Deep Energy Levels Research Articles

Role of native defects on the opto-electronic properties of p-type ZnO synthesized during the most straightforward method: only water

The influence of predominant native defects in forming ZnO with p-type conductivity is discussed in this work when the semiconductor is synthesized only in water. The semiconductor was prepared by dissolving a Zn-salt in deionized water at 80 °C. The powders were thermally treated at 400 °C in an air atmosphere to obtain well-defined crystalline ZnO. XRD, SEM, EDS, Raman spectroscopy, diffuse reflectance, photoluminescence, and Seebeck effect techniques were used to characterize the synthesized material. The results showed a well-crystalline semiconductor in wurtzite phase. The crystal-oriented growth was the (002) plane. The sample morphology was formed by highly ordered sticks-like. The optoelectronic characterization showed that the synthesized ZnO had a lower band gap than that reported in the literature. It was related to deep energy levels corresponding to oxygen interstitials as the predominant native defects. Raman, EPR, and photoluminescence spectra analysis corroborated the existence of native defects in the crystalline structure. The p-type conductivity of the sample was determined by Seebeck coefficient analysis. A synthesis reaction mechanism involving the formation of oxygen interstitials was proposed in this work. Understanding the effects of native defects in wide band gap semiconductors is necessary to design new materials for sensors or energy conversion applications.

Fused phthalimide-based A–DA′D–A small molecule: New protocol for n-type organic semiconductors

Development of well-conjugated building blocks by a concise and efficient synthetic procedure is crucial for organic electronics. In particular, for A–DA′D–A-type (A = donor and D = acceptor) organic semiconductors, which are the most popular and successful small molecular acceptors, the limited number DA′D fused cores limits the variety of these molecules. Herein, we report a new A–DA′D–A-type small molecule, TIIC, containing an entirely new DA′D fused core. The complete synthetic procedure, including a well-designed photocyclization step, resulted in above 50% total yield over five steps. TIIC shows strong light absorption in the complete visible region because of the extended π-conjugation and strong intramolecular charge transfer. The deep lowest unoccupied molecular orbital energy level (−4.0 eV) of TIIC, which indicates the n-type semiconductor property, was further confirmed by the organic field-effect transistor performance with unipolar electron mobility of 3.51 × 10−4 cm2 V−1 s−1.

Effects of defects on electrical transport properties of anatase TiO<sub>2</sub> polycrystalline under high pressure: AC impedance measurement

The electrical transport properties of anatase TiO<sub>2</sub> polycrystalline have been systematically investigated by using high pressure <i>in-situ</i> impedance spectroscopy measurements. The anomalous behaviors of resistance, parameter factor and relaxation frequency of grain and grain boundary can be found at 6.4, 11.5 and 24.6 GPa. The results indicate that the first two discontinuous points (6.4 and 11.5 GPa) correspond to the phase transitions of TiO<sub>2</sub> from anatase to α-PbO<sub>2</sub> and then to baddeleyite, respectively. Above 24.6 GPa, TiO<sub>2</sub> completely transforms into the baddeleyite phase. Based on the change of grain resistance and grain boundary resistance under pressure, intrinsic defects play a crucial effect in the electrical transport properties of TiO<sub>2</sub> at high pressures. At 6.4 GPa, the occurrence of phase transition gives rise to the variation of defects’ role, from a deep energy level defect (as a recombination centre) changes into a shallow energy level defect (providing carriers for the conduction and valence bands). In addition, the position of defect in energy band changes with pressure increasing. The phase transition of TiO<sub>2</sub> at 6.4 GPa is the rearrangement of TiO<sub>6</sub> octahedron, while the other one at 11.5 GPa can be attributed to the migration of oxygen Schottky defects from inner to surface. Combining the packing factor and relaxation frequency, the electrical transport properties of TiO<sub>2</sub> under pressure are revealed, the packing factor and the relaxation frequency are closely related to the mobility and the carrier concentration, respectively. The activation energy of grain and grain boundary decrease with the pressure elevating, indicating that the transport of carriers in grain and grain boundary become easier under pressure, and the former is smoother than the latter owing to the activation energy of grain being smaller than that of grain boundary in the same pressure range. Moreover, the relaxation frequency ratio of TiO<sub>2</sub> grain and TiO<sub>2</sub> grain boundary decreases with pressure increasing, and the grain boundary effect under high pressure is not obvious.

Defects Passivation via Potassium Iodide Post‐Treatment for Antimony Selenosulfide Solar Cells with Improved Performance

AbstractAntimony selenosulfide (Sb2(S,Se)3) has been emerging as a promising light absorber in the past few years owing to tunable bandgap (1.1–1.7 eV), high absorption coefficient (>105 cm−1) and excellent phase and environmental stability. However, the efficiency of Sb2(S,Se)3 solar cells lags far behind the Shockley–Queisser limit. One of the critical obstacles originates from various extrinsic and intrinsic defects. They mostly locate in the deep energy levels and are prone to form recombination centers, inhibiting the improvement of device performance. Herein, surface post‐treatment via potassium iodide is introduced to fabricate high‐quality Sb2(S,Se)3 films and solar cells. The surface post‐treatment not only manipulates the crystal growth process to form compact films with larger grain size but also forms better band alignment and inhibits the formation of deep‐level defects antimony antisite (SbSe), thus improving the quality of heterojunction. Consequently, the resultant Sb2(S,Se)3 solar cells achieve a champion power conversion efficiency of 9.22%. This study provides a new strategy of passivating deep‐level intrinsic defects via surface post‐treatment for high‐efficiency Sb2(S,Se)3 solar cells.

Halogen-Free -Conjugated Polymers Based on Thienobenzobisthiazole for Efficient Nonfullerene Organic Solar Cells: Rational Design for Achieving High Backbone Order and High Solubility.

In -conjugated polymers, a highly ordered backbone structure and solubility are always in a trade-off relationship that must be overcome to realize highly efficient and solution-processable organic photovoltaics (OPVs). Here, it is shown that a -conjugated polymer based on a novel thiazole-fused ring, thieno[2',3':5,6]benzo[1,2-d:4,3-d']bisthiazole (TBTz) achieves both high backbone order and high solubility due to the structural feature of TBTz such as the noncovalent interlocking of the thiazole moiety, the rigid and bent-shaped structure, and the fused alkylthiophene ring. Furthermore, based on the electron-deficient nature of these thiazole-fused rings, the polymer exhibits deep HOMO energy levels, which lead to high open-circuit voltages (VOC s) in OPV cells, even without halogen substituents that are commonly introduced into high-performance polymers. As a result, when the polymer is combined with a typical nonfullerene acceptor Y6, power conversion efficiencies of reaching 16% and VOC s of more than 0.84V are observed, both of which are among the top values reported so far for "halogen-free" polymers. This study will serve as an important reference for designing -conjugated polymers to achieve highly efficient and solution-processable OPVs.

Effects of post-deposition annealing temperatures in argon ambient on structural, optical, and electrical characteristics of RF magnetron sputtered gallium oxide films

Different post-deposition annealing temperatures were carried out in argon ambient to investigate the corresponding effects onto structural, morphological, optical, and electrical characteristics of RF magnetron sputtered gallium oxide (Ga2O3) films. Cubic phase of γ-Ga2O3 was transformed to mixed phases of cubic and monoclinic phases of β-Ga2O3 as the temperature was increased from 400 to 800 °C before became fully β-Ga2O3 phases at 1000 °C. Oxygen vacancies and oxygen interstitials were formed, generating deep energy levels in band gap of the Ga2O3 films. Findings revealed the acquisition of the highest current density in the Ga2O3 film annealed at 400 °C as a consequence of the highest density (J) of dislocation and oxygen vacancies in the film. Nonetheless, the formation of a thicker interfacial layer and location of oxygen vacancies in the film annealed at 1000 °C have caused minute increase in the J surpassing that of 800 °C at a gate voltage greater than 15 V.

Photochromism of TiO2 Nanoparticles Doped with Molybdenum Ions: Neutral Color Change from Colorless to Black via Gray.

Transition metal oxide nanoparticles have been extensively studied for the development of smart windows which are expected to be a promising technology to save energy in buildings. However, most of them turn blue under UV irradiation. Since the blue coloration affects the color of objects through the windows, the development of materials with a neutral color which hardly disturbs the view is more beneficial. In this work, we prepared a colorless-transparent TiO2 colloidal solution containing Mo6+ ions (Mo-TiO2), which turns black via gray in a nitrogen atmosphere under UV irradiation. An absorption peak was observed at 535 nm, which increased with an increase in the UV irradiation time and reached a constant value (Absmax). The Absmax value increased linearly with an increase in the Mo doping amount. We demonstrated that the photochromic behavior of the Mo-TiO2 nanoparticles is completely different from that of pure MoO3 or the mixture of MoO3 and TiO2. In addition, we performed a kinetic study to elucidate the mechanism and found that the coloration rate at the initial stage decreased with an increase in Mo doping amount. Based on the kinetic analysis, the following results are obtained: a color center is formed at a deeper energy level than the Mo dopant level; the number of the color center depends on the Mo doping amount, and the color center traps the photogenerated electrons more rapidly when it is isolated. The black color was bleached by purging the air in the solution. In particular, the gray state which is observed as a transient color is promising for the development of smart windows to shield the sunlight while allowing a clear and undistorted view.

Semiconducting Behaviour and Corrosion Resistance of Passive Film on Corrosion-Resistant Steel Rebars.

Chloride-induced corrosion of steel rebars is one of the major causes of the premature failures of reinforced concrete structures served in different environments. This paper investigates the semiconducting behaviour and corrosion resistance of the passive film formed on the corrosion-resistant rebars exposed to simulated concrete pore solutions with different pH values and chloride concentrations. The electronic properties of the passive film were studied using potentiodynamic measurements and capacitance measurements (Mott-Schottky analysis). The results indicate that, firstly, the passive film of corrosion-resistant steel rebar shows n-type semiconducting behaviour with shallow and deep donor states in the band gap during passivation, and the deep donor energy level of corrosion-resistant steel rebar passive film is not sensitive to the decreasing pH value; secondly, under the same conditions, the passive film of corrosion-resistant rebars has a larger negative flat-band potential and thicker space charge layer than hot-ribbed rebars; thirdly, n-type semi-conductivity at a higher potential disappears once the chloride concentration at the rebar surface attains the chloride threshold value; and finally, a reverse charge layer forms on the surface of CR rebar at 0.50 V potential.

N-Annulated Perylene Bisimide-Based Double-Cable Polymers with Open-Circuit Voltage Approaching 1.20 V in Single-Component Organic Solar Cells.

In this work, we have introduced single/double-sided N-annulated perylene bisimide (PBI) with deep energy levels into double-cable polymers with poly[1-(5-(4,8-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b']dithiophen-2-yl)thiophen-2-yl)-5,7-bis(2-ethylhexyl)-3-(5-methylthiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c']dithiophene-4,8-dione] (PBDB-T-Cl) as a donor backbone, marking as s-PPNR and as-PPNR, according to the molecular symmetry. Both double-cable polymers displayed a high open-circuit voltage approaching 1.20 V in light of high energy level discrepancy between electron-donating and electron-withdrawing parts, which is the highest open-circuit voltage among double-cable-based single-component organic solar cell (SCOSC) devices. Additionally, the asymmetric polymer displayed improved absorption spectra, thereby promoting crystallization and phase separation. Consequently, the as-PPNR-based SCOSCs achieved a power conversion efficiency of 5.05% along with a higher short-circuit current density and fill factor than their s-PPNR-based counterparts. In this work, we have successfully incorporated N-annulated PBI into double-cable polymers and revealed the important effects on structural symmetry and phase separation of double-cable polymers for higher SCOSC performance.

Enhanced Photovoltaic Performance of Benzothiadiazole‐Based Polymers by Controlling their Backbone Planarity for Organic Solar Cells

AbstractHere, a new synthetic strategy for converting low‐energy benzo[c][1,2,5]thiadiazole (BT)‐based polymers into efficient polymeric donors for non‐fullerene acceptor‐based organic solar cells (NFA–OSCs) is demonstrated. A highly planar 5,6‐difluoro‐benzo[c][1,2,5]thiadiazole (ffBT)‐based alternating polymer, P1, comprising of electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene (BDTT) and strong electron‐deficient 5,6‐difluoro‐4,7‐bis(4‐octylthiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (DTffBT) units is prepared. Additionally, two ternary polymers, P2 and P3, are preparedby replacing 25% and 50% of the DTffBT unit on the P1 backbone with a weak electron‐deficient 2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (DTPPD) unit, which has a twisted but well‐controlled wavy backbone. The properties of the resulting polymers, P1–P3, are investigated to understand the effects of changing the planarity and curvature of the backbone of the BT‐based polymers. Notably, increasing the concentration of the DTPPD unit on P1 results in ablue‐shift in absorption band and relatively deep energy levels. Further, the π–π stacking of the polymers is decreased by increasing the amount of DTPPD units on P1. The NFA–OSCs fabricated using P1–P3 as the electron donor afford maximum power conversion efficiencies (PCE) of 2.46%, 4.52%, and 7.54%, respectively. Overall, the photovoltaic performance of the BT‐based polymers is significantly improved by lowering their planarity and/or changing their backbone curvature.

High Efficiency Inorganic Perovskite Solar Cells Based On Low Trap Density and High Carrier Mobility CsPbI3 Films

AbstractInorganic perovskite CsPbI3 has exhibited promising performance in single‐junction solar cells, but the grain boundaries (GBs) in its film cause the formation of the defects with deep energy levels (such as iodide vacancy (VI)) and impede the transport of carriers, worsening the efficiency and stability of the solar cells. Here, a CsPbI3 precursor is devised with thiophenol series ligands (TP‐ligands) containing both SH and π‐conjugated molecules. The strong interaction between the SH group (Lewis base) and PbI2 (Lewis acid) suppresses the formation of PbI42− in perovskite solution, thus suppressing the formation of VI in the film accordingly. The terminal groups, such as ‐F and ‐NH2, are employed to achieve an appropriate evaporation speed of the ligands and prevent the oxidation of the thiophenol group, then a high‐quality perovskite film with low trap density is obtained. In addition, the functional group π‐conjugated molecules provide additional carrier transmission channels at the GBs to increase carrier mobility, which facilitates the exciton separation and prolongs the charge lifetime. The CsPbI3 solar cell shows a considerable power conversion efficiency of 20.1% with an open‐current voltage of 1.18 V and a high fill factor of 83.5% and excellent working stability.

Material Defects and Dark Currents in InGaAs/InP Avalanche Photodiode Devices

An In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/indium phosphide (InP) avalanche photodiode (APD) with a separate absorption, grading, charge, and multiplication (SAGCM) structure is epitaxially grown by molecular beam epitaxy (MBE). The resulting material is studied using X-ray diffraction (XRD), photoluminescence (PL), and scanning transmission electron microscopy. The activation energy extracted from the dark current of the APD indicates that it is dominated by the generation–recombination (G–R) process. Deep low-temperature PL peaks reveal the existence of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{v} + 0.42$ </tex-math></inline-formula> -eV deep energy level defect in the indium–gallium–arsenide (InGaAs) absorber layer, which is considered to be a result of point defects caused by Ga-poor or In-poor MBE growth conditions. The effect of the defect on the dark current is confirmed using numerical calculation methods.

Electrical characterization and extraction of activation energies of the defect states in the LaAlO3/SrTiO3 heterostructure

In this work, we study the electronic properties of defects in the LaAlO3/SrTiO3 heterostructure, which is known to host a high mobility two-dimensional electron gas (2DEG) at the interface. This 2DEG also shows photoconductance, which could be related to defects that act as deep center trapping and releasing carriers by interaction with light. This phenomenon has raised an interest for the identification of deep energy levels in the LaAlO3/SrTiO3 heterostructure. We have studied the defect state properties using electrical characterization such as capacitance–voltage (C–V), current–voltage (I–V) measurements, and deep-level transient Fourier spectroscopy (DLTFS). From C–V and I–V analyses, a hysteresis was observed indicating an effect of mobile charges in the LaAlO3. Using DLTFS, we identify three defect states located at around 0.17 eV below conduction band and at 0.23 and 0.26 eV above the valence band. These defect states were attributed to defects in SrTiO3 such as strontium vacancies or titanium vacancies. We identify a fourth defect state having an energy of about 0.69 eV below the conduction band that could be related to oxygen vacancies in LaAlO3 or in SrTiO3. In addition, the observation of an effect of the electric field with DLTFS indicated that oxygen vacancies might be involved in Fowler–Nordheim or trap-assisted tunneling through the LaAlO3 layer.

Low-temperature characteristics and gate leakage mechanisms of LPCVD-SiNx/AlGaN/GaN MIS-HEMTs

In this paper, we systematically investigated the static properties and gate current mechanism of low-pressure chemical vapor deposition-SiNx/AlGaN/GaN metal–insulator–semiconductor-high-electronmobility-transistor (MIS-HEMTs) at cryogenic temperature range from 10 K to 300 K. It is found that the threshold voltage of the device shows a positive shift due to the decreased carrier concentration at low temperature, and both the maximum transconductance and ON-resistance are improved at the low temperatures because of the enhanced electron mobility. Under very low electric field, the gate leakage exhibits ohmic conduction. With increasing forward gate bias, the dominant gate leakage mechanism at temperature below150 K gradually transits into trap-assisted tunneling, participating with a deep trap energy level of 0.73 eV in the SiNx dielectric, to Fowler–Nordheim (FN) tunneling. In contrast, the dominant gate leakage mechanism at temperature above 150 K transits from Poole–Frenkel emission, showing a low trap barrier height of 56 meV in the SiNx dielectric, to Fowler–FN tunneling with increasing forward gate bias. Under high reverse gate bias, carrier-limited gate current becomes the dominated gate leakage mechanism.

Leakage current simulations of Low Gain Avalanche Diode with improved Radiation Damage Modeling

We report precise TCAD simulations of IHEP-IME-v1 Low Gain Avalanche Diode (LGAD) calibrated by secondary ion mass spectroscopy (SIMS). Our setup allows us to evaluate the leakage current, capacitance, and breakdown voltage of LGAD, which agree with measurements’ results before irradiation. And we propose an improved LGAD Radiation Damage Model (LRDM) which combines local acceptor removal with global deep energy levels. The LRDM is applied to the IHEP-IME-v1 LGAD and able to predict the leakage current well at -30 °C after an irradiation fluence of Φeq=2.5×1015neq/cm2. The charge collection efficiency (CCE) is under development.

Chlorinated Conjugated Polymer Based on Chlorine‐ and Cyano‐substituted (E)‐1,2‐Di(thiophen‐2‐yl)ethane for Ambipolar and n‐Type Organic Thin‐film Transistors

Comprehensive SummaryChlorinated conjugated polymers are rarely reported in ambipolar and n‐type organic thin‐film transistors (OTFTs), mainly due to the lack of chlorinated strong electron‐deficient building blocks. Herein, we report three new chlorine (Cl)‐ and cyano (CN)‐ substituted (E)‐1,2‐di(thiophen‐2‐yl)ethane building blocks and their copolymers P2Cl1CNTVT‐DPP, P4Cl1CNTVT‐DPP and P2Cl2CNTVT‐DPP. P2Cl1CNTVT‐DPP and P2Cl2CNTVT‐DPP had nearly planar backbone geometries, mixture of edge‐on and face‐on orientation and deeper energy levels, while P4Cl1CNTVT‐DPP had a twist backbone geometry, face‐on orientation and shallower energy levels. As a result, P2Cl1CNTVT‐DPP exhibited ambipolar characteristic with hole mobility (μh) of 0.70 cm2·V–1·s–1 and electron mobility (μe) of 0.84 cm2·V–1·s–1 and P2Cl2CNTVT‐DPP exhibited n‐type characteristic with μe of 0.64 cm2·V–1·s–1, while P4Cl1CNTVT‐DPP exhibited the lowest μe of 0.36 cm2·V–1·s–1. The devices based on P2Cl2CNTVT‐DPP exhibited good stability after being stored for 10 d in air. The results demonstrate that by rational molecular design, chlorinated polymers with low cost can be applied to high‐performance ambipolar and n‐type OTFTs.

Pyrazinamide photodegradation on NiWO4-palygorskite nanocomposites under polychromatic irradiation.

In this work, antibiotic pyrazinamide (PZA) photodegradation on palygorskite (Pal), NiWO4 crystals, and NiWO4-Pal (2, 6, and 10%) nanocomposites was evaluated under polychromatic irradiation. In the characterization of the samples, XRD patterns displayed good crystallinity for NiWO4 crystals and nanocomposites. In addition, the diffractograms were used in the Rietveld refinement for phase indexing, revealing a wolframite-type monoclinic structure with the space group P2/c. The active vibrational modes related to the characteristic groups of the samples were identified using Raman and FTIR spectroscopy. Photoluminescence (PL) spectra revealed that NiWO4 and NiWO4-Pal (2%) nanocomposite have the highest electron-hole pair recombination rate, and the contribution of the green component in the NiWO4-Pal (2%) nanocomposite indicates a greater contribution of deep energy levels to the PL profile. DRS in the UV-visible region indicated that NiWO4 crystals have indirect band-gap energy (Egap) 2.64 eV; NiWO4-Pal (2, 6, and 10%) nanocomposites have 2.62, 2.58, and 2.59 eV, respectively; and Pal has 2.83 eV. The catalytic tests showed that the NiWO4-Pal (2%) nanocomposite samples, under polychromatic radiation, exhibit greater efficiency in photodegradation at 110 min, with yield of 98.5%. The ROS tests indicated that the studied reactive species play a similar role in PZA photodegradation.

The impacts of charge transfer, localization, and metallicity on hydrogen retention and transport capacity

Solid state hydrides such as early transition metal hydrides are of inestimable importance for the future of hydrogen energy and are actively being investigated for energy conversion and storage applications such as fuel cells, solid-state batteries and neutron moderators. The retention and transport behavior of hydrogen in these hydrides has a huge role on the extended performance of components. While early transition-metal-based compounds exhibit many peculiar properties due to their unique correlated electronic signatures arising from d-orbital electrons, the fundamental chemistry and transport behavior of hydrogen in such hydrides is not well understood. In the present work, using density functional theory, a highly intricate bonding feature is revealed through the theoretical investigation of the electronic structure of early transition metal hydrides YH2 and ZrH2. In particular, a pronounced charge transfer from the transition element to H, results in localized electron densities at deep energy levels. The interplay between intrinsic charge transfer, charge localization, and metallicity in YH2 and ZrH2 leads to strong chemical bonding between metal and hydrogen atoms and large energy barriers for the migration of hydrogen vacancies. Specifically, hydrogen vacancies are found to be stable in the neutral state due to electron screening effects, accompanied by substantially high migration barriers between 0.8–1.2 eV along different crystallographic directions. In contrast, recent literature shows the migration barrier for charged H vacancies in insulating s-block metal hydrides lie between 0.1–0.4 eV, which is suitable for fast conduction applications. This pivotal electron structure difference exploited between early transition metal hydrides and alkali/alkaline earth metal hydrides determines extended hydrogen retention in these early transition metal hydrides. This work explains fundamental differences between the electronic structure of s-block and d-block metal hydrides, and its impact on the mobility of hydrogen vacancies.

Ternary organic solar cells with enhanced charge transfer and stability combining the advantages of polymer acceptors and fullerene acceptors

Organic solar cells (OSCs) based on highly efficient non-fullerene acceptors (NFAs) have recently developed rapidly, and achieved effective charge separation and high open-circuit voltage ( V OC ) under low driving force. Nonetheless, the low driving force inescapably reduces the short-circuit current ( J SC ) and potentially restricts the improvement of external quantum efficiency (EQE). Herein, we introduce the fullerene acceptor PC 71 BM into the efficient NFA system. And the PM6:PY-IT system is selected as a typical NFA system for its high V OC above 0.90 V. Benefiting from the deeper energy level, excellent electron transport characteristic, and unique spherical structure of PC 71 BM, the driving force for charge transfer is effectively improved. Accordingly, the ternary OSC based on PM6:PY-IT:PC 71 BM demonstrates a high efficiency of 16.36%, a much-enhanced J SC of 25.06 mA cm −2 , and the maximum EQE value is successfully increased to 87%, which is superior to binary OSC (efficiency of 14.84%, J SC of 23.10 mA cm −2 and maximum EQE value of 80%). Meanwhile, the introduction of PC 71 BM improves the molecular stacking structure, resulting in excellent stability in non-encapsulated ternary OSCs, which retain 80% initial efficiency after 6 h of continuous illumination treatment and 85% initial efficiency after 33 days of storage (the efficiencies decrease to 68% and 76% respectively in binary OSCs). In addition, similar conclusions can be drawn in another classical NFA system PM6:Y6, with an optimal efficiency of 17.49%. This work proves that PC 71 BM has unique advantages and great research potential in improving the driving force for charge transfer. • The highlights of this work can be summarized as follows: • The PC 71 BM was incorporated into the PM6:PY-IT system to enhance the driving force and construct efficient OSCs. • Benefiting from the enhanced driving force, the maximum EQE and J SC are significantly increased, and the V OC is 0.942 V. • The ternary OSC obtained an optimal efficiency of 16.36%, which is superior to binary OSC (efficiency of 14.84%). • The stability of the non-encapsulated optimized ternary device was improved by the incorporation of PC 71 BM.

Capacitance spectroscopy of thin-film formamidinium lead iodide based perovskite solar cells

This work concerns the interpretation of capacitance spectroscopy results in perovskite-based solar cells. Based on the deep level transient spectroscopy and admittance spectroscopy results, we present arguments that the observable signals in perovskite-based solar cells come from anion migration rather than being a response from deep trap energy levels. The ion migration parameters, such as activation energy and ion concentration, are calculated and compared to theoretical values for different migration paths of ions in perovskites. Those parameters evolve with time, reflecting in the degradation of the cells, which we propose to link with a change in the anion migration path in perovskite. • The same signal is observed in DLTS and admittance spectroscopy. • Its activation energy is in the 0.3 eV–0.5 eV range and decays with time. • Time constants and the presence of large capacitance transients at +1 V point into the diffusion related origin of the signals. • Low activation energy, DLTS sign, comparison with other experiments and theoretical calculations point into anion diffusion. • The observed, dominating signal correlates with the increased shunt of the device.