Phosphorous Emitter Research Articles

Synergistic Enhancement of Emitting Dipole Orientation between Pt‐Based Phosphorescent Sensitizers and Boron‐Based Multi‐Resonance Fluorescent Emitters for High‐Performance Phosphor‐Sensitized Fluorescent Organic Light‐Emitting Diodes

Phosphor‐sensitized fluorescent (PSF) organic light‐emitting diodes (OLEDs) emerge as an attractive solution for realizing high‐performance displays with high color purity, meeting the Broadcast Television 2020 (BT.2020) requirements, by fully harnessing the benefits of both phosphorescent and fluorescent emitters. Herein, the synergistic effect of a Pt sensitizer and a boron (B)‐based multi‐resonance (MR)‐fluorescent emitter are introduced to enhance the efficiency of blue‐emitting PSF–OLEDs. Notably, it is confirmed that the interaction between the empty pz orbital in the boron atom of the MR emitter and the unpaired electrons in the dz2 orbital of the Pt emitter plays a crucial role. The combination results in an enhancement of the horizontal emitting dipole orientation (EDO) to 81%, a marked improvement compared to the individual components of Pt phosphor (69%) or MR emitter (78%). The synergistic approach leads to the realization of high‐performance blue‐emitting PSF‐OLEDs with a maximum external quantum efficiency of 25%, a peak intensity at 465 nm in the electroluminescence spectrum, and a full width at half maximum of 29 nm, achieved by enhancing the outcoupling. In these findings, insight is provided into design strategies for developing PSF systems based on Pt sensitizer and B‐terminal emitter to achieve efficient energy transfer as well as improved EDO.

Adequate method to study the surface passivation effectiveness in HEM multicristallin silicon wafers

In this work we have examined the effectiveness of surface passivation on ascut multicrystalline silicon (mc-Si) wafers using different techniques. The study is based on minority carrier lifetime measurements with quasi steady state photo-conductance, ‘QSSPC’. Effective minority carrier lifetime ()measured values of 12.4, 8.9, 4.9 and 3.1 are obtained respectively with four silicon surface passivation techniques: 1- Shallow phosphorous diffusion emitter (n+p), 2- Iodine-Ethanol (I-E), 3-Hydrofluoric acid (HF) emersion and 4-SiNx layer deposition. These results suggest that the shallow n+p emitter gives the eff close to the bulk lifetime due to the better surface passivation quality. Simulations made with Hornbeck-Haynes model indicate that the improvement can be correlated with the decrease of the surface recombination velocity (SRV) and the increment of bulk lifetime.

Creation of Dual Thermally Activated Delayed-Fluorescence Exciplexes in a Bulk Emitting Layer and Its Interface with an Electron Transport Layer for Promoting the Performance of Thermally Activated Delayed-Fluorescence Organic Light-Emitting Diodes Fabricated by a Solution Process.

An exciplex, which is composed of electron donor and acceptor molecules and formed by intermolecular charge transfer, is an excited-state species that is able to emit light or transfer its energy to a lower-energy emitter. In reported exciplex-based organic light-emitting diodes (OLEDs), their working mechanism is to generate exciplexes either in the bulk emitting layer (bulk exciplex) or at its interface with an electron transport layer (interface exciplex); both types give promising device performance. Here, we propose a novel strategy of creating both types of exciplexes simultaneously (dual exciplexes) for the generation of more exciplexes for better device performance as indicated in the improved photoluminescence quantum yield (PLQY). Impressively, the dual exciplex-based device with blue thermally activated delayed fluorescence (TADF) emitter 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DMAC-TRZ) exhibits a record-high maximum external quantum efficiency (EQEmax) of 26.7% among the solution-processed TADF blue OLEDs. By further doping with the red-emitting phosphor emitter into the EML, the white device also gives a record-high EQEmax of 24.1% among the solution-processed TADF-phosphor hybrid white OLEDs (T-P WOLEDs) with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.34, 0.42), color rendering index of 70, and correlated color temperature of 5198 K. Furthermore, both blue and white devices show an ultralow efficiency roll-off with external quantum efficiencies at a practical brightness value of 1000 cd m-2 (EQE1000) of 25.1 and 23.9%, respectively. This is the first report of employing a dual exciplex-based OLED with excellent device performance.

Spray-coated SiO2/PECVD SiN[formula omitted] stack for the passivation of n[formula omitted] emitter of p-type Si solar cell

Inefficient passivation of phosphorous diffused emitter is one of the limiting factors contributing to lower efficiency in advanced p-type silicon solar cells. Stack of SiO2 and SiNx with the former as an intermediate layer beneath SiNx provides better emitter passivation in comparison to SiNx film alone. Thermal oxide is reported to provide the best passivation, but it is not industrially viable. We demonstrate spray SiO2/SiNx as a viable alternative to thermal SiO2/SiNx stack. A few nanometer thin (∼6.1 nm) spray SiO2 film was first time demonstrated on micrometer sized textured pyramid with full coverage over an entire deposited area. The passivation of symmetrical (n+-p-n+) structure shows iVoc∼660 mV and passivation uniformity over the entire wafer area for both the stacks. Voc∼630 mV is achieved on cells with spray and thermal SiO2 as a passivating layer. Similar front passivation is further verified by overlapping IQE in the shorter wavelength range. Therefore, incorporating SiO2 film deposited via an industrially viable spray-coating process as a passivating layer at the front provides overall cell performance similar to the thermally grown SiO2.

Impact of surface doping profile and passivation layers on surface-related degradation in silicon PERC solar cells

Illuminated solar cells are susceptible to various degradation mechanisms that can act to reduce the total energy yield when deployed. One potentially severe form is an increase in carrier recombination in the surface regions. This effect has been reported at both the undoped rear surface and phosphorous diffused emitter of PERC solar cells. This work investigates the influence of a range of surface conditions on the surface-related degradation (SRD) behaviour in PERC solar cells. It is shown that SRD is strongly affected by the doping profile of phosphorous emitters, the use of thin thermal oxides with SiN x :H dielectric passivation layers, the substrate material, and the configuration of the rear surface passivation. It finds that more lightly doped emitters result in more front side SRD, with its extent increasing with the introduction of the SiO 2 /SiN x :H surface passivation layers. Czochralski silicon (Cz-Si) wafers were observed to be significantly more susceptible to surface degradation than multi-crystalline silicon (mc-Si) wafers, which we attribute to less trapping of hydrogen in the bulk of those substrates. On the rear side of PERC cells, surface degradation was only observed in structures that incorporated the combination of SiO 2 /SiN x :H rear layers. No SRD was observed in the existing Al 2 O 3 /SiN x :H technology used in the industrial PERC cells studied. However, the results presented have implications for future commercial solar cell technologies, which are transitioning towards lightly doped emitters and commonly incorporate thermal oxides for surface passivation. • The introduction of more lightly doped emitters leads to severe SRD, with its extent increasing with the introduction of theSiO 2 . • Cz-Si wafers were observed to be substantially more susceptible to surface degradation than mc-Si wafers. • Rear side SRD was only observed in PERC precursors that incorporated the combination of SiO 2 /SiN x :H rear layers.

Assessing the Potential of Inversion Layer Solar Cells Based on Highly Charged Dielectric Nanolayers

The production and performance of p‐type inversion layer (IL) Si solar cells, manufactured with an ion‐injection technique that produces a highly charged dielectric nanolayer, are investigated. It is demonstrated that the field‐induced electron layer underneath the dielectric can reach a dark sheet resistance of 0.95 kΩ sq−1 on a 1 Ω cm n‐type substrate, lower than any previously reported. In addition, it is shown that the implied open‐circuit voltage of a p‐type IL cell precursor with a highly charged dielectric is equivalent to that of a cell with a phosphorous emitter. In the cell precursor, light‐beam‐induced current measurements are performed, and the uniformity and performance of the IL is demonstrated. Finally, simulations are used to explain the physical characteristics of the interface leading to extremely low sheet resistances, and to assess the efficiency potential of IL cells. IL cells are predicted to reach an efficiency of 24.5%, and 24.8% on 5/10 Ω cm substrates, by replacing the phosphorous emitter with a simpler manufacturing process. This requires a charge density of beyond 2 × 1013 cm−2, as is demonstrated here. Moreover, IL cells perform even better at higher charge densities and when negative charge is optimized at the rear dielectric.

Over 30 000 h Device Lifetime in Deep Blue Organic Light‐Emitting Diodes with y Color Coordinate of 0.086 and Current Efficiency of 37.0 cd A−1

AbstractThe development of highly efficient and long‐life deep blue devices has been an ongoing challenge in the field of organic light‐emitting diodes (OLEDs) because of the short lifetime inherent to highly efficient blue devices. The efficiency and lifetime issues of the deep blue OLEDs are resolved in this work by engineering the device architecture by managing the triplet excitons of the phosphorescence and thermally activated delayed fluorescence (TADF) emitters. The CN‐modified imidazole type Ir emitter and boron‐based TADF emitter with similar emission energy are combined to develop an energy exchanging phosphorescence and TADF (EPHTADF) device. An emission mechanism inducing both forward and backward energy transfer concurrently between the Ir phosphor and TADF emitter shortens the triplet exciton lifetime of the two emitters, which dramatically enhances the device lifetime of the blue devices. Deep blue OLEDs triggering EPHTADF emission ultimately yields device performances including high current efficiency (CE) of 37.0 cd A−1, color‐coordinate corrected CE of 430.9 cd A−1, extrapolated device lifetime of more than 30 000 h, and deep blue color coordinates of (0.122, 0.086). This work demonstrates the potential of EPHTADF devices to serve as the solution to the problematic issues of the blue OLEDs.

A Scanning Spreading Resistance Microscopy Study on a Laser-Doped Selective Phosphorous Emitter

In this work, we present scanning spreading resistance microscopy (SSRM) measurements of a phosphorous emitter formed via tube furnace diffusion and a laser-doped selective emitter (LDSE) processed by additionally doping the tube furnace diffused emitter. The nonlaser-doped emitter is found to be widely homogeneous along the alkaline textured silicon surface. In contrast, the LDSE features large fluctuations in doping depth, almost constant doping concentration along the (laser-modified) surface within a depth of <0.2 μm, and a steep drop of the doping concentration at the p-n-junction. In some parts of the LDSE, the local doping profile is found to decrease stepwise. These findings are new to the photovoltaic community since the named phenomena are not resolved by common characterization methods such as electrochemical capacitance-voltage (ECV) profiling. The limits of ECV profiling are demonstrated by simulating an ECV profile from an SSRM measurement. In this context, we introduce a new method to correct ECV measurements performed on rough surfaces.

Ultrathin Plasma Oxide for Passivation of Phosphorus-Diffused Silicon Solar Cell Emitters

Different passivation layers on phosphorous diffused emitters have been studied. A comparison between silicon nitride (SiNx) single layer at different deposition temperatures, stacks of “outgassing” silicon oxide (that was grown during the moving in/out of the furnace in ambient air during the outgassing process) and an ultrathin SiOx layer formed by plasma oxidation capped with SiNx layers have been investigated. Optimization of plasma enhanced chemical vapor deposition (PECVD) SiNx at different deposition temperatures showed good passivation quality depending on the hydrogen content. Plasma oxidation process by a PECVD tool without utilizing a silicon source in the process gas flow is an obvious choice to form a thin SiOx as it allows the formation of a SiOx/SiNx stack in a sequence of deposition processes in the same inline PECVD tool. Such an ultrathin SiOx layer was found to not only improve the surface passivation after a fast firing process but also to maintain the excellent anti-reflection coating (ARC) property of the SiNx. Low emitter saturation current density J 0 e values of 15 fA/cm2 for planar and 24 fA/cm2 for textured surfaces for an emitter with a sheet resistivity of 161 Ω/ sq has been reached after firing at 850 °C, which is comparable with the outgassing oxide. These stacks gave an improvement of the J 0 e values with a factor of 6–9 for emitters with low surface concentration comparing to single SiNx layer.

EFFECT OF PHOSPHOROUS/BORON DOPING PROFILE DIFFERENCES ON THE PERFORMANCE OF SILICON SOLAR CELLS

This research work was done under title “Effect of phosphorous/boron doping profile differences on the performance of silicon solar cells”. Emitter diffusion either phosphorous or boron is quite challenging in photovoltaic industry. It directly affects the emitter saturation current density and the emitter quantum efficiency of silicon solar cells. Our main objective was to make the comparison of both phosphorous and boron diffused emitters for different peak dopant concentrations in silicon solar cells. It was done by using EDNA 2 simulations. We used different parameters in EDNA 2 and simulated the high efficiency solar cells with boron as back ground and phosphorous as emitter. Then we simulated the solar cells with phosphorous as back ground and boron as emitter. We varied the peak dopant concentration of phosphorous as well boron from 1.6E+17 to 3.9E+20. The best internal quantum efficiency of emitter for phosphorous diffused emitters was 95.1 %, obtained at 1.6E19 (cm-3 ) with an effective emitter depth of 0.675 (µm). However, the best internal quantum efficiency of emitter for boron diffused emitters was 80.6 %, obtained at 3.9E19 (cm-3 ). It has an effective emitter depth of 0.732 (µm) that is greater than obtained from phosphorous diffused emitters. We concluded that the phosphorous diffused emitters have much better performance than boron diffused emitter in silicon solar cells. They have better internal quantum efficiency of emitters at lower peak dopant concentration. They have lower emitter sheet resistance with lower effective emitter depth, as also required during silicon solar cell fabrication.

Superior Efficiency and Low-Efficiency Roll-Off White Organic Light-Emitting Diodes Based on Multiple Exciplexes as Hosts Matched to Phosphor Emitters.

Based on exciplexes as hosts, the monochromatic organic light-emitting diodes (OLEDs) have achieved high power and external quantum efficiencies. However, the high-quality white OLEDs (WOLEDs) with high color rendering index (CRI) have the unsatisfactory efficiencies at high luminance, particularly in terms of power efficiency (PE), resulting in high energy consumption. Here, a new design concept using multiple exciplexes as hosts to match different phosphors has been demonstrated to develop high-performance WOLEDs. It can be seen that the resulting WOLEDs work at a low turn-on voltage of 2.3 V and exhibit the large forward-viewing PE and external quantum efficiency (EQE) of 79 lm W-1 and 22.5%, respectively, without light out-coupling techniques. Significantly, the PE and EQE still remain 48.0 lm W-1 and 21.4% at 1000 cd m-2, showing extremely low efficiency roll-off. The CRI is as high as 81. The keys to success are the selection of the different exciplex hosts matched to different phosphors and the reasonable arrangement of emissive layers, which are beneficial to regulate the exciton distribution and reduce the energy losses.

Direct Hot-Injection Synthesis of Lead Halide Perovskite Nanocubes in Acrylic Monomers for Ultrastable and Bright Nanocrystal-Polymer Composite Films.

In recent years, lead halide perovskite nanocrystals (NCs) have attracted significant attention in both fundamental research and commercial applications because of their excellent optical and optoelectrical properties. However, the protective ligands on the surface of the perovskite NCs could be easily removed after the tedious process of centrifugation, separation, and dispersion, which greatly hampers their stability against light, heat, moisture, and oxygen and limits their practical applications. Here, we report a new post-processing free strategy (i.e., without centrifugation, separation, and dispersion process) of using an ultraviolet (UV)-polymerizable acrylic monomer of lauryl methacrylate as the solvent to synthesize CsPbBr3 NCs, and then adding polyester polyurethane acrylate oligomer, monomer (IBOA), and initiator for direct UV polymerization to fabricate NC-polymer composite films. These films exhibited an improved photoluminescence quantum yield (85-90%) than classic NC films (40-50%), which were processed using octadecene (ODE) as the solvent for NC synthesis and postprocessed for UV polymerization. Significantly, the as-fabricated films by post-processing free strategy exhibited excellent photostability against strong Xe lamp illumination; while the other films using classic methods were quickly photodegraded. Meanwhile, these NC-polymer composite films showed good stability against moisture and heating when aging in water at 50 °C for over 200 h. These films, along with K2SiF6:Mn4+ (KSF) phosphor emitters, were used as downconverters for blue light-emitting diodes in liquid-crystal displays with a wide color gamut of 115% in the International Commission on Illumination (CIE) 1931 color space. This work provides a facile and effective strategy for the preparation of ultrastable and bright color-conversion NC films for the development of the next-generation wide color gamut displays.

Modelling of hydrogen transport in silicon solar cell structures under equilibrium conditions

This paper presents a model for the introduction and redistribution of hydrogen in silicon solar cells at temperatures between 300 and 700 °C based on a second order backwards difference formula evaluated using a single Newton-Raphson iteration. It includes the transport of hydrogen and interactions with impurities such as ionised dopants. The simulations lead to three primary conclusions: (1) hydrogen transport across an n-type emitter is heavily temperature dependent; (2) under equilibrium conditions, hydrogen is largely driven by its charged species, with the switch from a dominance of negatively charged hydrogen (H−) to positively charged hydrogen (H+) within the emitter region critical to significant transport across the junction; and (3) hydrogen transport across n-type emitters is critically dependent upon the doping profile within the emitter, and, in particular, the peak doping concentration. It is also observed that during thermal processes after an initial high temperature step, hydrogen preferentially migrates to the surface of a phosphorous doped emitter, drawing hydrogen out of the p-type bulk. This may play a role in several effects observed during post-firing anneals in relation to the passivation of recombination active defects and even the elimination of hydrogen-related defects in the bulk of silicon solar cells.

Simultaneous measurement of doping concentration and carrier lifetime in silicon using terahertz time-domain transmission

In this work, we present a measurement approach enabling the simultaneous determination of sheet resistance and carrier lifetime in semiconductor samples. It is based on a classic Terahertz (THz) time-domain transmission spectroscopy scheme extended by quasi-steady state optical excitation. The carrier lifetime is determined by contactless THz probing of the increase in sheet conductance associated with quasi-steady-state excitation. Combining a successive etch-back of the surface with repeated THz measurements yields a depth profile of the doping concentration and the carrier lifetime, which is important for the optimization of the emitter of solar cells, for instance. The viability of our approach is demonstrated by investigating a phosphorous doped emitter of a silicon solar cell with the THz approach and comparing the results with electrochemical capacitance voltage measurements.

Top-Emitting White Organic Light-Emitting Diodes Based on Cu as Both Anode and Cathode **Supported by the National Basic Research Program of China under Grant No 2010CB327701, and the National Natural Science Foundation of China under Grant No 61275033.

It is still challenging to obtain broadband emission covering visible light spectrum as much as possible with negligible angular dependence. In this work, we demonstrate a low driving voltage top-emitting white organic light-emitting diode (TEWOLED) based on complementary blue and yellow phosphor emitters with negligible angular dependence. The bottom copper anode with medium reflectance, which is compatible with the standard complementary metal oxide semiconductor (CMOS) technology below 0.13 μm, and the semitransparent multilayer Cs2CO3/Al/Cu cathode as a top electrode, are introduced to realize high-performance TEWOLED. Our TEWOLED achieves high efficiencies of 15.4 cd/A and 12.1 lm/W at a practical brightness of 1000 cd/m2 at low voltage of 4 V.

Impact of structural defect density on gettering of transition metal impurities during phosphorus emitter diffusion in multi-crystalline silicon solar cell processing

The impact of structural defect density on gettering of transition metal impurities during phosphorous emitter diffusion has been investigated using a pair of multi-crystalline silicon (mc-Si) wafers. Chromium (Cr) impurities incorporated during growth were identified by deep level transient spectroscopy (DLTS) and used to evaluate the gettering efficiency. The Cr impurity concentration in the low defect density region of mc-Si wafers was reduced from ~3.5 × 1013 cm−3 to ~1.7 × 1012 cm−3 after phosphorous diffusion gettering (PDG), while for the high defect density region, there is no appreciable variation in the Cr concentration which only changed from ~3.0 to ~2.2 × 1012 cm−3 following PDG. It was concluded that the gettering process is not effective for highly defective regions of mc-Si wafers due to the ineffective impurity release from structural defects during the PDG process. Open image in new window

Carbazole‐endcapped Spiro[fluorene‐9,9′‐xanthene] with Large Steric Hindrance as Hole‐transporting Host for Heavily‐doped and High Performance OLEDs

AbstractIn this work, we designed and synthesized a novel spirocyclic compound functionalized spiro[fluorene‐9,9′‐xanthene] with carbazole group (2‐carbazolyl‐spiro[fluorene‐9,9′‐xanthene], SFX‐Cz) via Friedel‐Crafts and Ullmann reaction, which is expected to own high thermal and morphological stability, and good carrier injection/transporting properties due to the excellent hole transporting characteristics of carbazole and cruciform structure of spiro[fluorene‐9,9′‐xanthene]. The carbazole end‐capped spiro[fluorene‐9,9′‐xanthene] SFX‐Cz based PhOLEDs with FIrpic as phosphor emitter have been researched by varying dopant concentration, which exhibit the maximum EQEs of 8.9%, 7.4%, 9.1%, and 4.7% with the doping increasing from 10% to 50%. The higher performance PhOLEDs are independent on concentration variation from 10% to 30%, which suggests the bulky steric hindrance of SFX‐Cz might be a potential canditate for high performance and inexpensive device with simplified process.

Extremely high chromatic-stability white organic light-emitting device with symmetrical cascade emissive layer

We have employed four adequate complementary phosphor emitters (blue, green, yellow, and red) and two host and transport materials (CBP: 4,4′-bis(carbazol-9-yl)biphenyl; TPBi: 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) to configure a symmetrical cascade emissive layer white organic light-emitting device (WOLED), in which four emitters are in turn incorporated in CBP and TPBi from high to low energy level from CBP/TPBi interface. The symmetrical cascade emissive layer WOLED shows extremely high chromatic-stability with a slight CIE coordinates shift at wide range of driving voltage. As the voltage increases from 5V to 9V, the symmetrical cascade emissive layer WOLED maintains CIE coordinates of (0.384, 0.467)–(0.387, 0.469) and high color rendering index (CRI) of 85–86 with ideal correlated color temperature (CCT) of 4407–4292K. Furthermore, this WOLED also exhibits a peak current efficiency of 43.6cd/A and a maximum power efficiency of 31.1lm/W, which are much higher (by 1.43 and 1.50 times) than those of the reference device with four emitters only being doped in single CBP host. The improvement of color stability is due to the fact that symmetrical cascade emissive layer suppresses the shift of carrier recombination zone as the voltage increases; the improvement of efficiency is attributed to the effective utilization of excitons.

Arylsilanes and siloxanes as optoelectronic materials for organic light-emitting diodes (OLEDs)

Arylsilanes and siloxanes have been extensively studied as components of OLEDs. In this review, we summarize the recent advances in the utilization of arylsilanes and siloxanes as fluorophore emitters, hosts for phosphor emitters, hole and exciton blocking materials, and as electron and hole transporting materials.

Contacting Moderately Doped Phosphorous Emitters of Silicon Solar Cells With Dopant Segregation During Nickel Silicidation

Emitter performance is crucial for the efficiency of solar cells. A further increase of efficiency requires reducing recombination losses while keeping parasitic resistances and shadowing at a minimum. In silicon solar cells, recombination can be lowered by decreasing the emitter doping concentration; however, this comes at the cost of increasing contact and sheet resistances. Dopant segregation during nickel silicidation resolves this tradeoff since it allows ohmic contact formation to emitters with almost arbitrary doping profile and concentration. Here, we elaborate on using dopant segregation during silicidation and demonstrate contact formation, as well as a substantial performance improvement of silicon solar cells exhibiting a lowly doped emitter with a peak doping concentration of 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Furthermore, we show that the small achievable contact resistances in principle allow a strong reduction of the contact area. In turn, this enables lowering the shadowing while, at the same time, decreasing the sheet resistance due to a larger number of front contacts that can be placed close to each other. Using PC1D simulations, we study the solar cell performance as a function of the emitter dopant concentration estimating the achievable efficiency increase when employing dopant segregation.