Built-in Field Research Articles

Piezotronic-enhanced photocatalytic performance of heterostructured BaTiO3/SrTiO3 nanofibers

The piezoelectric effect can effectively modulate the energy band structure of the optoelectronic semiconductor and the transport behavior of carriers. Here, we propose a BaTiO 3 /SrTiO 3 nanocomposite, and effectively enhance its photocatalytic performance through piezoelectric effect. The heterostructured BaTiO 3 /SrTiO 3 nanofibers were prepared by electrospinning, and they were polarized by a high-voltage electric field. Under the co-excitation of ultrasonic and UV irradiation, the BaTiO 3 /SrTiO 3 nanofibers presented excellent degradation ability of pollutants in water. The BaTiO 3 /SrTiO 3 nanofibers can degrade Rhodamine B (RhB) dye by ~97.4% within 30 min under the combined action of ultrasonic and ultraviolet irradiation, which was 2.2 times that of pure SrTiO 3 nanofibers. The piezoelectric effect provides a built-in polarization field to improve the separation efficiency of photo-generated carriers. Moreover, DFT calculation results showed that piezoelectric potential can reduce the band gap width of the SrTiO 3 . This article provides a promising strategy for improving photocatalytic performance of nanocomposites through the use of mechanical energy. Here, we propose a heterostructured BaTiO 3 /SrTiO 3 nanocomposites that present enhanced photocatalytic performance through a piezotronic effect. The piezopotential generated in the BaTiO 3 /SrTiO 3 nanofibers under ultrasonic significantly improves the photocatalytic performance of the catalysts. • Heterostructured BaTiO 3 /SrTiO 3 nanofibers were prepared by electrospinning technique for piezo-photocatalysis. • Photocatalytic performance of BaTiO 3 /SrTiO 3 nanofibers were significantly improved through piezotronic effect. • Density functional theory (DFT) calculations prove that the band gap of SrTiO 3 can be modulated by an electric field.

Enhanced Catalytic Mechanism of Twin-Structured BiVO4.

Twin engineering is an efficient strategy to improve the photocatalytic activity of semiconductors (e.g., BiVO4). A systematic study that combines theory and experiments is conducted to reveal the underlying enhanced catalytic mechanism of twin-structured BiVO4. The key characteristic of twinned structures is the partial strain introduced by twin boundaries. Lattice distortion introduced by the twin boundaries leads to charge redistribution and built-in electronic fields between the twin boundaries and the bulk. The generated homojunctions possess a staggered band alignment structure, and their band offsets are increased by the Fermi-level pinning effect. The series of homojunctions in twinned structures is beneficial for facilitating charge separation. Additionally, lattice distortion around twin boundaries leads to the broken geometric symmetry of metal-oxygen polyhedrons in twinned crystals. The adsorption energies of adsorbates decrease significantly, resulting in reduction of the overpotential. The reduced overpotential favors acceleration of the oxygen evolution reaction on twinned structures.

Modelling the photoemission characteristics of parallel aligned (Al)GaN nanowall arrays assisted by built-in/external field

The photoemission and electron collection properties of nanostructure photoemitter based on parallel aligned (Al)GaN nanowall arrays are investigated. In general, the photoelectric conversion efficiency of intrinsic GaN NWAs exhibit a significant improvement compared with planar photoemitter. Assisted by the built-in field induced by gradient decreasing Al component along axial direction of the nanowall, the proportion of emitting photoelectrons on each surface of a nanowall is redistributed and the collected photocurrent is obviously enhanced yet with a negative effect against quantum efficiency and emitted photocurrent. External field incorporation can tune the electron emitting path and improve the collection efficiency, but accompanied with a further decline in emitting photocurrent and quantum efficiency. For a certain configuration with nanowall height of 1 µm and spacing length of 1 µm, the optimum field intensity for emitting and collected photocurrent are respectively 0.3 and 0.5 V/µm. The alteration of photocurrent varied with field intensity dominated by the photoelectrons from the top surface and irradiated side face of the nanowall.

Construction of Schottky contact by modification with Pt particles to enhance the performance of ultra-long V2O5 nanobelt photodetectors

Schottky-contacted nanosensors have attracted extensive attention due to their high sensitivity and fast response time. In this article, we proved that the construction of Schottky contact by Pt nanoparticles (NPs) decoration can effectively improve the performance of V2O5 nanobelts photodetectors. After modified by Pt NPs, the photocurrent of V2O5 nanobelts is increased by more than two orders of magnitude, and the photoresponse speed is improved by at least three orders of magnitude. Detailed studies have shown that the performance enhancement is attributed to the formation of the Schottky contact at the electrode-semiconductor interface due to the decrease of surface gas adsorption and the increase of V2O5 work function after Pt NPs modification. The strong built-in field in the Schottky barrier region will quickly separate photogenerated carriers, thereby reducing the electron-hole recombination rate, resulting in the fast response time and an increase in the free carrier density. Moreover, it is found that this enhancement effect can be regulated by controlling the pressure to modulating the Schottky barrier height at the interface. Overall, the Pt NPs-modified V2O5 nanobelts photodetector exhibits a broad response spectrum (visible to near infrared), fast rise/fall response time (less than 6.12/6.15 ms), high responsivity (5.6 A/W), and high specific detectivity (6.9 × 108 Jones). This study demonstrates the feasibility of building a Schottky barrier to enhance the photodetection performance, which provides a general and effective strategy towards the construction and its practical application of supersensitive and fast-response nanosensors.

A self-powered solar-blind photodetector based on polyaniline/α-Ga2O3 p–n heterojunction

In this work, we demonstrated the self-powered solar-blind photodetector based on a polyaniline/α-Ga2O3 hybrid heterojunction. The resultant device exhibited distinct self-power characteristics with a peak photoresponsivity (R) of 8.2 mA/W, a UVC (UV light of wavelength range at 200–280 nm)/UVA (UV light of wavelength range at 320–400 nm) rejection ratio (R220 nm/R400 nm) of 2.97 × 104, and a response decay time (τdec) of 176 μs at zero bias. With an elevated bias to 5 V, the dark current remained in an ultralow level of 0.21 pA, while the rejection ratio and τdec were improved to be 7.13 × 104 and 153 μs, respectively, together with the corresponding external quantum efficiency of 38.4% and a detectivity of 6.63 × 1013 Jones. Thanks to the dual functions of bandpass transmission in the deep-ultraviolet spectral region and the hole spreading transport of the polyaniline layer, the responsivity to the visible light is suppressed with the negligible internal photoemission effect, thus leading to the improved rejection ratio. Furthermore, weak interface interactions in such polyaniline/α-Ga2O3 organic–inorganic hybrid systems avoid the introduction of interfacial trapping centers by lattice mismatch and the stabilization of negatively charged anions (O2−) by (−NH2)-+species in polyaniline deactivate oxygen vacancies at the α-Ga2O3 surface, both of which lead to the negligible persistent photoconductivity effect. As a result, in the aid of the interfacial built-in field, the constructed hybrid heterojunction exhibited a self-powered detecting characteristic and a fast response speed. These findings verify the feasibility of delivering high performance photodetectors by implementing the inorganic/organic hybrid bipolar device design to overcome the difficulty in p-type Ga2O3.

A comparative study on the band diagrams and efficiencies of silicon and perovskite solar cells using wxAMPS and AMPS-1D

wxAMPS is a popular software widely used in simulating state-of-art solar cells; however, the official documentation for it does not exist. Herein, we compiled information from literature and compared the wxAMPS simulation results with the software it was developed from, AMPS-1D. We first delineated three new tunneling models introduced in wxAMPS: trap-assisted, intra-band, and band-to-band, and highlighted its salient features of the GUI, file I/O, data visualization, and numerical methods. Conventional c-Si solar cells were then used to elucidate the origin of the photovoltaic response. It was evident that devices operating on the built-in electrostatic field achieved a higher efficiency (3%) than those on the effective field (0.05%) and Dember effect (almost zero). High-efficiency Si solar cells in p-n and p-i-n junctions were further studied. It was found both hole and electron transport layers play critical roles in optimizing the power conversion efficiencies. An occasional convergence issue was observed in calculating charge carrier densities in p-i-n device, in which case the slightly deviated JV characteristics can be mainly attributed to the tunneling models. When running the batch simulation on homojunction perovskite solar cells, the voltage bias step size was tuned smaller than 0.01 V in wxAMPS to produce data of higher accuracy than AMPS-1D. Among all the performance parameters, the fill factor was found to be most sensitive to the voltage bias step.

Unraveling the Photophysics of Liquid-Phase Exfoliated Two-Dimensional ReS2 Nanoflakes

Few-layered transition metal dichalcogenides (TMDs) are increasingly popular materials for optoelectronics and catalysis. Amongst the various types of TMDs available today, rhenium-chalcogenides (ReX2) stand out due to their remarkable electronic structure, such as the occurrence of anisotropic excitons and potential direct bandgap behavior throughout multi-layered stacks. In this letter, we have analyzed the nature and dynamics of charge carriers in highly crystalline liquid-phase exfoliated ReS2, using a unique combination of optical pump-THz probe and broadband transient absorption spectroscopy. Two distinct time regimes are identified, both of which are dominated by unbound charge carriers despite the high exciton binding energy. In the first time regime, the unbound charge carriers cause an increase and a broadening of the exciton absorption band. In the second time regime, a peculiar narrowing of the excitonic absorption profile is observed, which we assign to the presence of built-in fields and/or charged defects. Our results pave the way to analyze spectrally complex transient absorption measurements on layered TMD materials and indicate the potential for ReS2 to produce mobile free charge carriers, a feat relevant for photovoltaic applications.

Electronic structures and optical properties of BiOBr/BiOI heterojunction with an oxygen vacancy

BiOBr/BiOI heterojunction and oxygen vacancy promote the photocatalytic efficiency of BiOX-based catalysts. • Experimentally observed photocatalytic promotion in BiOX catalysts is intepreted. • A built-in field is formed at the interface of BiOBr/BiOI heterostructure. • Oxygen vacancy promotes carrier separation and photocatalytic efficiency. • The combination of heterojunction and O vacancy improves light absorption efficiency. BiOX (X = Br, I) is one of the promising photocatalysts in solar energy conversion, but its photocatalytic efficiency needs further promotion. The BiOBr/BiOI heterostructures with and without an oxygen vacancy are designed and studied by means of first-principles calculations. Compared to monolayer BiOX, the heterostructure has a narrow band gap that favors optical absorption of low-energy light, and forms a built-in field at the interface that facilitates electron-hole separation. The addition of oxygen vacancy produces impurity levels that broaden the optical absorption into the infrared region and promote further the charge carrier separation. Our calculations reveal the origin of enhanced photocatalytic efficiency in the BiOX heterostructures, which is helpful for the design of novel structures with promoted photocatalytic performances.

Enhancing Performance of Broadband Photodetectors Based on Perovskite CsPbBr3 Nanocrystals/ZnO-Microwires Heterostructures

A broadband photodetector response in the ultraviolet (UV)-to-green range (up to 530 nm) based on perovskite CsPbBr3 nanocrystals (NCs)/ZnO-microwires (MWs) heterostructures was realized via a convenient spin-coating method. Under UV light (365 nm) illumination, compared with a bare-ZnO-MW-based photodetector, the CsPbBr3-NCs/ZnO-MWs-heterostructure-based photodetector exhibited a faster photoresponse (<0.1 s) and higher current responsivity (93.50 AW−1), external quantum efficiency (3399%), and detectivity (4.4 × 1010). In addition, the photodetector based on CsPbBr3-NCs/ZnO-MWs heterostructures also exhibited a very fast photoresponse to green light (530 nm). These can be ascribed to the strong light-trapping ability of CsPbBr3 NCs and high charge-transfer efficiency at the CsPbBr3-NCs/ZnO-MWs-heterojunction interface due to the built-in field, which facilitates the spatial separation of the photogenerated carriers. Therefore, this work will develop perovskite/ZnO nanomaterials as promising building blocks for broadband photodetectors and wider optoelectronic applications.

Investigation of internal fields in organic semiconductors in the presence of traps

In an organic semiconductor optoelectronic device, the built-in field within the active layer is typically determined by the difference in contact potentials of the device. However, the presence of space charges and trap states contribute to the electric field within the thin film. Depending on the maximum applied forward voltage, the trap states can be charged, inducing hysteresis in the optoelectronic response of the system. In this work, we investigate the electric fields inside organic photovoltaic device structures, in the presence of traps, using electroabsorption (EA) spectroscopy. Comparing simulations with our experimental results, we explained the origin of hysteresis in the electroabsorption signal as a function of applied DC bias. We solved Poisson’s equation to estimate the densities of trapped carriers in the active layers. The filled trap densities in poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)] (PPDT2FBT) were found to be ∼1×1017 and ∼6×1016 cm−3, respectively. From the transient EA measurements, the estimated values of energies of the trap states with respect to the HOMO level were 0.82 and 0.76 eV in P3HT and 0.70 and 0.64 eV in PPDT2FBT, which indicated the presence of midgap traps in these organic semiconductor thin films. Such trap induced changes in the internal fields within the active layers, affect the mobility and carrier transport in the organic optoelectronic devices. The midgap traps lead to exciton quenching and also act as non-radiative recombination centers, resulting in reduction in luminescence efficiency of the active layers.

Ultrahigh-responsivity deep-UV photodetector based on heterogeneously integrated AZO/a-Ga2O3 vertical structure

ZnO:Al (AZO) and a-Ga2O3 thin films were successively deposited on a sapphire substrate by magnetron sputtering and the photoelectric properties of AZO/a-Ga2O3 heterojunction vertical structure to solar blind ultraviolet light were investigated. The device shows a high photo-to-dark current ratio (2.2 × 103), low dark current (11.4 nA), large responsivity (67.26 A/W) and fast response and recovery times of 1.53 μs and 2.25 ms under 254 nm light illumination at 10 V. Additionally, the device exhibits an obvious self-powered effect with light-dark current ratio (183.3) and the responsivity (2.92 × 10−2 A/W) at 0 V. The high response is attributed to the separation of photogenerated electron-hole pairs due to built-in field in the depletion width of AZO and Ga2O3. The analysis shows that there exists a quasi-Zener tunneling internal gain mechanism, which increases the performance of the device. The comprehensive performance of the device implied a wide potential in optoelectronics applications.

Low temperature deposition of BiFeO3 films on Ti foils for piezoelectric applications

Predominantly (100)-oriented BiFeO3 films with excellent ferroelectric and piezoelectric properties were successfully fabricated on Ti foils via RF-magnetron sputtering at 450 °C. Well-saturated P-E loops with a high remnant polarization (Pr ~72 μC/cm2) and a large built-in field (~145 kV/cm) were observed in the BiFeO3 films. A large transverse piezoelectric coefficient (|e31,f| ~ 2.2 ± 0.2 C/m2) and a decent dielectric property (εr~260–270, tanδ~1.6–2.0%), together with a remarkable fatigue-resistance (~1.1% loss of |e31,f| after 1.2 × 106 piezoelectric actuation cycles) were demonstrated in patterned BiFeO3-Ti cantilevers. These results indicate a great potential of BiFeO3 films as piezo-active components in metal-based micro-electro-mechanical systems (MEMS).

Optically Induced Coherent Phonons in Bismuth Oxyiodide (BiOI) Nanoplatelets

Bismuth oxyiodide (BiOI) is a promising material for photocatalysis combining intriguing optical and structural properties. We show that excitation by a femtosecond laser pulse creates coherent phonons inducing a time-variant oscillating modulation of the optical density. We find that the two underlying frequencies originate from lattice vibrations along the [001] crystallographic axis, the stacking direction of oppositely charged layers in BiOI. This is consistent with a subpicosecond charge separation driven by a built-in dipolar field. This partially screens the field, launching coherent phonons. Further, we determine the two major dephasing mechanisms that lead to the loss of vibronic coherence: (i) the anharmonic decay of an optical phonon into two acoustic phonons and (ii) phonon-carrier scattering. Our results provide a direct demonstration of the presence of an electric field in BiOI along the [001] axis and show its role in efficient charge separation that is crucial for photocatalytic applications of BiOI.

Direct Current Electricity Generation from Dynamic Polarized Water–Semiconductor Interface

Liquid electricity generator and hydrovoltaic technology have received numerous attentions, which can be divided into horizontal movement generator and vertical movement generator. The horizontal movement generator is limited for powering the integrated and miniaturized energy chip as the current output direction is depending on the moving direction of the water droplet, which means a sustainable and continuous direct-current (DC) electricity output can be hardly achieved because of the film of limited length. On the other hand, the existing vertical movement generators include triboelectricity or humidity gradient-based liquid electricity generator, where the liquid or water resource must be sustainably supplied to ensure continuous current output. Herein, we have designed an integratable vertical generator by sandwiching water droplets with semiconductor and metal, such as graphene or aluminum. This generator, named as polarized liquid molecular generator (PLMG), directly converts the lateral kinetic energy of water droplet into vertical DC electricity with an output voltage of up to ~1.0 V from the dynamic water-semiconductor interface. The fundamental discovery of PLMG is related to the non-symmetric structure of liquid molecules, such as water and alcohols, which can be polarized under the guidance of built-in field caused by the Fermi level difference between metal and semiconductor, while the symmetric liquid molecules cannot produce any electricity on the opposite. Integratable PLMG with a large output power of ~90 nW and voltage of ~2.7 V has been demonstrated, meanwhile its small internal resistance of ~250 kilohm takes a huge advantage in resistance matching with the impedance of electron components. The PLMG shows potential application value in the Internet of Things (IoTs) after proper miniaturization and integration.

Enhanced photocatalytic performance of ferroelectric-based SrBi4Ti4O15/SnS2 hybrids by piezoelectric effect

Combining the ferroelectric with semiconductor photocatalyst has been demonstrated as an effective strategy to facilitate the separation of photogenerated electrons and holes, leading to superior synergistic catalytic performance. Herein, SrBi4Ti4O15 (SBTO)/SnS2 hybrids were synthesized, where SnS2 nanostructures were decorated on the surfaces of SBTO nanosheets through a hydrothermal method. The nanostructure of SnS2 could be controlled from nanoparticles to hollow nanoflowers and eventually nanoflowers with increasing concentration of SnCl4. The light absorption capability, photocatalytic activity, and stability of SBTO/SnS2 hybrids were tremendously enhanced, ascribing to the introduction of SnS2 and built-in electric field of ferroelectric SBTO. The introduced periodic magnetic stirring on ferroelectric could resolve the electrostatic screening and help maintain the constant effectiveness of built-in field, promoting the separation of electrons and holes and further improving photocatalytic activity.

Enhanced photocatalytic activity of ferroelectric-based Ag2O/Bi4Ti3O12 hybrids by piezoelectric effect

Combining the ferroelectric/piezoelectric catalysts with photocatalysts was demonstrated as an effective way to facilitate the separation of photoinduced electrons and holes to superior synergistically catalytic activities. In this work, Bi4Ti3O12 (BiTO) nanoflowers were synthesized with Ag2O nanoparticles uniformly decorated on the surfaces, forming xAg2O/BiTO (x = 0–30%) hybrids. The light absorption, photocatalytic activity, and cyclic stability of BiTO nanoflowers were tremendously enhanced after Ag2O decoration. Density functional theory (DFT) calculations have confirmed the large ferroelectric spontaneous polarization along [100] axis in BiTO, which acts as built-in electric field to boost electrons and holes transfer into opposite direction. However, the static built-in electric field can easily be screened by free carriers. To resolve this item, ultrasonic excitation was introduced. The periodic mechanical vibration added on ferroelectrics could maintain the built-in field effective continuously, further improving the photocatalytic activity. Moreover, the ultrasonic frequency and electric poling were found to have influence on the photocatalytic activity. The poled 20%Ag2O/BiTO shows the optimum photocatalytic performance, and the underlying mechanisms were discussed in detail.

Oxygen Vacancy-Enhanced Photoelectrochemical Water Splitting of WO3/NiFe-Layered Double Hydroxide Photoanodes.

Photoelectrochemical (PEC) water splitting serves as one of the promising approaches for producing clean and renewable energy, and their solar-hydrogen energy conversion efficiency depends on the interfacial charge separation and carrier mobility. Herein, we report an effective strategy to promote the PEC performance by fabricating a WO3 photoanode rich in oxygen vacancies (Ov) modified by NiFe-based layered double hydroxide (LDH). When WO3-Ov/NiFe-LDH is used as a photoanode, the maximum photocurrent density at 1.8 V versus RHE has been significantly enhanced to 2.58 mA·cm-2, which is 4.3 times higher than that of WO3. In addition, analogues were studied in controlled experiments without Ov, which further demonstrated that the synergistic effect of NiFe-LDH and Ov resulted in increased carrier concentration and driving force. According to electrical impedance spectroscopy, X-ray photoelectron spectroscopy, and Mott-Schottky analysis, the built-in electronic field in WO3 homojunction, along with the accelerated hole capture by the NiFe-LDH cocatalyst contributes to the improved charge separation and transport in the WO3-Ov/NiFe-LDH electrode. This work proposes an efficient and valuable strategy for designing the structure of WO3-based photoelectrodes.

The design of high performance photoanode of CQDs/TiO2/WO3 based on DFT alignment of lattice parameter and energy band, and charge distribution

Photoanode is the key issue for photoelectrocatalytic (PEC) water splitting and organics degradation. However, it always faces several restrictions including severe photocorrosion, low charge separation and transfer efficiencies, poor visible light harvesting, and sluggish interfacial reaction kinetics, which often required a variety of modifications with only low improvements achieved. Herein, a high performance CQDs/TiO2/WO3 photoanode was designed on the basis of density function theory (DFT) alignment of lattice parameters and energy band, and charge distribution. The TiO2/WO3 heterojunction can abate photocorrosion through the hetero-epitaxial growth of TiO2 (001) on WO3 (002) for the lattice mismatch <3% eliminating dangling bonds, with high corrosion resistance and photostability of TiO2. As the built-in field constructed by a staggered band alignment structure with the valence band offset (VBO) of 0.51 eV, the photogenerated carriers transfer and separation are promoted dramatically. Through the DFT calculations, the sunlight absorption wavelength can be extended, and the interfacial reaction kinetics can be expedited with the modification of carbon quantum dots (CQDs) on TiO2/WO3, due to the narrower bandgap (Eg) and the accumulation of electrons at TiO2 side. The DFT designed CQDs/TiO2/WO3 photoanode significantly increase photocurrent density from 0.90 to 2.03 mA cm−2 at 1.23 V, charge separation efficiency from 56.3 to 79.2% and charge injection efficiency from 51.2 to 70.4%, and extend light absorption edge from 455 to 463 nm over pristine WO3, with better photostability and lower holes-to-water resistance.

Low Temperature Deposition of Bifeo3 Films on Ti Foils for Piezoelectric Applications

Predominantly (100)-oriented BiFeO 3 films with excellent ferroelectric and piezoelectric properties were successfully fabricated on Ti foils via RF-magnetron sputtering at 450 °C. Well-saturated P-E loops with a high remnant polarization ( P r ~72 μC/cm 2 ) and a large built-in field (~145 kV/cm) were observed in the BiFeO 3 films. A large transverse piezoelectric coefficient (| e 31,f | ~ 2.2± 0.2 C/m 2 ) was demonstrated in patterned BiFeO 3 -Ti cantilevers, together with a high piezoelectric figure of merit (~2.1 GPa), a large voltage response (~0.96 GV/cm) and a remarkable fatigue-resistance (~1.1% loss of | e 31,f | after 1.2×10 6 actuation cycles). These results indicate a great potential of BiFeO 3 films as piezo-active components in metal-based micro-electro-mechanical systems (MEMS).

Optical Distance Measurement Based on Induced Nonlinear Photoresponse of High-Performance Organic Near-Infrared Photodetectors

Extraction barriers are usually undesired in organic semiconductor devices since they lead to reduced device performance. In this work, we intentionally introduce an extraction barrier for holes, leading to nonlinear photoresponse. The effect is utilized in near-infrared (NIR) organic photodetectors (OPDs) to perform distance measurements, as delineated in the focus-induced photoresponse technique (FIP). The extraction barrier is introduced by inserting an anodic interlayer with deeper highest occupied molecular orbital (HOMO), compared to the donor material, into a well-performing OPD. With increasing irradiance, achieved by decreasing the illumination spot area on the OPD, a higher number of holes pile up at the anode, counteracting the built-in field and increasing charge-carrier recombination in the bulk. This intended nonlinear response of the photocurrent to the irradiance allows determining the distance between the OPD and the light source. We demonstrate fully vacuum-deposited organic NIR optical distance photodetectors with a detection area up to 256 mm2 and detection wavelengths at 850 and 1060 nm. Such NIR OPDs have a high potential for precise, robust, low-cost, and simple optical distance measurement setups.