Retrosynthetically Interesting Chemical Substructures (BRICS) method is used to generate a large database of polymers and synthetic accessibility of generated polymers is predicted. The generated database is visualized using various methods. Energy levels of polymers are also predicted using pretrained machine learning models. Polymers are screened on the basis of predicted properties. Library of polymers are displayed using the T -distributed Stochastic Neighbor Embedding (t -SNE) visualization. Structure Activity Landscape Index (SALI) visualization is also used. A significant change is observed in synthetic accessibility score on structural changes. The histagradient boosting regressor is used to predict the energy levels of polymers that energy levels play significant role in the selection of materials for organic photovoltaic cells. Synthetic accessibility of polymers is analyzed and a significant number of polymers are easy to synthesize. Thirty polymers are selected through screening process that are potential candidates for organic photovoltaic cells. [ABSTRACT FROM AUTHOR]

Organic materials are known for their variety of molecules. Methods to predict the parameters of organic photovoltaic (OPV) cells are required to avoid the time- and resource-consuming processes of manufacturing and testing OPVs. Usually, the open-circuit voltage (Uoc) is estimated as the difference between the ionization energy level of the electron donor molecule (Id) and the electron affinity level of the electron acceptor molecule (EAa). Various measurement methods are used to determine the energy level values of pure materials, which, when combined with energy level shifts due to the donor:acceptor interactions, make these estimations less precise. In this work, photoconductivity measurements were applied to the donor:acceptor films. Near threshold energy, the electron can be directly transferred from the donor to the acceptor molecule. The obtained charge transfer energy (ECT) shows the difference between Id and EAa in the film. This difference was compared to the Uoc value of an OPV made of the same donor:acceptor combination. We show that this approach provides less scattered results and a higher correlation coefficient compared to the Uoc estimation using energy level values.

Current-voltage characteristics of an organic solar cells can be tuned by tailoring the active layer material’s polymer chain ordering which in turn decides the PV performance. The suppression of exciton recombination, improved charge carrier separation, large carrier diffusion length can be achieved by improving the packing density of the π-π stacking, polymer chain length and chain ordering. The high packing density π-π stacking can be formed through enhancing the percentage of crystallinity of the semiconducting polymer layer. This can be achieved by optimizing the processing parameters. This work gives some insights on the spinning time of active layer (P3HT:PC61BM) on the structural, optical and solar cell performance. P3HT:PC61BM crystalline properties were studied through grazing incidence X-ray diffraction (GI-XRD). Optical absorption of the active layer was studied by the UV–visible spectrometer. The trap density of states of the solar cells processed at various active layer spinning condition is evaluated. From the obtained result it is noted that device fabricated with longer spinning time showed higher power conversion efficiency over shorter spinning duration. These changes in the device performance could be due to solvent evaporation kinetics, chain alignment in the polymer thin film. Further, the mechanism of trap states formation based on the active layer processing condition is explained.

Infrared organic photodetector materials are investigated using transient absorption spectroscopy, demonstrating that ultrafast charge generation assisted by polymer aggregation is essential to compensate for the energy gap law, which dictates that excited state lifetimes decrease as the band gap narrows. Short sub-picosecond singlet exciton lifetimes are measured in a structurally related series of infrared-absorbing copolymers that consist of alternating cyclopentadithiophene electron-rich “push” units and strong electron-deficient “pull” units, including benzothiadiazole, benzoselenadiazole, pyridalselenadiazole, or thiadiazoloquinoxaline. While the ultrafast lifetimes of excitons localized on individual polymer chains suggest that charge carrier generation will be inefficient, high detectivity for polymer:PC71BM infrared photodetectors is measured in the 0.6 < λ < 1.5 µm range. The photophysical processes leading to charge generation are investigated by performing a global analysis on transient absorption data of blended polymer:PC71BM films. In these blends, charge carriers form primarily at polymer aggregate sites on the ultrafast time scale (within our instrument response), leaving quickly decaying single-chain excitons unquenched. The results have important implications for the further development of organic infrared optoelectronic devices, where targeting processes such as excited state delocalization over aggregates may be necessary to mitigate losses to ultrafast exciton decay as materials with even lower band gaps are developed.