Barrier For Hole Transport Research Articles

Enhancing the emissive film quality: a new role of TADF materials for high-performance blue perovskite light-emitting diodes

Thermally activated delayed fluorescence (TADF) materials are widely used in the field of organic light-emitting diodes (OLEDs) because they can capture both singlet and triplet excitons for light emission. However, only scare attention has been paid to the application of TADF materials in perovskite LEDs (PeLEDs) and the understanding of effects of TADF materials in PeLEDs is limited. In this study, a new role of TADF materials for achieving high-quality perovskite films to enhance the performance of PeLEDs is emphasized. TADF materials are introduced into quasi-2D blue PeLEDs to assist in the crystallization of perovskites during film annealing and ensure the formation of high-quality films with reduced defects, enhancing device performance. Additionally, a step-like hole transport layer has been constructed to reduce the hole transport barrier, which can further enhance the performance of PeLEDs. The resultant blue PeLEDs exhibits an external quantum efficiency of 5.44%, which is 12.7-fold higher than that of the control device. Furthermore, a turn-on voltage of 2.6 V is achieved, which is the lowest for TADF-based blue PeLEDs. The findings may not only unlock a new role of TADF materials in blue PeLEDs, but also provide an alternative pathway to achieve high-performance PeLEDs.

Construction of Efficient Cs2AgBiBr6 Perovskite Solar Cells by Enhancing Hole‐Selective Contact with Deep‐Level Dopant‐Free Hole Transport Material

AbstractThe mismatched energy level alignment at the hole transport interface is recognized to be a prominent limitation for the Cs2AgBiBr6‐based perovskite solar cell (PSC) to achieve high power conversion efficiency (PCE) but has not been well investigated yet. In order to solve this problem to some extent, it is proposed to balance the energy offset at the Cs2AgBiBr6 and hole transport material (HTM) interface to reduce the hole transport barriers, and a novel HTM TPTI‐TPA2F with deep level is designed to implement this strategy. The research demonstrates that, on the one hand, the planar π‐conjugation and the presence of multiple heteroatoms on TPTI‐TPA2F facilitate the formation of well‐oriented film and surface defect passivation; on the other hand, the higher film ionization potential of TPTI‐TPA2F effectively balances the energy barrier for hole transport. As a result, improved hole‐selective contact is achieved with TPTI‐TPA2F as HTM, and the interfacial energy loss is suppressed. Correspondingly, the optimized Cs2AgBiBr6 PSCs using the TPTI‐TPA2F HTM without doped feature an excellent PCE of 4.05% and a high open circuit voltage of 1.15 V, with much improved long‐term humidity and thermal stability. This work provides an attractive strategy for developing efficient Cs2AgBiBr6 PSCs.

Surface p-type band bending and energy level alignment minimizes voltage loss in perovskite solar cells

Due to the significant energy level mismatch and contact energy loss between the perovskite absorber layer and p-type hole-transporting layer (HTL), there exists a large hole transport barrier between the perovskite absorber layer and HTL, which hinders hole transport and leads to lower open circuit voltage (VOC) in perovskite devices. Therefore, the surface contact process between the perovskite film and the hole-transporting layer becomes particularly important. Here, we doped cesium silver bismuth bromide (Cs2AgBiBr6) quantum dots (QDs) into ethyl acetate (EA) as an anti-solvent to achieve the formation of a bulk heterojunction structure with quantum dot solution on the surface of the MAPbI3 perovskite film. The perovskite film exhibits appropriate band edge bending and forms a p-type semiconductor. This facilitates the directed transport of photo-induced charge carriers to the hole-transporting layer, reducing carrier recombination losses and enhancing the collection efficiency of holes by the HTL. Through characterization experiments, we have found that this method significantly improves the VOC and photovoltaic conversion efficiency (PCE) of perovskite solar cells. The perovskite solar cells fabricated using this method show a better PCE with a VOC of 1.06 V.

Minimizing the buried interfacial energy loss using a fluorine-substituted small molecule for 25.92%-efficiency and stable inverted perovskite solar cells

Tetrafluorosuccinic acid was introduced into the buried interface to stabilize FA cations, mediate crystal growth of perovskite and reduce the hole-transport barrier, delivering a record efficiency of 25.92% for RbCsFAMA-based perovskite solar cells.

D 6 h Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

Efficient Pure Blue Light-Emitting Diodes Based on CsPbBr3 Quantum-Confined Nanoplates

Exploitation of next-generation blue light-emitting diodes (LEDs) is the foundation of the revolution in lighting and display devices. Development of high-performance blue perovskite LEDs is still challenging. Herein, 4-aminobenzenesulfonic acid (SA) is introduced to passivate blue CsPbBr3 nanoplates (NPLs), reducing the ionic migration via a more stable Pb2+-SO3-- formation, and the trap state density of films shows a 50% reduction. The inevitable Br- vacancy defects after the multistep washing process can be suppressed by a suitable MABr treatment, which can boost the external quantum efficiency (EQE) performance. It should be noted that the coverage of NPL films is another key factor to realize reproducible pure blue electroluminescence (EL). Therefore, we proposed an alternate droplet/spin coating method to improve the coverage and thickness of NPL layer to prevent hole transport layer emission and increase the reproducibility of LED performance and spectra. Furthermore, we designed hole transport layers to decrease the hole transport barrier and improve the energy-level alignment. According to SA passivation, MABr treatment, alternate droplet/spin coating method, and device structure optimization, a CsPbBr3 NPL-based pure blue (0.138, 0.046) LED with 3.18% maximum EQE can be achieved, and the half-lifetime of EL can be enhanced 1.71 times as compared to that of the counterpart LED without SA. Both performance and stability of pure blue NPL LEDs can be greatly improved via ligand passivation, alternate droplet/spin coating method, and device structure optimization, which is a trend to promote the development of pure blue perovskite LEDs in future.

Metastable Dion-Jacobson 2D structure enables efficient and stable perovskite solar cells.

The performance of three-dimensional (3D) organic-inorganic halide perovskite solar cells (PSCs) can be enhanced through surface treatment with 2D layered perovskites that have efficient charge transport. We maximized hole transport across the layers of a metastable Dion-Jacobson (DJ) 2D perovskite that tuned the orientational arrangements of asymmetric bulky organic molecules. The reduced energy barrier for hole transport increased out-of-plane transport rates by a factor of 4 to 5, and the power conversion efficiency (PCE) for the 2D PSC was 4.9%. With the metastable DJ 2D surface layer, the PCE of three common 3D PSCs was enhanced by approximately 12 to 16% and could reach approximately 24.7%. For a triple-cation–mixed-halide PSC, 90% of the initial PCE was retained after 1000 hours of 1-sun operation at ~40°C in nitrogen.

RF magnetron sputtered NiO&amp;lt;sub&amp;gt;&amp;lt;italic&amp;gt;x&amp;lt;/italic&amp;gt;&amp;lt;/sub&amp;gt; and NiO&amp;lt;sub&amp;gt;&amp;lt;italic&amp;gt;x&amp;lt;/italic&amp;gt;&amp;lt;/sub&amp;gt;/c-Si single-side heterojunction solar cells

<p indent=0mm>NiO_{<italic>x</italic>} is a p-type semiconductor with wide-band gap <sc>(3.6–4.0 eV),</sc> and the energy band structure at NiO_{<italic>x</italic>}/c-Si(n) interface is suitable for c-Si(n) heterojunction solar cell. On the one hand, the big conduction band offset forms a reflection barrier of electron that reduces the interface electron concentration and interface recombination. On the other hand, the valance band offset will change with the deposition conditions, which lower the hole transport barrier and make the hole transport smoothly. Therefore, NiO_{<italic>x</italic>} is a promising hole-selective contact layer for c-Si(n) heterojunction solar cell. In this work, in order to simplify the study, we fabricate single-side heterojunction solar cell with Al-grid/ITO/NiO_{<italic>x</italic>}/SiO_{<italic>x</italic>}/c-Si(n)/SiO_{<italic>x</italic>}/Al-electrode structure. The n-type c-Si(100) wafers with resistivity of <sc>1–10 Ω cm</sc> and thickness of <sc>200 μm</sc> were firstly dipped in KOH solution (25wt%) at 80°C for <sc>4 min</sc> to remove the surface sawing damage, then standardized RCA1 procedure and DHF (6wt%) dip were adopted to remove the contaminants and native oxide presented on the wafer surface. The SiO_{<italic>x</italic>} layer was grown in 5wt% H₂O₂ at 80°C for <sc>20 min.</sc> Afterward, a NiO_{<italic>x</italic>} thin film with thickness of <sc>10 nm</sc> was deposited on the wafer front side using RF magnetron sputtering, and a <sc>100 nm</sc> thick ITO layer was deposited on NiO_{<italic>x</italic>} by DC magnetron sputtering. Then Al-grid on the front and Al-electrode on the back were deposited by electron-beam evaporation. Finally, completed NiO_{<italic>x</italic>}/c-Si(n) single-side heterojunction solar cells were characterized by light/dark <italic>J</italic>-<italic>V</italic> (SAN EI XEC 500M2 solar simulator, KEYTHLEY 2400 source-meter). We investigate the optical, electronical properties and energy band of NiO_{<italic>x</italic>} thin films by changing the sputtering conditions, analyze the carrier transport mechanisms and the interface recombination mechanisms of NiO_{<italic>x</italic>}/c-Si heterojunction. And we find that the valance band offset is the key factor that affects cell performance. The increase of the valance band offset leads to the increase of the series resistance (<italic>R</italic>_s) of the cell, thus reducing the fill factor (FF) and power conversion efficiency (PCE) of the cell (cell Sample B, E and A). When the valance band offset is high and almost the same, the lower the resistivity of NiO_{<italic>x</italic>} thin film is, the lower the series resistance (<italic>R</italic>_s) of the cell becomes, which contributes to the higher FF and the higher PCE of the cell. This is because the lower resistivity of NiO_{<italic>x</italic>} thin film narrows the width of the blocking barrier of the hole and increases the tunneling current (cell Sample A and B). In addition, the experiment and the simulation results (AFORS-HET) show that there are two ways to enhance the cell performance. One is to reduce the valence band offset and interface defects of NiO_{<italic>x</italic>}/c-Si heterojunction so as to lower the interface recombination. The other one is to increase the doping density in NiO_{<italic>x</italic>} that increase the built-in electric field. Therefore, the passivation of NiO_{<italic>x</italic>}/c-Si(n) interface, the improvement of acceptor concentration of NiO_{<italic>x</italic>} emitter, the optimization of back surface field and ITO/NiO_{<italic>x</italic>} contact are the main directions for further research to achieve high efficiency NiO_{<italic>x</italic>}/c-Si heterojunction solar cells.

Degradation study of carrier selective contact silicon solar cells with ageing: Role of silicon surface morphology

Ageing effect on the performance of Ag/ITO/MoOx/n-Si/LiFx/Al carrier selective contact (CSC) silicon solar cells has been investigated based on silicon surface morphology (planar, different pyramid sizes, and chemical polishing of pyramids). The cells with small silicon pyramids (~2 µm) have shown better stability with time than the medium/large pyramids (~5/~8 µm). The chemical polishing of pyramid peaks and valleys has further reduced the cells ageing effect due to minimization of the microstructural stress (tensile in the valleys and compressive at the peaks) at the MoOx/n-Si interface, which has been verified indirectly with cells fabricated on a planar surface. The cell’s performance degradation based on morphology points out the instability of the MoOx layer and Schottky barrier reduction, which results in hole-transport hindrance at the MoOx/n-Si junction with the S-shape in J-V graphs under illumination. The ageing effect on device performance is further investigated using the Sentaurus TCAD simulations with the MoOx layer work function variation, and the study indicates the band bending reduction (minimal carrier inversion) and hole transport barrier at the junction region.

Improved performance of lead-tin mixed perovskite solar cells with PEDOT:PSS treated by hydroquinone

Low bandgap lead-tin (Pb-Sn) hybrid perovskite solar cells (PVSCs) have gained a great deal of attentions due to their wide optical absorption range and environmental friendliness. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is widely used as a hole transport layer for PVSCs. However, the metallic property of PEDOT:PSS causes a barrier at the interface between it and the active layer, thereby hindering the transport of photogenerated carriers. In this paper, in order to eliminate the influence of the interfacial barrier, the PEDOT:PSS surface was treated by hydroquinone (HQ), which lowers the hole transport barrier at the interface, and consequently reduces the interfacial resistance as well. The leakage current in the device with the HQ-treated PEDOT:PSS is significantly reduced, and the surface modification improves the interfacial contact. Compared with the Pb-Sn hybrid PVSCs with the PEDOT:PSS hole transport layer, the power conversion efficiency of PVSCs with the HQ-PEDOT:PSS hole transport layer is improved by 5.7%.

Predictive Modeling of CuInSe2 Nanocrystal Photovoltaics: The Importance of Band Alignment and Carrier Diffusion

Nanocrystal inks have been used to make printed photovoltaic devices (PVs) with reasonably high efficiencies; however, little is actually known about the material properties that limit the performance of these devices. Here, we model the output characteristics of PVs with CuInSe2 nanocrystal absorber layers using the Solar Cell Capacitance Simulator (SCAPS) software package and obtain the thickness-limited response and typical current–voltage behavior, power conversion efficiency (PCE), and external quantum efficiency (EQE) of experimentally fabricated PVs. The device behavior is accurately modeled using a low carrier mobility of 5 × 10–4 cm2 V–1 s–1 and measured optical properties for the CuInSe2 nanocrystal films. The simulations reveal that a reduction in the energy barrier for hole transport at the back contact and increased mobility and lifetime of charge carriers in the CuInSe2 nanocrystal layer could improve device performance. Furthermore, this system is qualitatively different than the well-studi...

Treating the Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Surface with Hydroquinone Enhances the Performance of Polymer Solar Cells.

The introduction of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a standard hole transport layer greatly increased the efficiency of early organic solar cells. However, because PEDOT:PSS has a metallic property, it can still form a barrier by means of metal-semiconductor contact at its interface with the photoactive layer. In this study, we modified the PEDOT:PSS surface with hydroquinone (HQ) to remove that barrier. HQ treatment of the PEDOT:PSS surface lowered the hole transport barrier at the interface between the PEDOT:PSS and the active layer. In addition, because of the secondary doping effect of HQ, the sheet resistance of the PEDOT:PSS surface decreased by almost 2 orders of magnitude. As a result, the device fabricated with the HQ-modified PEDOT:PSS showed a 28% increase in efficiency compared to the device without HQ treatment. Modifying the PEDOT:PSS surface with HQ solution is an easy way to effectively boost the performance of polymer solar cells.

Achieving High Open‐Circuit Voltage for p‐i‐n Perovskite Solar Cells Via Anode Contact Engineering

With photocurrents in perovskite solar cells close to their practical limit, it is imperative to improve their open‐circuit voltage to go beyond a loss‐in‐potential less than 100 mV. However, state‐of‐the‐art p‐i‐n perovskite solar cells are reported with a Voc of around 1.1–1.5 V, limiting their efficiency improvement. Herein, the authors demonstrate that the Voc of p‐i‐n perovskite solar cells can be successfully improved via anode contact engineering. First of all, by introducing a partially oxidized nickel layer, the authors are able to remove the potential barrier for hole transport and enhance the crystallinity of the hole transporting layer, both of which are believed to contribute to the Voc and FF improvement. Furthermore, by separating the inorganic NiMgOx hole transporting layer from the perovskite absorbing layer with a poly(4‐vinylpyridine) (PVP) insulating layer, the interfacial recombination could be effectively suppressed, the Voc climbs to an impressive value of 1.15 V along with a power conversion efficiency of 19.3%. Finally, a substrate‐type perovskite solar cell is fabricated with an extremely high Voc of 1.18 V, representing a very low voltage deficit in the p‐i‐n perovskite solar cells. Our works provide an avenue for further reducing the loss‐in‐potential of perovskite solar cells.

Band-Tail Transport of CuSCN: Origin of Hole Extraction Enhancement in Organic Photovoltaics.

Copper thiocyanate (CuSCN) is known as a promising hole transport layer in organic photovoltaics (OPVs) due to its good hole conduction and exciton blocking abilities with high transparency. Despite its successful device applications, the origin of its hole extraction enhancement in OPVs has not yet been understood. Here, we investigated the electronic structure of CuSCN and the energy level alignment at the poly(3-hexylthiophene-2,5-diyl) (P3HT)/CuSCN/ITO interfaces using ultraviolet photoelectron spectroscopy. The band-tail states of CuSCN close to the Fermi level (EF) were observed at 0.25 eV below the EF, leading to good hole transport. The CuSCN interlayer significantly reduces the hole transport barrier between ITO and P3HT due to its high work function and band-tail states. The barrier reduction leads to enhanced current density-voltage characteristics of hole-dominated devices. These results provide the origin of hole-extraction enhancement by CuSCN and insights for further application.

Comparative performance analysis of InGaN/GaN multi-quantum-well light-emitting diodes with p- and n-type step-doped barriers

The performance of InGaN/GaN light-emitting diodes (LEDs) with multiple-quantum-well barriers formed from alternating p- and undoped regions is compared with that of reference devices having similar epilayer structure but with barriers formed from alternating n- and undoped regions. Simulations verify that p-type step-doping in the quantum barriers is more effective in reducing the polarization-induced electric field and lowering the energy barrier for hole transport as well as increasing the barrier height of the conduction band to confine electrons, thereby enhancing the radiative recombination rate compared with n-type step doping in the quantum barriers. This profile also increments hole injection and provides a more uniform carrier distribution across the multiple quantum wells. According to the simulation results, when using the alternating stepwise doping profile in the barrier regions in the proposed structure, the internal quantum efficiency is remarkably improved, offering dual advantages of a homogeneous hole distribution due to the undoped region and a reduced valence-band barrier height due to the p-doping.

Adsorption, film growth, and electronic structures of 2,7-dioctyl[1]benzothieno-[3,2-b][1]benzothiophene (C8-BTBT) on Cu (100)

Using ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM), and grazing X-ray diffraction measurement(GIXRD), we systematically investigate the correlations of interface energy level structure, film growth and the molecular orientation of 2, 7-dioctyl[1]benzothieno-[3, 2-b][1]benzothiophene (C8-BTBT) on Cu(100). We find that the adsorption of the first layer of C8-BTBT molecules on Cu(100) is a stable physical one, and there is no chemical shift of the S 2p peaks of XPS and the ratio of the output of C to that of S is the same as the stoichiometric value of the molecular C8-BTBT. The heights of the steps of the upper layers of C8-BTBT in the AFM images are ～ 30 , close to the length of the molecular long c-axis, indicating the standing-up configuration of the upper molecules. AFM image shows that the upper molecules tend to grow into islands while the bottom molecules tend to grow into layer, suggesting an Stranski-Krastanov growth mode of multilayer C8-BTBT on Cu(100). The GIXRD shows an out-of-plane period of 30.21 , which consistently proves the standing-up configuration of the outer molecule layer. There is an electric dipole of 0.41 eV at the very interface pointing from the substrate copper to C8-BTBT, which will reduce the barrier for electron transport and increase the barrier for hole transport from Cu to C8-BTBT. The vacuum level (Evac) starts to bend downward after 16 deposition, and with the increase of the thickness of the film, a total downward shift of 0.42 eV is observed. The downward shift is ascribed to the changing of molecular orientation from lying down before 16 to standing up after 16 , which establishes an outward-pointing layer of C-H bonds and accordingly forms a dipole layer depressing the surface barrier. The shape and leading edge of the hightest occupied molecular orbit (HOMO) also change with the increase of film thickness. These changes are due to the anisotropy of electron ionization from molecular orbit. The total downward shift of the HOMO is about 0.63 eV. The downward bending of 0.42 eV for Evac and 0.63 eV for HOMO with increasing film thickness lead to a slightly decreasing ionization potential (IP) about 0.1 eV before 32 and then an increasing IP about 0.31 eV, which finally results in a total increase of 0.21 eV for IP. The bending electronic structures facilitate electron transport from interface to surface and hole transport from surface to interface. Our Investigation provides valuable information for relevant device design.

Unlocking the potential of p-doped hole transport layers in inverted organic light emitting diodes

The MoO3 doped N,N′-bis-(1-naphthyl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB:MoO3 in 2:1 mass ratio) and 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3 in 2:1 mass ratio) as p-doped hole transport layers have been used in inverted organic light emitting diodes (IOLEDs). Compared to the NPB/20nm NPB:MoO3 structure, the NPB/10nm CBP:MoO3/10nm NPB:MoO3 structure showed increased device performance, mostly because the hole transport barrier from CBP:MoO3 to NPB was smaller than that from NPB:MoO3 to NPB; it also presented improved device performance than the NPB/20nm CBP:MoO3 structure, ascribed to the higher conductivity of NPB:MoO3 than that of CBP:MoO3. We provide a manageable way to unlock the merits of p-doped hole transport layers for markedly increasing the performance of IOLEDs.

Interfacial insight in multi-junction metal oxide photoanodes for water-splitting applications

Photoelectrochemical (PEC) properties of nanostructured hematite (Fe2O3) thin films prepared using plasma-enhanced chemical vapor deposition (PE-CVD) were investigated against the influence of processing parameters and post-synthesis heat-treatment procedures. Annealing at high temperatures (>500°C) was found to substantially affect the micro-structure (grain growth and densification) and electronic (interdiffusion at the film/substrate interface) concomitantly manifested in an enhancement in the PEC behavior. The Sn impurity level in hematite films was found to increase with the annealing temperature with highest values achieved in samples heat-treated at 750°C, due to the interdiffusion and substitution of Sn(IV) species at Fe(III) sites. Sn:Fe2O3 films exhibited significantly high photocurrent density of 1.33mAcm−2 at the water oxidation level of 1.23V vs. RHE. The diffusion of Sn ions into iron oxide lattice altered the electronic properties of hematite films due to electron–donor behavior of the dopants that was verified by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS) analyses. Deposition of a thin overlayer of TiO2 (10nm) on hematite films by atomic layer deposition (ALD) was found to further improve the photocurrent density to 1.8mAcm−2 at 1.23V vs. RHE. Ab-initio calculations on the effect of substitutional Sn(IV) dopants in the Fe2O3 lattice on the electronic structure and the band alignment between hematite and the TiO2 over layer revealed that Sn-dopants led to the generation of localized Fe(II) centers augmenting the n-type behavior of hematite. No effect of the Sn-doping on the electrostatic potential was found on a macroscopic scale. However, the charge transfer from the Sn-doping to the Fe(II) centers would cause high electric fields on the nanometer scale and might hence play an important role in the efficient separation of electron and holes. The simulations showed that the hematite band edges are enclosed by the TiO2 band edges and therefore electron depletion at the surface–liquid interface is enhanced. This might lead to reduced recombination rates near the surface and consequently to increased photocurrents, since the Fe2O3/TiO2 interface constitutes a barrier for hole transport.

Iron pyrite nanocrystal film serves as a copper-free back contact for polycrystalline CdTe thin film solar cells

We report the application of thin film nanocrystalline (NC) FeS2 as the copper-free back contact for CdTe solar cells. The FeS2-NC layer is prepared from solution directly on the CdTe surface using drop-casting coupled with a hydrazine treatment at ambient temperature and pressure, and requires no thermal treatment. Copper-free solar cells based on the CdS/CdTe/FeS2-NC/Au architecture exhibit device efficiencies >90% that of a standard Cu/Au back contact devices. The FeS2-NC back contact solar cells show good thermal stability under initial tests. Devices prepared with untreated FeS2-NC back contacts display a strong “S-kink” behavior which we correlate with a high hole-transport barrier arising from inter-NC organic surfactant molecules.

A performance assessment of type-II interband In0.5Ga0.5Sb QD photodetectors

Self-assembled quantum-dot (QD) structures with type-II band alignment to the surrounding matrix material have been proposed as a III/V material approach to realize small-bandgap device structures suitable for photon detection and imaging in the long-wavelength infrared (LWIR) band. Here, we analyze the photoresponse of In0.5Ga0.5Sb/InAs QD photodiodes and estimate the system performance of type-II QD –based photodetectors. A review of alternative design approaches is presented and the choice of matrix material is discussed in terms of band alignment and its effect on the photoresponse.Photodiodes were fabricated consisting of 10 layers of In0.5Ga0.5Sb QDs grown on InAs (001) substrates with metal–organic vapor-phase epitaxy (MOVPE). The photoresponse and dark current were measured in single pixel devices as a function of temperature in the range 20–230K. The quantum efficiency shows an Arrhenius type behavior, which is attributed to hole trapping. This severely limits the detector performance at typical LWIR sensor operating temperatures (60–120K). A device design with the matrix material InAs0.6Sb0.4 is proposed as a mean to improve the performance by reducing the barrier for hole transport. This can potentially allow type-II InGaSb QDs to be a competitive sensor material for LWIR detection.