N-type Doping Research Articles

Suppressing Excess Lead Iodide Aggregation and Reducing N-Type Doping at Perovskite/HTL Interface for Efficient Perovskite Solar Cells.

Excess lead iodide (PbI2 ) aggregation at the charge carrier transport interface leads to energy loss and acts as unstable origins in perovskite solar cells (PSCs). Here, a strategy is reported to modulate the interfacial excess PbI2 by introducing π-conjugated small-molecule semiconductors 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC) into perovskite films through an antisolvent addition method. The coordination of TAPC to PbI units through the electron-donating triphenylamine groups and π-Pb2+ interactions allows for a compact perovskite film with reduced excess PbI2 aggregates. Besides, preferred energy level alignment is achieved due to the suppressed n-type doping effect at the hole transport layer (HTL) interfaces. As a result, the TAPC-modified PSC based on Cs0.05 (FA0.85 MA0.15 )0.95 Pb(I0.85 Br0.15 )3 triple-cation perovskite achieved an improved PCE from 18.37% to 20.68% and retained ≈90% of the initial efficiency after 30 days of aging under ambient conditions. Moreover, the TAPC-modified device based on FA0.95 MA0.05 PbI2.85 Br0.15 perovskite produced an improved efficiency of 23.15% compared to the control (21.19%). These results provide an effective strategy for improving the performance of PbI2 -rich PSCs.

Ionic Liquid–Graphene Interface: Effect of Anions on the Fermi Level

Since energy conversion and storage processes take place at the electrolyte–electrode interface, it is important to develop experimental and theoretical procedures to understand the interfacial nanostructure in graphene-based electrochemical storage devices where ionic liquids (ILs) are used as electrolytes. In this contribution, the impact of the anions of imidazolium-based ILs on the IL–graphene interface as well as on the electronic structure of graphene is investigated. Raman spectroscopy unveils that 1-butyl-3-methylimidazolium ILs having smaller anions induce n-type doping, while ILs with larger anions have a negligible effect on the doping. Molecular modeling simulations reveal that changes in the electrostatic potential at the IL–graphene interface are responsible for the n-type doping.

Configuration of the active region for the Ge-on-Si photodetector based on carrier mobility

The design of vertical and lateral PIN Ge-on-Si photodetectors was motivated by the disparity in electron and hole mobilities. In the case of vertical PIN junction detectors, configuring the slab region as n-type doping leads to a notable increase in the bandwidth of approximately 20 GHz compared to utilizing p-type doping for the slab. For lateral PIN junction detectors, we determined that setting the length of the n-type slab region to be 2.8 times that of the p-type slab region, based on the carrier saturation drift rate ratio, does not compromise the bandwidth. This configuration enhances the bandwidth while minimizing light absorption loss from the electrode. The proposed design in this study enhances the performance of Ge-on-Si photodetectors without adding complexity to the fabrication process. The principles applied in this study serve as instructive references for the conceptualization of other photonic or electronic devices, reinforcing the widespread applicability of these design strategies.

Three amine derivative/graphene oxide van der Waals heterostructures for the photocatalytic detoxification of As(III)

Although van der Waals heterostructures (vdWHs) have suggested the considerable advantages in engineering photoelectronic properties, it remains the limited understanding for the roles of typical nitrogen configurations in vdWHs. Herein, pyrrolic N, pyridinic N, and graphitic N, are introduced into the vdWHs via assembling indole, quinoline, and indolizine with graphene oxide (GO). Pyrrolic N prefers to adhere to the hydroxyls on GO surface, pyridinic N is apt to be immobilized by the carboxyls, and graphitic N shows poor affinitive selectivity. Both pyrrolic and pyridinic N introduce new π→π* orbitals into the resulted vdWHs, while, graphitic N leads to an obvious decay of n→π* transition. All amine derivatives in the vdWHs inject electrons into the conduction band of GO to provide n-type doping, which leads to decreased bandgaps. The decreasing conductivities are observed in all vdWHs, which is temporarily ascribed to the unfavorable electronic correlations at the van der Waals interfaces. By contrast, pyrrolic N contributes more electrons to GO, which enables In-GO to exhibit stronger photocurrent response (almost 7 times as much as the other heterostructures and GO) and higher photocatalytic activity for oxidating As(III) (6.8, 3.6, and 2.0 times than Qu-GO, GO and Iz-GO, respectively).

Development and Analysis of Graphene-Sheet-Based GaAs Schottky Solar Cell for Enriched Efficiency.

Comparative studies of the 2D numerical modelling and simulation of graphene-based gallium arsenide and silicon Schottky junction solar cell are studied using TCAD tools. The performance of photovoltaic cells was examined while taking parameters, such as substrate thickness, relationship between transmittance and work function of graphene, and n-type doing concentration of substrate semiconduction. The area with the highest efficiency for photogenerated carriers was found to be located near the interface region under light illumination. The significant enhancement of power conversion efficiency was shown in the cell with a thicker carrier absorption Si substrate layer, larger graphene work function, and average doping in a silicon substrate. Thus, for improved cell structure, the maximum JSC = 4.7 mA/cm2, VOC = 0.19 V, and fill factor = 59.73% are found under AM1.5G, exhibiting maximum efficiency of 6.5% (1 sun). The EQE of the cell is well above 60%. This work reports the influence of different substrate thickness, work function, and N-type doping on the efficiency and characteristics of graphene-based Schottky solar cells.

Direct Observation of Contact Reaction Induced Ion Migration and its Effect on Non-Ideal Charge Transport in Lead Triiodide Perovskite Field-Effect Transistors.

The migration of ionic defects and electrochemical reactions with metal electrodes remains one of the most important research challenges for organometal halide perovskite optoelectronic devices. There is still a lack of understanding of how the formation of mobile ionic defects impact charge carrier transport and operational device stability, particularly in perovskite field-effect transistors (FETs), which tend to exhibit anomalous device characteristics. Here, the evolution of the n-type FET characteristics of one of the most widely studied materials, Cs0.05 FA0.17 MA0.78 PbI3, is investigated during repeated measurement cycles as a function of different metal source-drain contacts and precursor stoichiometry. The channel current increases for high work function metals and decreases for low work function metals when multiple cycles of transfer characteristics are measured. The cycling behavior is also sensitive to the precursor stoichiometry. These metal/stoichiometry-dependent device non-idealities are correlated with the quenching of photoluminescence near the positively biased electrode. Based on elemental analysis using electron microscopy the observations can be understood by an n-type doping effect of metallic ions that are created by an electrochemical interaction at the metal-semiconductor interface and migrate into the channel. The findings improve the understanding of ion migration, contact reactions, and the origin of non-idealities in lead triiodide perovskite FETs.

Electronic Impurity Doping of a 2D Hybrid Lead Iodide Perovskite by Bi and Sn

Control over conductivity and carrier type (electrons and holes) defines semiconductors. A primary approach to target carrier concentrations involves introducing a small population of aliovalent impurity dopant atoms. In a combined synthetic and computational study, we assess impurity doping by introducing Bi and Sn into the prototype 2D Ruddlesden-Popper hybrid perovskite phenylethylammonium lead iodide (PEA2PbI4). Experimentally, we demonstrate that Bi and Sn can achieve n- and p-type doping, respectively, but the doping efficiency is low. Simulations show that Bi introduces a deep defect energy level (∼0.5 eV below the conduction band minimum) that contributes to the low doping efficiency, but, to reproduce the low doping efficiency observed experimentally, an acceptor level must also be present that limits n-type doping. Experiments find that Sn achieves p-dopant behavior and simulations suggest that this occurs through the additional oxidation of Sn defects. We also study how substitutional Bi incorporation can be controlled by tuning the electrochemical environment during synthesis. First-principles impurity doping simulations can be challenging; typical dopant concentrations constitute less than 0.01% of the atoms, necessitating large supercells, while a high level of theory is needed to capture the electronic levels. We demonstrate simulations of complex defect-containing unit cells that include up to 3383 atoms, employing spin-orbit coupled hybrid density functional theory. While p- and n-type behavior can be achieved with Sn and Bi, simulations and experiments provide concrete directions where future efforts must be focused to achieve higher doping efficiency.Received 5 December 2022Revised 28 April 2023Accepted 4 May 2023DOI:https://doi.org/10.1103/PRXEnergy.2.023010Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the National Renewable Energy Laboratory (NREL) Library, part of a national laboratory of the U.S. Department of Energy.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasEnergy materialsSolar energyEnergy Science & Technology

Synthesis and Thermoelectric Properties of La-doped n-type Mg3SbBi Materials

Mg3Sb2-based materials are very promising for thermoelectric applications at low temperatures, and are strong candidates to replace n-type Bi2Te3 for cooling and power generation. Substituting Sb atoms with chalcogen elements (S, Se, Te) is a typical method of n-type doping, while doping the Mg site with Group 3 elements (Y, Sc) and Lanthanides has also been studied. Unique advantages have been recently reported. In this study, a La-containing compound, LaSb, was used to fabricate n-type Mg3SbBi. The thermoelectric properties of polycrystalline Mg3LaxSbBi (0 ≤ <i>x</i> ≤ 0.02) were investigated after synthesis by sequential processes of arc melting, ball milling, and spark plasma sintering. Undoped Mg3SbBi is p-type with poor thermoelectric performance, and switched to n-type with La doping. The electron concentration of Mg3LaxSbBi increased linearly with La content <i>x</i>, reaching up to 9.4 × 10<sup>19</sup> cm<sup>-3</sup> at <i>x</i> = 0.02. The power factor and the figure of merit were also maximized in Mg3La0.02SbBi, reaching 1.8 mW m<sup>-1</sup>K<sup>-2</sup> (573 K) and 0.89 (623 K), respectively. The lattice thermal conductivity decreased with increasing La content above ~500 K, and the minimum value of 0.73 W m<sup>-1</sup>K<sup>-1</sup> was obtained in Mg3La0.02SbBi. This study shows that La doping using LaSb provides a reliable method for n-type doping of Mg3Sb2-based materials.

Preparation of degenerate n-type AlxGa1−xN (0 < x ≤ 0.81) with record low resistivity by pulsed sputtering deposition

Highly conductive AlGaN alloys hold a great technological potential, wherein the degenerate n-type doping is key in reducing parasitic resistances in electronic and opto-electronic devices. Nonetheless, AlxGa1−xN elaborated in conventional methods exhibits degraded electron concentration at high Al compositions. Here, we demonstrated the growth of degenerate n-type AlxGa1−xN (0 < x ≤ 0.81) with record high electron concentrations by using the pulsed sputtering deposition (PSD) method. The fabricated samples were investigated by cathodoluminescence and Hall-effect measurements in studying the related deep-level emission and electron mobility, respectively. Our findings showed that the PSD-grown heavily Si-doped AlxGa1−xN exhibits record low resistivity values: 2.5 × 10−3 Ω cm with an electron concentration of 1.2 × 1020 cm−3 for x = 0.60 and 1.7 × 10−2 Ω cm with an electron concentration of 3.2 × 1019 cm−3 for x = 0.81. Temperature-dependent Hall-effect measurements confirmed the degenerate nature of heavily Si-doped AlxGa1−xN up to x = 0.81. These results clearly show that the PSD n-type AlGaN is quite promising for reducing parasitic resistance in AlGaN based far UVC light-emitting devices and high breakdown voltage electron devices.

Electrochemical Doping of Halide Perovskites by Noble Metal Interstitial Cations.

Metal halide perovskites are an attractive class of semiconductors, but it has proven difficult to control their electronic doping by conventional strategies due to screening and compensation by mobile ions or ionic defects. Noble-metal interstitials represent an under-studied class of extrinsic defects that plausibly influence many perovskite-based devices. In this work, doping of metal halide perovskites is studied by electrochemically formed Au+ interstitial ions, combining experimental data on devices with a computational analysis of Au+ interstitial defects based on density functional theory (DFT). Analysis suggests that Au+ cations can be easily formed and migrate through the perovskite bulk via the same sites as iodine interstitials (Ii + ). However, whereas Ii + compensates n-type doping by electron capture, the noble-metal interstitials act as quasi-stable n-dopants. Experimentally, voltage-dependent, dynamic doping by current density-time (J-t), electrochemical impedance, and photoluminescence measurements are characterized. These results provide deeper insight into the potential beneficial and detrimental impacts of metal electrode reactions on long-term performance of perovskite photovoltaic and light-emitting diodes, as well as offer an alternative doping explanation for the valence switching mechanism of halide-perovskite-based neuromorphic and memristive devices.

Dissociative Host-Dopant Bonding Facilitates Molecular Doping in Halide Perovskites

Molecular doping is a promising strategy to fine-tune the electronic properties of halide perovskites and accelerate their implementation in next-generation optoelectronics. However, a deeper understanding of the role of host-dopant interactions in these systems is needed to fully exploit the potential of this avenue. Herein, we demonstrate a surface post-treatment strategy employing n-type molecular dopant n-DMBI-H to modulate free hole density in p-type CH3NH3Sn0.75Pb0.25I3 films. We show that the adsorption of n-DMBI-H on surface Sn atoms, followed by the dissociation of an electron-donating hydride from the dopant, facilitates charge transfer to the perovskite and hole trapping at the dissociated hydride. We identify this mechanism as a key factor dictating doping compensation in perovskites, allowing carrier density control within nearly 1 order of magnitude via the dissociated molecular dopant located at film surfaces and grain boundaries. We then exploit n-DMBI-H in perovskite/transport layer junctions, achieving reduced carrier losses and improved contact selectivity and performance in p-i-n, Sn-rich perovskite solar cells. We expect this work to provide carrier density tuning guidelines for a broad range of tin-based perovskite applications.

Regulating the p-n interface quality for Sb2Se3-based quasi-homojunction thin film solar cells by an effective two-step heat treatment process

Earth-abundant Sb2Se3 material has received an increased attention from photovoltaics community thanks to its excellent photo-electronic properties. Despite the fact that the Sb2Se3 heterojunction solar cells have obtained a rapid development, the serious interface defects have not been fundamentally solved so far. By contrast, the quasi-homojunction has advantages over heterojunction in terms of electronic property, however, its development is quite slow. Herein, the Sb2Se3-based quasi-homojunction devices with the configuration of SLG/FTO/Cu-Sb2Se3/I-Sb2Se3/Al have been fabricated using magnetron sputtering accompanied by a two-step heat treatment process. The relationship between the p-n interface quality and the device performances was investigated in detail. Thanks to the very well p-n interface, the devices achieved a 2.64% PCE, with ∼ 10% improvement compared with the devices fabricated via one-step heat treatment, as previous reported. Moreover, an effective p- and n-type doping with high carrier density is essential for fabricating the efficient p-n interface, as evidenced by SCAPS simulations. Through the co-optimization of various device parameters, the predicted PCE of quasi-homojunction devices can reach 18.96%, using the Mg as back contact, leading to lower minority carrier recombination at near the back-contact. Eventually, the simulation indicated clearly the directions for further promoting cell performances by doping strategy. This work can provide valuable guidance for the further development and improvement of Sb2Se3-based quasi-homojunction thin-film solar cells.

Evaluation of Crystal Quality and Dopant Activation of Smart Cut<sup>TM</sup> - Transferred 4H-SiC Thin Film

The Smart CutTM process offers an advantageous opportunity to provide a large number of performance-improved SiC substrates for power electronics. The crystalline quality and the electrical activation of the 4H-SiC transferred layer are then at stake when it comes to the power device reliability. In this study, we find that the H+ ion implantation used for the Smart CutTM process leads to electrical deactivation of dopants and partially disorders the material. The transferred layer fully recovers its initial crystalline quality after a 1300°C anneal, with no further evolution beyond this temperature. At this point however, the n-type dopants are still inactive. The dopant reactivation occurs in the same temperature range than that of implanted nitrogen: between 1400°C and 1700°C. After 1700°C, the initial doping level of bulk SiC is recovered.

Improving the Performance of Layer-by-Layer Processed Organic Solar Cells via Introducing a Wide-Bandgap Dopant into the Upper Acceptor Layer.

The layer-by-layer (LbL) solution-processed organic solar cells (OSCs) are conductive to achieve vertical phase separation, tunable donor-acceptor (D/A) interfaces, and favorable charge-transport pathways. In this work, a wide-bandgap component poly(9-vinylcarbazole) (PVK) is added to the upper electron acceptor layer to improve the performance of LbL-processed OSCs. Results show that the PVK component can adjust the film morphology, dope the electron acceptor, increase the electron concentration, and improve charge transport. Such n-type doping is verified by Seebeck coefficient measurement, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance characterization. In addition, the fluorescence intensity and exciton lifetime of the PVK-doped acceptor film are increased, thus being beneficial for exciton diffusion to the D/A interface. Therefore, the power conversion efficiency (PCE) of LbL OSCs increases when 2.50 wt.% PVK is employed in the electron acceptor layer of commonly-used high-efficiency system and a maximum value of 19.05% can be achieved. The role of PVK played in the active layer is different from those of additives and ternary components reported previously, so the results provide an alternative way to enhance the device performance of LbL-processed OSCs.

1.5 µm wavelength NPN-type photonic-crystal surface-emitting laser exceeding 100 mW.

A 1.5 µm laser diode has applications in eye-safe light detection and ranging (LiDAR) and optical communications via photonic integrated circuits. Photonic-crystal surface-emitting lasers (PCSELs) have lens-free applications in compact optical systems because of narrow beam divergences (<1 degree). However, the output power has still been less than 1 mW for 1.5 µm PCSELs. For higher output power, one approach is suppression of p-dopant Zn diffusion in the photonic crystal layer. Therefore, n-type doping was used for the upper crystal layer. Moreover, an NPN-type PCSEL structure was proposed to reduce intervalence band absorption in the p-InP layer. Here, we demonstrate a 1.5 µm PCSEL with 100 mW output power, which exceeds previous reported values by two orders of magnitude.

Prediction and Synthesis of a Selenide Perovskite for Optoelectronics

The advent of halide perovskites in recent years has opened an avenue for redeveloping perovskite materials as semiconductors. In the quest for semiconducting perovskites, chalcogenides, which exhibit higher stability than their halide siblings and often direct band gaps for optoelectronics, have attracted more and more attention. So far, functional chalcogenide perovskites have been exclusively sulfides. Here, employing first-principles calculations and the criterion of phase stability in addition to the commonly used thermodynamic and dynamical criteria, we precisely predict the existence of LaScSe3 as a thermodynamically stable selenide perovskite, which is validated by our experimental synthesis. Combining hybrid functional and many-body quasi-particle (G0W0 and Bethe–Salpeter equation) calculations, we predict that LaScSe3 is a direct-gap semiconductor having the band gap in the green-to-blue region and capable of p- and n-type bipolar doping, potentially for optoelectronic applications.

The Synergistic Effect of Triazine and Phosphaphenanthrene Units on the Physico-Chemical Behavior of Polyimides.

With the aim to develop polymers with appealing, multifunctional characteristics, a series of polyimides were designed by anchoring 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) units on the main polymer chains containing 1,3,5-triazine and several flexible moieties, such as ether, hexafluoroisopropylidene, or isopropylidene. A detailed study was conducted to establish structure-property correlations, with a focus on the synergistic effectiveness of triazine and DOPO moieties on the overall features of polyimides. The results evidenced good solubility of the polymers in organic solvents, their amorphous nature with short-range regular-packed polymer chains, and high thermal stability with no glass transition temperature below 300 °C. Spectrophotometric measurements revealed the existence of a strong charge transfer complex in these polymers that led to a "black" appearance, which generated broad absorption bands spanning on the overall visible range. Nevertheless, these polymers displayed green light emission associated with 1,3,5-triazine emitter. The electrochemical characteristics of the polyimides in solid state demonstrated their strong n-type doping character induced by three different structural elements with electron-acceptance capability. The useful properties of these polyimides, including optical, thermal, electrochemical, aesthetics, and opaqueness, endow them with several possible applications in the microelectronic field, such as protecting layers for the inner circuits against UV light deterioration.

Degenerate p-Type and n-Type Doping of Diamane by Molecular Adsorption

Motivated by the successful synthesis of two-dimensional diamane [Nat. Nanotechnol. 2020, 15, 59-66], in this work, the electronic and optical properties of diamane with molecular adsorption are investigated by first-principles calculation. Based on the surface transfer doping mechanism, we report the degenerate p-type and n-type doping for hydrogenated diamane (H-diamane) and fluorinated diamane (F-diamane), respectively. Hole accumulation on H-diamane and degenerate levels in the density of states (DOS) are found when organic molecules (tetracyanoethylene, tetracyanoquinodimethane, and tetrafluorotetracyanoquinodimethane) and transition-metal oxides (MoO3, CrO3, WO3, V2O5, and ReO3) are chosen as acceptors on H-diamane. Conversely, F-diamane shows electron accumulation and degenerate levels in DOS when organic molecules (decamethylcobaltocene and cobaltocene2) are adsorbed. The carrier concentration values of H-diamane and F-diamane are 1.91 × 1013 to 3.96 × 1013 cm–2 and 1.96 × 1013 to 3.38 × 1013 cm–2, respectively. After adsorption, the optical absorption increases significantly in the visible-light region. Our findings would provide a feasible route to modulate the electronic and optical properties of diamane.

Comparative Thermoelectric Properties of Polypropylene Composites Melt-Processed Using Pyrograf® III Carbon Nanofibers

The electrical conductivity (σ) and Seebeck coefficient (S) at temperatures from 40 °C to 100 °C of melt-processed polypropylene (PP) composites filled with 5 wt.% of industrial-grade carbon nanofibers (CNFs) is investigated. Transmission Electron Microscopy (TEM) of the two Pyrograf® III CNFs (PR 19 LHT XT and PR 24 LHT XT), used in the fabrication of the PP/CNF composites (PP/CNF 19 and PP/CNF 24), reveals that CNFs PR 24 LHT XT show smaller diameters than CNFs PR 19 LHT XT. In addition, this grade (PR 24 LHT XT) presents higher levels of graphitization as deduced by Raman spectroscopy. Despite these structural differences, both Pyrograf® III grades present similar σ (T) and S (T) dependencies, whereby the S shows negative values (n-type character). However, the σ (T) and S (T) of their derivative PP/CNF19 and PP/CNF24 composites are not analogous. In particular, the PP/CNF24 composite shows higher σ at the same content of CNFs. Thus, with an additionally slightly more negative S value, the PP/CNF24 composites present a higher power factor (PF) and figure of merit (zT) than PP/CNF19 composites at 40 °C. Moreover, while the σ (T) and S (T) of CNFs PR 19 LHT XT clearly drive the σ (T) and S (T) of its corresponding PP/CNF19 composite, the S (T) of CNFs PR 24 LHT XT does not drive the S (T) observed in their corresponding PP/CNF24 composite. Thus, it is inferred in PP/CNF24 composites an unexpected electron donation (n-type doping) from the PP to the CNFs PR 24 LHT XT, which could be activated when PP/CNF24 composites are subjected to that increase in temperature from 40 °C to 100 °C. All these findings are supported by theoretical modeling of σ (T) and S (T) with the ultimate aim of understanding the role of this particular type of commercial CNFs on the thermoelectrical properties of their PP/CNF composites.

Thermoelectric performance of Mg2.2(Ge0.9Sn0.1) ternary solid solution doped with Ag, Bi, Ni and Sb

Mg2.2(Ge0.9Sn0.1)0.94X0.06(X = Ag, Bi, Ni, Sb) ternary solid solutions were synthesized using a two-step solid state reaction followed by hot pressing. The effects elemental doping on thermoelectric properties of these compounds were studied in the temperature range of 300 to 800 K. The findings demonstrate that Bi, Sb, and Ni function as useful n-type dopants, with Bi being more efficiently in the solid solution of Mg2.2Ge0.9Sn0.1. Additionally, the findings indicate that Ag is less efficient in n-type doping. Finally, maximum ZT for the Bi-doped sample is 0.82 at 800 K because of its strong electrical conductivity and moderate Seebeck coefficient.