Device Fabrication Conditions Research Articles

One-volt oxide based complementary circuit

In low-power electronics, there is a substantial demand for high-performance p-type oxide thin-film transistors (TFTs) that are capable of efficient operation at low voltages. In this study, we employ anodization to form an aluminum oxide gate dielectric layer, enabling the fabrication of p-type tin oxide (SnO) TFTs that effectively operate at a low voltage of 1 V. Under optimal device fabrication conditions, the SnO TFT demonstrates an on/off current ratio exceeding 103 and a saturation mobility of 1.94 cm2 V−1 s−1 at 1 V operation. The optimal SnO TFT fabrication conditions are subsequently used to fabricate a complementary inverter, comprising a SnO TFT and an n-type indium gallium zinc oxide TFT, achieving a gain of up to 38 at a 1 V supply voltage. Notably, the inverter’s switching point voltage is finely tuned to the ideal value, precisely half of the supply voltage. This oxide-based complementary inverter showcases promising potential in low-power electronics.

Concretized structural evolution supported assembly-controlled film-forming kinetics in slot-die coated organic photovoltaics

Bulk-heterojunction structured small-area organic solar cells are approaching 20% power conversion efficiency, but the blurred film-forming kinetics in the fabrication of large-area devices causes significant PCE loss and restrains the potential of commercialization. Such blurring came from insufficient knowledge of structural evolution during the film-forming process. Here, we concretize the evolution process with structures detailed to the submolecular level by comprehensive investigations of in-situ UV-vis spectroscopy, Atomic Force Microscope, Grazing Incident Wide Angle X-ray Scattering, and molecular dynamic simulation. With such hierarchical structural knowledge, assembly-controlled film-forming kinetics is proposed to explain the whole picture. Such assembly is determined by molecule configuration and can be tuned via external conditions. Understanding this kinetics will contribute to screening large-area device fabrication conditions, and the detailed structural knowledge could inspire the future design of novel photovoltaic materials that are intrinsically excellent in large-area device fabrications.

Machine Learning Assisted Analysis, Prediction, and Fabrication of High‐Efficiency CZTSSe Thin Film Solar Cells

AbstractThe Earth‐abundant element‐based Cu2ZnSn(S,Se)4 (CZTSSe) absorber is considered as a promising material for thin‐film solar cells (TFSCs). The current record power conversion efficiency (PCE) of CZTSSe TFSCs is ≈13%, and it's still lower than CdTe and CIGS‐based TFSCs. A further breakthrough in its PCE mainly relies on deep insights into the various device fabrication conditions; accordingly, the experimental–oriented machine learning (ML) approach can be an effective way to discover key governing factors in improving PCE. The present work aims to identify the key governing factors throughout the device fabrication processes and apply them to break the saturated PCE for CZTSSe TFSCs. For realization, over 25,000 data points were broadly collected by fabricating more than 1300 CZTSSe TFSC devices and analyzed them using various ML techniques. Through extensive ML analysis, the i‐ZnO thickness is found to be the first, while Zn/Sn compositional ratio and sulfo‐selenization temperature are other key governing factors under thin or thick i‐ZnO thickness to achieve over 11% PCE. Based on these key governing factors, the applied random forest ML prediction model for PCE showed Adj. R2 = >0.96. Finally, the best‐predicted ML conditions considered for experimental validation showed well‐matched experimental outcomes with different ML models.

Miscibility Regulation and Thermal Annealing Induced Hierarchical Morphology Enables High‐Efficiency All‐Small‐Molecule Organic Solar Cells Over 17%

AbstractAchieving an ideal morphology to realize efficient charge generation and transport is an imperative avenue to improve the photovoltaic performance of all small‐molecule organic solar cells (SM‐OSCs). Here, ternary SM‐OSCs are fabricated based on a new small molecule donor, SM‐mB, and an alloyed blend acceptor of Y6 and its derivative, L8‐BO, and desirable hierarchical morphology with appropriate nanoscale phase separation is successfully realized through adjusting the thermal annealing treatment conditions and compositions of mixed acceptors in the active layer. Then the ternary SM‐OSCs achieve an excellent PCE of 17.06 %, which is one of the best results for the SM‐OSCs so far. The desirable morphology can be ascribed to the optimization of the miscibility‐driven donor and acceptor blend morphology that takes full advantage of the individual advantages of both acceptors, which facilitate efficient charge generation and extraction with more balanced charge carrier mobilities. More importantly, the photovoltaic performance of the ternary SM‐OSCs possesses a high tolerance to the device fabrication conditions, including thermal annealing treatment, and is insensitive to film thickness, which is beneficial for large‐area manufacture and future practical applications.

Molecular Engineering of Enamine‐Based Hole‐Transporting Materials for High‐Performing Perovskite Solar Cells: Influence of the Central Heteroatom

Stabilizing the high‐performing perovskite solar cells (PSCs) with low‐cost and simply affordable hole‐transporting materials (HTMs) has been identified as an ongoing ambitious challenge. Herein, a series of enamine‐based HTMs having different central heteroatoms (C, N, O, and S) and a number of enamine branches is designed and synthesized. The impact of varied central heteroatom cores is investigated in‐depth including thermal, photophysical, and photovoltaic properties. Importantly, molecularly engineered HTMs are obtained by a single condensation reaction without the need for expensive catalysts, inert reaction conditions, or tedious product purification. PSCs with a power conversion efficiency (PCE) of over 20% can be realized with the triphenylamine core HTM (V1435), a result comparable with spiro‐OMeTAD. HTMs based on tetraphenylmethane (V1431) and diphenyl sulfide (V1434) cores give a slightly lower performance under similar device fabrication conditions. This work demonstrates how rational molecular engineering of a simple condensation approach can produce HTMs for high‐performing PSCs without sacrificing the PCE.

18.55% Efficiency Polymer Solar Cells Based on a Small Molecule Acceptor with Alkylthienyl Outer Side Chains and a Low-Cost Polymer Donor PTQ10

18.55% Efficiency Polymer Solar Cells Based on a Small Molecule Acceptor with Alkylthienyl Outer Side Chains and a Low-Cost Polymer Donor PTQ10

Synthesis of Group II-VI Semiconductor Nanocrystals via Phosphine Free Method and Their Application in Solution Processed Photovoltaic Devices.

Solution-processed CdTe semiconductor nanocrystals (NCs) have exhibited astonishing potential in fabricating low-cost, low materials consumption and highly efficient photovoltaic devices. However, most of the conventional CdTe NCs reported are synthesized through high temperature microemulsion method with high toxic trioctylphosphine tellurite (TOP-Te) or tributylphosphine tellurite (TBP-Te) as tellurium precursor. These hazardous substances used in the fabrication process of CdTe NCs are drawing them back from further application. Herein, we report a phosphine-free method for synthesizing group II-VI semiconductor NCs with alkyl amine and alkyl acid as ligands. Based on various characterizations like UV-vis absorption (UV), transmission electron microscope (TEM), and X-ray diffraction (XRD), among others, the properties of the as-synthesized CdS, CdSe, and CdTe NCs are determined. High-quality semiconductor NCs with easily controlled size and morphology could be fabricated through this phosphine-free method. To further investigate its potential to industrial application, NCs solar cells with device configuration of ITO/ZnO/CdSe/CdTe/Au and ITO/ZnO/CdS/CdTe/Au are fabricated based on NCs synthesized by this method. By optimizing the device fabrication conditions, the champion device exhibited power conversion efficiency (PCE) of 2.28%. This research paves the way for industrial production of low-cost and environmentally friendly NCs photovoltaic devices.

Molecular orientation, anisotropic electron transport and photovoltaic properties of ladder-type heteroheptacene-based semiconductors

• Alkyl chains are used to control the molecular orientation and charge transport. • The size of alkyl chains on the nitrogen atoms directs the backbone orientation. • A record PCE of 15.63% among A-D-A-type acceptors with chlorinated end groups. • Edge-on orientation leads to a high transistor mobility of 3.95 × 10 −2 cm 2 V −1 s −1 . Control over the molecular orientation of organic semiconductors with respect to the substrate plays a critical role in determining the performance of organic electronic devices. In this work, three ladder-type heteroheptacene-based small molecules with branched or unbranched side chains flanked in different positions of their conjugated backbone (M11, M12, and M13), were designed and synthesized to investigate the effect of side-chains on the crystallinity, molecular orientation, and optoelectronic properties of the organic semiconductors. When linear n-dodecyl side-chains are attached to the nitrogen atoms of the heteroheptacene core, the resulting molecule (M11) exhibits high crystallinity and edge-on molecular orientation, thus leading to excellent horizontal charge transport with a field-effect transistor (FET) mobility of 3.95 × 10 −2 cm 2 V −1 s −1 . Replacing the linear n-dodecyl chains on the nitrogen atoms with the branched 2-butyloctyl chains leads to the organic semiconductors (M12 and M13) with the face-on dominated molecular orientation thereby leading to two orders of magnitude enhancement in the vertical charge transport in comparison with M11. Consequently, M12 and M13 show much higher power conversion efficiencies (PCEs) of 11.55% and 13.14%, respectively, compared to M11 which exhibits a PCE of 2.26% under the same device fabrication conditions. Optimization on the M13-based solar cells yields a further improved PCE of 15.63% which is among the highest values for the A-D-A type nonfullerene acceptors. The results reported in this work highlight that modulating the molecular orientation of organic semiconductors is a highly effective molecular design strategy to boost the performance of optoelectronic devices, thus also providing new insights into the molecular design guidelines for the next generation of high-performance semiconductors for the FET and photovoltaic applications.

Observation of dopant-dependent efficiency in chemically doped graphene/silicon solar cells and prospects for MoOx to overcome the stability and efficiency limits

Heterointegration of graphene with silicon has attracted growing interest, because the resulting unique heterojunction allows for efficient collection of light generated electron–hole pairs. This study aims to understand the role of device fabrication conditions and electronic properties of chemically doped graphene on the efficiency variations and stability of graphene/silicon solar cells. We observed significant variations in the efficiency between the devices doped with metal chloride and organic molecules. A strong degradation in the hole carrier mobility by the formation of metal particles/clusters, which could act like charge puddles, accounts for the limited efficiency in the former. Molecular doping, on the other hand, offered good doping homogeneity and no mobility degradation, leading to solar cells with efficiency as high as 9.2%. Our results demonstrate that the droop in efficiency over time observed in the chemically doped devices is due to oxidation limited charge carrier separation rather than doping reversal. The prospects of molybdenum oxide (MoOx) as a multifunctional layer in improving the device stability and efficiency are also discussed based on preliminary experimental findings.

Non-plasmonic improvement in photoconductive THz emitters using nano- and micro-structured electrodes.

We investigate here terahertz enhancement effects arising from micrometer and nanometer structured electrode features of photoconductive terahertz emitters. Nanostructured electrode based emitters utilizing the palsmonic effect are currently one of the hottest topics in the research field. We demonstrate here that even in the absence of any plasmonic resonance with the pump pulse, such structures can improve the antenna effect by enhancing the local d.c. electric field near the structure edges. Utilizing this effect in Hilbert-fractal and grating-like designs, enhancement of the THz field of up to a factor of ∼ 2 is observed. We conclude that the cause of this THz emission enhancement in our emitters is different from the earlier reported plasmonic-electrode effect in a similar grating-like structure. In our structure, the proximity of photoexcited carriers to the electrodes and local bias field enhancement close to the metallization cause the enhanced efficiency. Due to the nature of this effect, the THz emission efficiency is almost independent of the pump laser polarization. Compared to the plasmonic effect, these effects work under relaxed device fabrication and operating conditions.

A Robust Metal Oxide Thin Film with Cryogenic Saturation Magnetization Exceeding 2 Tesla

Summary High saturation magnetization, hysteresis-less long linear response range, and resistance to device fabrication conditions are figures of merit for magnetic materials. Despite advances in materials research, many high-saturating micro- and nanomagnetic materials are hysteresis-prone, have short linear ranges, and are sensitive to oxidation, resulting in device inefficiencies in high-frequency electronics and unpredictable responses in magnetic sensing applications. Holmium oxide is a promising material because of its high magnetic susceptibility, but synthetic options are limited, with low-temperature magnetism incompletely characterized. Here, we present physical vapor deposition synthesis and material characterization of polycrystalline holmium oxide thin films. The product has saturation magnetization exceeding 2 Tesla, linear range (μ0H) also exceeding 2 Tesla, zero magnetic remanence and coercivity, and resistance to harsh processing conditions including oxygen plasma and concentrated hydrofluoric acid etching, making these thin films ideal for fabricating next-generation nanoscale magnetic devices in advanced scientific and engineering applications.

Dopant-Free Crossconjugated Hole-Transporting Polymers for Highly Efficient Perovskite Solar Cells.

Currently, there are only very few dopant‐free polymer hole‐transporting materials (HTMs) that can enable perovskite solar cells (PVSCs) to demonstrate a high power conversion efficiency (PCE) of greater than 20%. To address this need, a simple and efficient way is developed to synthesize novel crossconjugated polymers as high performance dopant‐free HTMs to endow PVSCs with a high PCE of 21.3%, which is among the highest values reported for single‐junction inverted PVSCs. More importantly, rational understanding of the reasons why two isomeric polymer HTMs (PPE1 and PPE2) with almost identical photophysical properties, hole‐transporting ability, and surface wettability deliver so distinctly different device performance under similar device fabrication conditions is manifested. PPE2 is found to improve the quality of perovskite films cast on top with larger grain sizes and more oriented crystallization. These results help unveil the new HTM design rules to influence the perovskite growth/crystallization for improving the performance of inverted PVSCs.

Solution-processed method for high-performance Cu2ZnSn(S,Se)4 thin film solar cells and its characteristics

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) has attracted much attention as an ideal absorber material for thin film solar cells. Solution deposition methods provide a crucial approach for lowering the fabricating price of CZTSSe based photovoltaic devices. Here, a low-cost and robust ethanol/thioglycolic acid/1-butylamine ternary solutions method was developed to fabricate the CZTSSe solar cells. Characterization was performed using XRD, Raman, and C–V, which showed that the material fabricated by this method expressed high-phase purity, suitable carrier concentration, and large depletion width, and those features are vital to high efficiency photovoltaic devices. Hence, based on this high quality CZTSSe absorbed layer, photovoltaic device with a power conversion efficiency (PCE) as high as 9.71% was achieved. The PCE can be further enhanced through passivating with alkali metal and optimizing the device fabrication conditions, making this method much promising for lowering the manufacturing cost of kesterite solar cells. Additionally, this approach is full of application prospect for other burgeoning photovoltaic absorber materials which could dramatically reduce the cost of solar electricity.

Comparison of processing-induced deformations of InP bonded to Si determined by e-beam metrology: Direct vs. adhesive bonding

In this paper, we employ an electron beam writer as metrology tool to investigate distortion of an exposed pattern of alignment marks in heterogeneously bonded InP on silicon. After experimental study of three different bonding and processing configurations which represent typical on-chip photonic device fabrication conditions, the smallest degree of linearly-corrected distortion errors is obtained for the directly bonded wafer, with the alignment marks both formed and measured on the same InP layer side after bonding (equivalent to single-sided processing of the bonded layer). Under these conditions, multilayer exposure alignment accuracy is limited by the InP layer deformation after the initial pattern exposure mainly due to the mechanical wafer clamping in the e-beam cassette. Bonding-induced InP layer deformations dominate in cases of direct and BCB bonding when the alignment marks are formed on one InP wafer side, and measured after bonding and substrate removal from another (equivalent to double-sided processing of the bonded layer). The findings of this paper provide valuable insight into the origin of the multilayer exposure misalignment errors for the bonded III-V on Si wafers, and identify important measures that need to be taken to optimize the fabrication procedures for demonstration of efficient and high-performance on-chip photonic integrated devices.

Over 10% Efficient CuIn(S,Se)2 Solar Cells Fabricated From Environmentally Benign Solution in Air

A safe and environmentally benign solvent is a requisite for mass production of thin film solar cells via solution methods. Here, a highly industry suitable solvent N‐methyl‐pyrrolidone (NMP) is used for the first time to make a precursor solution with simple compounds of CuCl, InCl3·4H2O and thiourea and fabricate CuIn(S,Se)2 (CISSe) solar cells. A power conversion efficiency of 10.23% has been achieved from the NMP‐based solution when the precursor film was processed in air, which is only 8.55% for film processed in glove box. Characterizations using XRD, Raman, SEM, EDX, and FTIR show air annealing favors decomposition of organic species in the precursor film, which results in high quality absorber materials. Further improvement in device efficiency can be expected by gallium alloying and optimization of device fabrication conditions. The results demonstrate highly efficient thin film solar cells can be fabricated from an industry suitable NMP precursor solution in air, which is promising for simplifying film processing and reducing manufacture cost.

Effect of Water, Oxygen, and Air Exposure on CH3NH3PbI3–xClx Perovskite Surface Electronic Properties

AbstractThe stability of hybrid perovskite materials for solar cells and high surface property reproducibility are important topics of present research. To understand the impact of water, oxygen, and air exposure, as experienced during typical device fabrication and operation conditions, on the surface electronic properties of solution‐processed CH3NH3PbI3–xClx perovskite thin films, and subsequently formed interfaces to other materials, a comprehensive photoelectron spectroscopy study is performed. It is shown that pure oxygen exposure reduces the typically observed pronounced n‐type surface character, while pure water exposure increases it. Very low water partial pressure, e.g., as encountered in inert‐gas glove boxes and in high vacuum of 10−6 mbar, reduces the perovskite work function due to water physisorption, which is fully reversible upon mild annealing (room temperature to 50 °C) in ultrahigh vacuum. Upon exposure to ambient air, the effect of oxygen prevails over that of water, and the perovskite become less n‐type as seen by a 0.6 eV Fermi level shift toward midgap. The results help in understanding variations of the surface electronic properties reported for perovskites, which in turn impact the energy level alignment at heterojunctions in devices. For future studies, the crucial importance of stringent environment control is stressed upon.

Comparison of Three n-Type Copolymers Based on Benzodithiophene and Naphthalene Diimide/Perylene Diimide/Fused Perylene Diimides for All-Polymer Solar Cells Application.

All-polymer solar cells have gained large attention in recent years because of their tunable energy levels and absorption spectra for both polymeric donor and acceptor. Comparing with the numerous polymeric donors, the development of polymeric acceptors was relatively slow. Rylene diimide-based polymers are regarded as the most promising n-type polymers, which were widely investigated in the past decade, and some novel rylene diimide structures are constantly designed. In this work, three n-type polymers with a donor/acceptor (D/A) alternative backbone structure, named PNDI-BDT, PPDI-BDT, and PFPDI-BDT, were synthesized. In these polymers, naphthalene diimide (NDI), perylene diimide (PDI), and recently developed fused perylene diimide (FPDI) were utilized as electron-withdrawing segment, respectively, and benzodithiophene (BDT) with thiophenes as conjugated side chains was utilized as an electron-rich unit. The optical properties, electron energy levels, charge transport properties, photovoltaic performance, charge recombination loss, and surface morphology were systematically investigated. After optimizing the device fabrication conditions, PNDI-BDT-, PPDI-BDT-, and PFPDI-BDT-based photovoltaic cells realized the power conversion efficiencies of 0.88, 3.74, and 5.65%, respectively. Our results indicate that FPDI is a better electron-deficient segment in comparison with NDI and PDI, for the design of n-type photovoltaic polymers.

10.3% Efficient CuIn(S,Se)2 Solar Cells from DMF Molecular Solution with the Absorber Selenized under High Argon Pressure

Fabricating high performing chalcopyrite absorber material from environmental benign solvent is very important for large scale manufacturing production. Here, N, N‐dimethylformamide (DMF) is used as a single solvent to make CuIn(S,Se)2 (CIS) molecular precursor solution and fabricate CIS absorber material. A power conversion efficiency of 10.3% has been achieved from film selenized under 1.6 atmosphere Ar pressure which is 0% for film selenized under 1 atmosphere pressure. Characterizations using XRD, SEM, TEM, EDX reveal a Cu‐rich absorber material consisting of loosely connected grains with vertical holes in film selenized under 1 atmosphere and a Cu‐poor compact large‐grain top layer with large hole bottom layer in film selenized under high Ar pressure. Further optimization of precursor formulation and device fabrication conditions to address the non‐perfect double layer structure is expected to further improve DMF solution processed CIS solar cell efficiency. Our results demonstrate annealing precursor film under increased atmosphere pressure is a new and promising strategy to fabricate high performing thin film solar cells, which can be applied to all solution processed chalcogenide solar cells including CIS, CIGS and CZTS.

A Comparative Study on Two RuII Complexes with Thiophene‐Based Ancillary Ligands for High‐Efficiency Dye‐Sensitized Solar Cells

Heteroleptic polypyridyl Ru complexes MMR‐1 and MMR‐2 containing 2‐(methylthio)thienyl and 2‐(4‐methoxyphenyl)thienyl units on the antennas of ancillary ligands, respectively, were designed, synthesized, and characterized as sensitizers for dye‐sensitized solar cells. The maximum absorption wavelength of MMR‐1 is more red‐shifted than that of MMR‐2, but MMR‐2 has a higher molar extinction coefficient, leading to better light harvesting. Under the same device‐fabrication conditions, the photovoltaic performances of these sensitizers were evaluated while anchored on mesoporous TiO2 and compared to that of the benchmark N719. Both MMR‐1 and MMR‐2 exhibited comparable or even higher solar‐to‐electric conversion efficiencies η with respect to N719 when employed as photosensitizers in DSSCs. Compared to MMR‐1, MMR‐2 exhibited better overall conversion efficiency, which was attributed to the electron‐donating effect of the 4‐methoxyphenyl group and the better absorptivity by harvesting higher‐energy photons. Complex MMR‐2 also showed higher open‐circuit voltage VOC than MMR‐1, which is likely due to the extension of the antenna of the ancillary ligand by inserting a phenyl group, which leads to less dye aggregation. The photovoltaic performance of MMR‐2 was better, with a short‐circuit photocurrent density of 16.76 mA cm–2, a VOC of 0.673 V, a fill factor of 73.5 %, and an η value of 8.29 % with the addition of 0.5 m 4‐tert‐butylpyridine (TBP) compared to 8.18 % for N719.

From Nano- to Micrometer Scale: The Role of Antisolvent Treatment on High Performance Perovskite Solar Cells

To date, antisolvent treatment has become one of the most important means to fabricate high efficiency perovskite solar cells (PSCs); however, the few reported antisolvents have not been analyzed on a uniform platform, and there is hitherto no clear reasoning in the choice of antisolvents toward high performance PSCs. Here, we study the role of the antisolvents in the nucleation kinetics of perovskite solutions and their residual influence on perovskite crystal growth, film formation, and device performance. Through X-ray diffraction analysis on the complicated double mixed perovskite, we qualitatively evaluate the impact of thermal annealing and antisolvent treatment (A.S.T.) on the phase composition and microstructure of the films. By using miscible antisolvents with high boiling point instead of immiscible low boiling point solvents, we obtain homogeneous and almost pinhole-free perovskite films. When using trifluorotoluene (TFT) to replace toluene and chlorobenzene as a novel antisolvent, we achieve a power conversion efficiency (PCE) of 20.3% under optimized device fabrication conditions with a composite perovskite as active layer. The conclusions from this study should assist in establishing reproducible fabrication processes and finding better antisolvent candidates for perovskite solar cells.