External Quantum Efficiency Values Research Articles

Cliff-like conduction band offset at CdS/Cu2ZnSnS4 heterojunction prepared by sputtering CuSn alloy target using different stacking order

The uniformly distributed Cu2ZnSnS4 (CZTS) thin films were grown by a simply sputtered method using two sputtered stacking order: ZnS/CuSn/Mo/SLG (T1) and CuSn/ZnS/Mo/SLG (T2). The highly crystalline tetragonal structure CZTS with Cu-poor, Zn-rich composition was obtained in the two samples. Grain size of the sample T1 was larger than that of sample T2 and some voids appeared in T2 caused by the SnS evaporation during sulfurization. Raman and XPS measurements showed that sample T2 had a small amount secondary phase of ZnS at CZTS/Mo interface, while T1 did not. The CZTS solar cell devices (named D1 and D2) based on the two stacking order were fabricated using CdS buffer layer. The conversion efficiency of 5.22% was obtained from D1, higher than that of 2.53% from D2. The maximum value of external quantum efficiency was 74.6% (D1) and 55.1% (D2) respectively. Accordingly, the device D1 exhibited a higher Voc of 531 mV and Rsh of 698.85 Ωcm2 than that of 481 mV and 286.73 Ωcm2 from the D2, which resulted in the higher fill factor in D1. The effect of the stacking order on conduction band offset (CBO) at CdS/CZTS heterojunction was studied. The typical cliff-like CBO was calculated as 0.22 eV for sample D1 and 0.34 eV for D2. The Cd1-xZnxS were found at the heterojunction in D1 using Zn source layer as the outermost, which made the band alignment smoother. The ZnS/CuSn/Mo/SLG stacking order with smaller CBO can reduce the loss of Voc and greatly improve the performance of solar cells.

An efficient wide range photodetector fabricated using a bilayer Bi2S3/SnS heterojunction thin film

This study presents a detailed optoelectronic investigation on the bilayer Bi2S3/SnS heterojunction photodetector. The Bi2S3 and SnS nanostructures were synthesized by an ultrasonication method and deposited in the form of thin films by a thermal evaporation system to fabricate the photodetectors. The performed optoelectrical measurements showed that the Bi2S3 and Bi2S3/SnS photodetectors are respectively n- and p-type electrical conductivity. This finding was further confirmed by current–voltage (I–V) analysis, Mott–Schottky plots and photoresponse measurements. According to the obtained gain and sensitivity values, the Bi2S3/SnS heterojunction provides a higher photon-to-electrical carrier conversion relative to the Bi2S3 photodetectord due to the enhanced photogeneration of electron–hole pairs and separation of the photoinduced charge carriers under the influence of the electric field build-in at the heterojunction’s interface. The heterojunction exhibited a remarkable photoresponse from 400 to 800 nm by giving the photocurrent gain (G), sensitivity (S), and external quantum efficiency (EQE) values of 8460%, 450% and 45%, respectively. The obtained results represent the Bi2S3/SnS heterojunction photodetector as a potential candidate for devising high-performance optoelectronic devices.

High-Detectivity Perovskite Light Detectors Printed in Air from Benign Solvents

Summary Here, we propose a simple and low-temperature approach for the synthesis of methylammonium lead halide perovskite inks based on sub-micrometer-sized particles with tunable band gap. The particles allow the formulation of inks in benign solvents, such as propan-2-ol, and the printing of the photoactive layers of planar photoconductors with scalable, large-area coating techniques under ambient conditions. When surface traps are passivated with [6,6]-phenyl-C61-butyric acid methyl ester fullerene (PCBM), a high photoconductive gain (exceeding 200 in the blue) and reduced noise produce record-high specific detectivities exceeding 7 × 1013 cmHz0.5/W and gain-bandwidth product values of 7.5 × 106 Hz. Given the extreme simplicity of the presented device architecture and the straightforward processing, yielding printable light detectors rivalling established technologies, the present work promises a short-term deployment of printed perovskite detectors in a multitude of opto-electronic applications.

Efficient blue fluorescent emitters based on imidazole-pyridine derivatives for organic light-emitting diodes

Imidazole-pyridine derivatives such as 2-(1-phenyl-5-(pyridin-2-yl)-1H-imidazol-4-yl)pyridine were synthesized for the efficient blue light-emitting materials. OLED devices using these materials were fabricated in the following sequence; Indium tin oxide (ITO) (150 nm)/N,N'-diphenyl-N,N'-(2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) (50 nm)/Tris(4-carbazoyl-9-ylphenyl)amine (TCTA) (10 nm)/Blue materials (20 nm)/2,2′,2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) (30 nm)/Lithium quinolate (Liq)/Aluminum (Al) (2/100 nm). Particularly, a device using 9,10-dihydro-9,9-dimethyl-10-(4-(1-phenyl-4,5-di(pyridin-2-yl)-1H-imidazol-2-yl)phenyl)acridine as a blue emitter showed maximum values of luminous efficiency, power efficiency, and external quantum efficiency of 0.21 cd/A, 0.10 lm/W, 0.26% at 20 mA/cm2, respectively with the Commission Internationale d’Énclairage (CIE) (x,y) coordinates of (0.19, 0.11) at 6.0 V.

High-performance visible light photodetector based on TlGaSSe single crystal

Herein, we present the results of high-performance visible light photodetector fabricated from the grown TlGaSSe single crystal for the first time. The growth direction was found to be (1 0 0) and layered structure was confirmed by scanning electron microscope (SEM) micrograph. The photocurrent observed to be increased with increasing the light intensity and voltage. The photo responsitivity (R), detectivity (D) and external quantum efficiency (EQE) were studied for the fabricated device. The maximum value of R is found to be ∼980 mA V−1. The D value shows a decrease with increasing the light intensity and found in a range of 4.41 × 1011 to 8.48 × 1010 Jones. Further, the maximum value of EQE was found ∼193% at a light intensity of 10 μW cm−2. Photoswitching behavior of the device was also studied and displayed that the ratio of on and off photo values ∼45:100. The values of growth and decay time were found to be ∼218 and 185 ms, respectively.

Thin Film Formation and Photovoltaic Application of Transition Metal Dichalcogenides By Liquid Exfoliation

We studied on a liquid exfoliation technique for the robust production of transition metal dichalcogenides (TMDC) thin films, because this technique has advantages for residue-free, large-scale, and low-cost fabrication. During the process of liquid exfoliation, a mixture of DI water and ethanol was used to obtain higher concentrations of TMDC flakes in the solution compared to that in water-based solution. The film thicknesses were controlled by a two-step centrifuge process to analyze the influence on the photovoltaic properties with gold/TMDC/silicon geometry. Based on ultraviolet photoelectron spectroscopy measurement results, the energy band diagram of the devices using MoS2 and WS2 films were constructed. The external quantum efficiency (EQE) and power conversion efficiency (PCE) were measured as a function of film thickness. The maximum EQE values of MoS2 and WS2 devices are 63.7 and 58.5%, respectively, which are higher than the maximum EQE values of 23% from the Au/Si/In device. PCE of 126-nm-thick MoS2 and 132-nm-thick WS2 film devices appeared 3.55 and 2.98%, respectively, under 100 mW cm-2 solar illumination. These photovoltaic properties could be further improved by enhancing the film coverage and reducing the amount of surface oxidation and impurities. This work shows the potential of using MoS2 and WS2 films in highly efficient photovoltaic devices and other applications due to the various advantages of the liquid exfoliation method.

New Mixed‐C^N Ligand Tris‐Cyclometalated IrIII Complexes for Highly‐Efficient Green Organic Light‐Emitting Diodes with Low Efficiency Roll‐Off

This article reports new tris‐cyclometalated IrIII complexes containing mixed‐C^N ligands, (C^N1)2Ir(C^N2), which are a rarely explored class of complexes. Two mixed 2‐phenylpyridine (ppy)/4‐methyl‐2,5‐diphenylpyridine (mdp) complexes (ppy)2Ir(mdp) 3 and (ppy)Ir(mdp)2 4 have been synthesized and their optoelectronic properties have been systematically characterized. Photoluminescence quantum yield values are 0.76–0.85; excited state lifetimes are 0.07–0.11 µs. Phosphorescent organic light emitting devices (PhOLEDs) based on these emissive complexes in a very simple device architecture reproducibly showed slightly higher external quantum efficiency (EQE) and power efficiency (PE) values compared with devices using the analogous conventional homoleptic Ir complexes Ir(ppy)3 and Ir(mdp)3, and the heteroleptic complexes (ppy)2Ir(acac) and (mdp)2Ir(acac). The new complexes (ppy)2Ir(mdp) 3 and (ppy)Ir(mdp)2 4 give PhOLEDs with EQEmax and PEmax values of 26.7 and 26.0 %/94.7 and 94.1 lm W–1, respectively, and very high values are retained at the practical luminances of 100 and 1000 cd m–2. The values for (ppy)2Ir(mdp) are 26.3 % and 73.6 lm W–1 (at 100 cd m–2) and 24.6 % and 53.5 lm W–1 (at 1000 cd m–2). These efficiencies are comparable with the highest reported values of PhOLEDs using conventional IrIII emitters in more complicated device structures. Mixed C^N ligand systems are, therefore, a viable strategy for developing new efficient phosphorescent emitters.

Reduced graphene oxide-based broad band photodetector and temperature sensor: effect of gas adsorption on optoelectrical properties

Reduced graphene oxide (rGO) has found tremendous application due to its versatile and tunable properties. We have prepared rGO by the green hydrothermal method without using any toxic additives that comprise ~ 5–14 layers with an average interlayer distance of 3.5 A. A device with Ag-rGO-Ag configuration has been fabricated that exhibits excellent stable and reproducible photoresponse properties ranging from UV-VIS (ultraviolet-visible) to the near IR (infrared) region. Responsivity and external quantum efficiency (EQE) values are as high as 0.71, 0.733, 0.230, and 0.313 A W−1 and 57, 85, 88, and 120% using 1550, 1064, 632, and 325 nm wavelength, respectively. We have shown that the temperature-dependent resistance follows a well-definite exponential behavior which indicates potential application of rGO as temperature sensor. Overall, these results suggest that rGO can be a potential material for low-cost, environment-friendly, and efficient broadband photodetector and temperature sensor. Also, pressure-dependent optoelectrical measurements have been carried out that reveal adsorption characteristics of various gases.

High-performance crystalline organic light-emitting diodes based on multi-layer high-quality crystals

Abstract Crystalline organic light-emitting diodes (OLEDs) are of great potential for the applications in solid-state lighting and electrically pumped organic lasers. Now the performance of crystalline OLEDs is poor because those devices typically use a single organic material with unmatched electron and hole mobilities resulting in imbalance charge injection. Here, we fabricate a crystalline OLED with a multi-layer architecture based on high-quality crystalline films. The device exhibits low driving voltage and high efficiency due to balanced charge injection and exciton confinement. An external quantum efficiency (EQE) of 2.41% is achieved, and the EQE value is the highest efficiency in the field of crystalline OLEDs to date. We expect that our results will be a starting point for further research, providing high-performance crystalline OLEDs for solid-state lighting and electrically pumped organic lasers.

Inverted Device Architecture for Enhanced Performance of Flexible Silicon Quantum Dot Light-Emitting Diode.

Here we report for the first time highly flexible quantum dot light-emitting diodes (QLEDs), in which a layer of red-emitting colloidal silicon quantum dots (SiQDs) works as the optically active component, by replacing a rigid glass substrate with a thin sheet of polyethylene terephthalate (PET). The enhanced optical performance for electroluminescence (EL) at room temperature in air is achieved by taking advantage of the inverted device structure. Our QLEDs do not exhibit parasitic EL emissions from the neighboring compositional layers or surface states of QDs over a wide range of driving voltages and do not exhibit a shift in the EL peak position as the operational voltage increases. Compared to the previous Si-QLEDs with a conventional device structure, our QLED has a longer device operational lifetime and a long-lived EQE value. The currently obtained brightness (∼5000 cd/m2), the 3.1% external quantum efficiency (EQE), and a turn-on voltage as low as 3.5 V are sufficiently high to encourage further developments of Si-QLEDs.

Comparison of Electrical and Photoelectrical Properties of ReS2 Field-Effect Transistors on Different Dielectric Substrates.

As one of the newly discovered transition-metal dichalcogenides (TMDs), rhenium disulfide (ReS2) has been investigated mostly because of its unique characteristics such as the direct band gap nature even in bulk form, which is not prominent in other TMDs (e.g., MoS2, WSe2, etc.). However, this material possesses a low mobility and an on/off ratio, which restrict its usage in high-speed and fast switching applications. Low mobilities or on/off ratios can also be caused by substrate scattering as well as environmental effects. In this study, we used few-layer ReS2 (FL-ReS2) as a channel material to investigate the substrate-dependent mobility, current on/off ratio, Schottky barrier height (SBH), and trap density of states of different dielectric substrates. The hexagonal boron nitride (h-BN)/FL-ReS2/h-BN structure was observed to exhibit a high mobility of 45 cm2 V-1 s-1, current on/off ratio of about 107, the lowest SBH of about 12 mV at a zero back-gate voltage ( Vbg), and a low trap density of states of about 5 × 1013 cm-3. These quantities are reasonably superior compared to the FL-ReS2 devices on SiO2 substrates. We also observed a nearly 5-fold improvement in the photoresponsivity and external quantum efficiency values for the FL-ReS2 devices on h-BN substrates. We believe that the photonic characteristics of TMDs can be improved by using h-BN as the substrate and capping layer.

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Summary Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces.

High performance blue-emitting organic light-emitting diodes from thermally activated delayed fluorescence: A guest/host ratio study

Emitters displaying thermally activated delayed fluorescence (TADF) can lead to highly efficient organic light-emitting diodes (OLEDs). Such emitters are usually incorporated into the emissive layer (EML) at a relatively low concentration (<20 wt. %) with respect to a host material, a guest-host approach inherited from conventional fluorescent or phosphorescent OLEDs. Here, detailed studies on OLEDs, in which the concentration of oBFCzTrz (a blue-emitter displaying TADF) in a DPEPO host was varied from 8 to 100 wt. %, reveals that oBFCzTrz displays ambipolar transport and limited fluorescence-quenching due to aggregation. For instance, a neat film of oBFCzTrz maintains a photoluminescence quantum yield of 82%. We demonstrate that OLEDs with an EML having an oBFCzTrz concentration of 50 wt. % in DPEPO yield a maximum external quantum efficiency (EQE) of 25.5% with an EQE roll-off of 10% in the range from 10 to 1000 cd/m2 and Commission Internationale de l'Eclairage color coordinates of (0.20, 0.44). OLEDs with smaller or larger oBFCzTrz concentrations display smaller maximum EQE values. OLEDs with a neat oBFCzTrz EML display a maximum EQE of 14.0%. Time-resolved electroluminescent decay studies, and analysis using a simple model, reveal significant differences in transport, trapping, and recombination in these devices.

Investigation of S-shaped current-voltage characteristics in high-performance solution-processed small molecule bulk heterojunction solar cells

The appearance of an S-shaped current-voltage curve and its impact on the performance of solution-processed small molecule p-DTS(FBTTh2)2:PC70BM bulk heterojunction solar cell devices were investigated. The power conversion efficiency of the devices showing S-curve characteristics was almost half of what was expected for this combination of materials, which was due to a low fill factor (FF) and 20% lower short circuit current density. A normal diode-like current-voltage curve was retrieved when the PCBM content of the active layer was increased, with power conversion efficiency reaching 6%. Analysis of the current-voltage characteristics of the S-curve solar cell devices showed that the effective voltage of the devices throughout the active layer was diminished due to an energy barrier. As a result, the charge collection efficiency was significantly affected. In addition, smaller external quantum efficiency (EQE) values in the absorption range of the small molecule donor in the S-curve devices suggested that charge generation was also affected. Recombination dynamics of both the normal and S-curve devices under steady-state conditions were quite similar. However, photovoltage decay results showed a distinguished pattern of recombination at open circuit conditions in the S-curve devices. This suggested different recombination rates at the cathode and anode electrodes, which is possibly due to the different composition of the donor-acceptor film near the contacts.

Triangulene-based Efficient Exciton Blocking Material for Organic Light-emitting Diodes

Phosphorus-centered 4,8,12-triazatriangulene was identified as an efficient exciton blocking material for phosphorescent organic light-emitting diodes (PHOLEDs). The external quantum efficiency values of Ir(ppy)3-based green PHOLEDs were greatly improved to 20% at 1000 cd m−2.

Eco-Friendly NaSbS2 Quantum Dot-Sensitized Solar Cells

Ternary sulfide NaSbS2 is a low-cost, environmentfriendly semiconductor that has rarely been studied. This paper demonstrates, for the first time, solid-state NaSbS2 quantum dot-sensitized solar cells (QDSSCs). NaSbS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles were synthesized using the sequential ionic layer adsorption reaction method. Solid-state QDSSCs were fabricated from the synthesized nanoparticles using spiro-OMeTAD as the hole-transporting electrolyte. The best cell yielded an efficiency of 1.27% under 1 sun. At the reduced light intensity I0 of 10% sun, the efficiency increased significantly to 4.11% with an open-circuit voltage Voc of 0.51 V, a short-circuit current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> of 1.68 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and a fill factor (FF) of 47.8%. A sublinear power law of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> ∝ I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sup> accounts for the large improvement in performance under low-light intensities because of the reduced carrier recombination. The external quantum efficiency (EQE) spectrum covered the spectral region of 300-750 nm with a maximum EQE value of 72% at λ = 450 nm. The present efficiency (4.11%) represents about 30% improvement over the best previous result (3.18%) of liquid-junction QDSSCs. The respectable efficiency indicates that NaSbS2 shows potential as an efficient solar absorber material.

Organic Photodetectors with Gain and Broadband/Narrowband Response under Top/Bottom Illumination Conditions

AbstractOrganic photodetectors (OPDs) possessing broadband/narrowband photodetection capability and gain have great potential in integrated optoelectronics products. In this work, OPDs with a device structure of ITO/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/thick active layer/semitransparent Al electrode exhibit the extraordinary functions, gain and bidirectional photodetection capability with tunable spectral response range. For the binary OPDs with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) (100:1, wt/wt) as active layer, the OPDs exhibit narrowband response from 620 to 700 nm with full‐width at half maximum (FWHM) of ≈30 nm under bottom illumination condition and broadband response from 300 to 700 nm under top illumination condition, respectively. To further confirm and optimize the extraordinary functions of OPDs, ternary devices are fabricated with P3HT:poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dit‐hiophene‐co‐3‐fluor‐othieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th):PC71BM (50:50:1, wt/wt) as active layer. The narrowband response can be adjusted to near infrared (NIR) region from 760 to 860 nm. The broadband response can be extended to NIR region with response range from 300 to 860 nm. Meanwhile, external quantum efficiency (EQE) spectral shape of the ternary OPDs becomes flatter under top illumination condition and can be kept constant under different bias. The ternary OPDs exhibit similar EQE values of ≈2000% and specific detectivity larger than 1011 Jones at −50 V bias under bottom and top illumination conditions.

Conjugated Polyelectrolytes as Efficient Hole Transport Layers in Perovskite Light-Emitting Diodes.

Perovskite-based optoelectronic devices have been rapidly developing in the past 5 years. Since the first report, the external quantum efficiency (EQE) of perovskite light-emitting diodes (PeLEDs) has increased rapidly through the control of morphology and structure from 0.1% to more than 11%. Here, we report the use of various conjugated polyelectrolytes (CPEs) as the hole injection layer in PeLEDs. In particular, we find that poly[2,6-(4,4-bis-potassium butanylsulfonate)-4 H-cyclopenta-[2,1- b;3,4- b']-dithiophene)] (PCPDT-K) transfers holes effectively, blocks electron transport from the perovskite to the underlying ITO layer, and reduces luminescence quenching at the perovskite/PCPDT-K interface. Our optimized PeLEDs with PCPDT-K show enhanced EQE by a factor of approximately 4 compared to control PeLEDs with PEDOT:PSS, reaching EQE values of 5.66%, and exhibit improved device stability.

New multifunctional aggregation-induced emission fluorophores for reversible piezofluorochromic and nondoped sky-blue organic light-emitting diodes

In this study, 4,6-diphenyl-1,3,5-triazine as the rotor, was firstly introduced to the construction of AIEgens. By conjugating phenyl-9H-carbazole and 4,6-diphenyl-1,3,5-triazine to the 9 or 10 position of anthracene, three new multifunctional aggregation-induced emission (AIE) fluorophores, 3-(10-(4,6-diphenyl-1,3,5-triazin-2-yl)anthracen-9-yl)-9-phenyl-9H-carbazole (3CzAnTrz) 9-(4-(10-(4,6-diphenyl-1,3,5-triazin-2-yl)anthracen-9-yl)phenyl)-9H-carbazole (pCzAnTrz) and 9-(3-(10-(4,6-diphenyl-1,3,5-triazin-2-yl)anthracen-9-yl)phenyl)-9H-carbazole (mCzAnTrz) were designed and synthesized. The photophysical properties indicated that all three compounds not only exhibited an AIE effect but also showed a reversible piezofluorochromic (PFC) behaviour. The experimental results revealed that the spectral shifts ΔλPFC (ΔλPFC = λrepressed – λannealed) were obviously influenced by the linking position of 9-phenyl-9H-carbazole, and 3CzAnTrz showed largest spectral shifts (ΔλPFC = 66 nm), because of the relatively loose molecular packing, weak intermolecular CH-π interactions and more twisted conformation. When three fluorophores were used as emitter in the nondoped sky-blue devices, these devices showed excellent electroluminescence (EL) performances, realizing the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) values of 13.34 cd A−1, 11.59 lm W−1, 5.44%; 11.19 cd A−1, 9.25 lm W−1, 5.54% and 8.74 cd A−1, 6.44 lm W−1, 4.71% for 3CzAnTrz, pCzAnTrz, and mCzAnTrz, respectively. And these devices exhibit negligible efficiency roll-off even at 10000 cd m−2. These results manifest that the potential advantage of multifunctional AIEgens applicable for piezofluorochromism and nondoped high-performance EL devices.

Photovoltaic property of n-ZnO/p-Si heterojunctions grown by pulsed laser deposition

Zinc oxide (ZnO) thin films were grown on p-Si substrates under various oxygen partial pressure (p(O2)) from 5.3 to 9.3 Pa by using pulsed laser deposition. In x-ray diffraction analysis, n-ZnO thin film grown under an p(O2) of 8 Pa showed the highest intensity of (002) diffraction peak and highly c-axis oriented. At room temperature, all the n-ZnO thin films grown at various p(O2) showed near band edge emissions about 385 nm, and the performance of n-ZnO/p-Si heterojunction grown at p(O2) of 8 Pa shows better than that of the heterojunction with n-ZnO layer grown at p(O2) of 5.3, 6.7, and 9.3 Pa. The performance of the heterojunction with and without Al-doped ZnO (AZO) layer was more improved by post-annealing at 200 °C, so that the heterojunction with and without AZO layer showed power conversion efficiency (PCE) of 0.61% and 1.5%, respectively. By measurement of external quantum efficiency (EQE), it was found that the improved PCE of the heterojunction with AZO layer was attributed to the overall enhanced EQE values from ultraviolet to near infrared.