Effective Surface Passivation Research Articles

Surface Passivation Treatment to Improve Performance and Stability of Solution-Processed Metal Oxide Transistors for Hybrid Complementary Circuits on Polymer Substrates.

Hybrid integration of n‐type oxide with p‐type polymer transistors is an attractive approach for realizing high performance complementary circuits on flexible substrates. However, the stability of solution‐processed oxide transistors is limiting the lifetime and reliability of such circuits. Oxygen vacancies are the main defect degrading metal oxide transistor performance when ambient oxygen adsorbs onto metal oxide films. Here, an effective surface passivation treatment based on negative oxygen ion exposure combined with UV light is demonstrated, that is able to significantly reduce surface oxygen vacancy concentration and improve the field effect mobility to values up to 41 cm2 V−1 s−1 with high on–off current ratio of 108. The treatment also reduces the threshold voltage shift after 2 days in air from 5 to 0.07 V. The improved stability of the oxide transistors also improves the lifetime of hybrid complementary circuits and stable operation of complementary, analog amplifiers is confirmed for 60 days in air. The suggested approach is facile and can be widely applicable for flexible electronics using low‐temperature solution‐processed metal oxide semiconductors.

Defect Engineering for High-Performance Microscale Light-Emitting Diode Devices By Surface Passivation

Microscale light-emitting diodes (µLEDs) are regarded as the cornerstone of next-generation display technology to meet the personalized demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors, and ultrahigh definition TVs. However, the ratio of the sidewall area to the emitting area increases as the pixel size of µLEDs becomes small, which can increase the possibility of the non-radiative recombination process near the active layer resulting in a low efficiency of µLEDs. To overcome these issues, in general, a passivation layer such as SiO2, SiNx, and Al2O3 has been applied to passivate dangling bonds near the surface of the sidewall to ruduce surface defects. In addition, heat treatment method has been used for curing the defect sites near the sidewall to maximize the effect of surface passivation; however, there are few reports on the analysis of curing mechanism considering carrier dynamics and/or devcie performance of µLEDs using various materials of passiation layer.In this regard, we studied the performance of µLEDs depending on the passivation layer (SiO2, SiNx, Al2O3) by considering charge distribution and carrier dynamics near the sidewall region. First, X-ray photoelectron spectroscopy was conducted to investigate what kind of bonds are formed between the atoms. Based on this analysis, we verified oxygen and nitrogen atoms are closely associatted with the amount of passivated states, which also confirmed by capacitance-voltage characteristics via keithley measurment system. In addtion, photnoluminescence (PL) efficiencies depending on the passivation layer were measured to understand the carrier dynamics of µLED devices using temperature-dependent PL measurement system (18–300 K). As a result, PL efficiency of the sample with the passivation layer was enhanced by 15% (SiO2), 6% (SiNx), and 12% (Al2O3) compared to that of the sample without passivation layer, which can be attributed to the removed non-radiatve defects near the sidewall area after passivation. More detailed experimental results and device performance of µLEDs will be presented at the conference.

Investigation of the structural and electronic properties and surface passivation influence on electronic properties of (001) SbNSr3 nano-surfaces: A hybrid DFT study

In this research, the (001) nano-surfaces of SbNSr3 with SbSr and NSr2 terminations are investigated using the hybrid density functional theory (DFT) calculations. The structural, energetic, and electronic properties and also surface passivation effects are studied for different thicknesses of the nano-surfaces. The calculations showed that the surface rumpling of the SbSr termination was larger than that of the NSr2 termination. The surface energy evaluation indicated that the difference in surface energy for the two terminations of (001) SbNSr3 nano-surfaces was about 0.002 eV/Å2. Therefore, it can be said that both SbSr- and NSr2-terminated (001) surfaces of SbNSr3 are stable. Both types of nano-surfaces demonstrated a metallic nature due to the surface states while the bulk has a semiconducting character. Hydrogen atoms were used for surface passivation to remove the surface states in the band gap. The hydrogen passivation opened the band gap for both types of nano-surfaces. The calculated band gap of the SbSr termination was smaller than that of the NSr2 termination. The opened band gap in the SbSr-terminated nano-surfaces with the thicknesses of 3L–9L varied between 0.672 eV, 0.415 eV, 0.840 eV, and 0.808 eV. The calculated band gaps of the NSr2-terminated nano-surfaces were 1.776, 1.033, 1.249, and 1.029 eV for the thicknesses of 3L, 5L, 7L and, 9L, respectively.

Effective suppression of nanotextured black silicon surface recombination channels by aluminum oxide: comparison from sputtered and ALD grown films

Effective surface passivation of nano-textured silicon (NT-Si) using sputtered aluminum oxide (AlO x ) films is demonstrated and compared with the atomic layer deposition (ALD) grown AlO x films. Silver-assisted wet chemical etching is used to obtain sub-wavelength size features of black NT-Si, and then the NT-Si surface is chemically polished to minimize the surface defect states that act as trap centres for charge carriers. The NT-Si surface passivation is characterized by the density of interface trap states (D it) and the fixed charge density (Q f), which also correlate with the surface recombination rate (S eff). For the sputtered AlO x films, the estimated D it and Q f are ∼4 × 1011 eV−1 cm−2 and ∼7 × 1012 cm−2, respectively, yielding the S eff of ∼34 cm s−1. Whereas, for the ALD AlO x films the estimated D it, Q f, and S eff are ∼1.6 × 1011 eV−1 cm−2, ∼7.4 × 1012 cm−2, and ∼20 cm s−1, respectively. The chemical and field-effect passivation are evident for the ALD AlO x films with the reduced S eff. However, the sputtered AlO x films have shown only an indication of field-effect passivation with a small variation in the Q f. Still, the observed larger D it is due to the sputtering damage on the NT-Si surface compared to ALD AlO x films.

Slow Passivation and Inverted Hysteresis for Hybrid Tin Perovskite Solar Cells Attaining 13.5% via Sequential Deposition.

Herein, we report a sequential deposition procedure to passivate the surface of a hybrid mixed cationic tin perovskite (E1G20) with phenylhydrazinium thiocyanate (PHSCN) dissolved in trifluoroethanol solvent. The photoluminescence lifetime of the PHSCN film was enhanced by a factor of 6, while the charge-extraction rate from perovskite to C60 layer was enhanced by a factor of 2.5, in comparison to those of the E1G20 film. A slow surface passivation was observed; the performance of the PHSCN device improved upon increasing the storage period to attain an efficiency of 13.5% for a current-voltage scan in the forward bias direction. An inverted effect of hysteresis was observed in that the efficiency of the forward scan was greater than that of the reverse scan. An ion-migration model as a result of the effect of the phenylhydrazinium surface passivation is proposed to account for the observed phenomena. The device was stable upon shelf storage in a glovebox for 3000 h.

Effective surface passivation on CsPbBr3 nanocrystals via post-treatment with aromatic carboxylic acid

Surface defects on CsPbX3 nanocrystals (NCs) commonly lead to the degeneration of photoluminescence emission and stability of CsPbX3 NCs. Defect passivation by surface engineering provides an effective route to improve the optical properties and stability. In this work, a series of aromatic carboxylic acids were explored to modify the as-synthesized CsPbBr3 NCs. The surface defects of CsPbBr3 NCs are found to be effectively passivated via the binding of carboxyl group with uncoordinated Pb2+ on the surface of CsPbBr3 NCs. The coordination ability of carboxyl groups with Pb2+ can be regulated by the electron effect generated by different groups at the para-position of carboxyl groups, thereby adjusting the passivation of surface defects. Benefitting from the effective passivation of surface defects, the PL emission and stability of the CsPbBr3 NCs can be effectively enhanced. Among them, the CsPbBr3 NCs modified with the softest 4-(trifluoromethyl)benzoic acid show near-unity photoluminescence quantum yields, a single-exponential photoluminescence decay kinetics and excellent stability.

High gain GaN ultraviolet Schottky photodetector with Al-doped ZnO interlayer

We fabricated an GaN Schottky photodiode (PD) with Al-doped ZnO (AZO) interlayer for ultraviolet (UV) photodetection, and its optoelectrical properties with a comparison to the GaN Schottky PD without AZO interlayer. The AZO-interlayered GaN Schottky PD was highly sensitive to 350 nm laser irradiation, having a photoresponsivity of 11.1 AW–1 and detectivity of 1.04 × 1012 cm·Hz1/2·W–1 at -2 V as against 0.28 AW−1 and 2.23 × 1010 cm·Hz1/2·W–1 for the GaN Schottky PD without AZO interlayer. The transient photoresponse revealed a rise and decay time of 203 and 293 ms, respectively for the AZO-interlayered GaN Schottky PD. The introduction of AZO interlayer resulted in a reduction in the noise spectral density, leading to an increase in the detectivity by more than an order, as compared to GaN Schottky PD without AZO interlayer. An improved photodetection behavior of the AZO-interlayered GaN Schottky PD could be ascribed to effective GaN surface passivation and reduction of the surface states by the AZO interlayer. The utilization of the AZO in GaN-based UV photodetectors can provide a potential and simplistic approach towards the fabrication of high performance GaN-based UV photodetectors.

Ultrathin Aluminum Oxide Films Induced by Rapid Thermal Annealing for Effective Silicon Surface Passivation

A novel method of preparing ultrathin aluminum oxide films by rapid thermal annealing (RTA) treatment for effective silicon surface passivation is proposed. The high‐temperature RTA processing (750–825 °C) for tens of seconds in an oxygen atmosphere completely converts the thermally evaporated aluminum metal nanofilms (1–5 nm) on crystalline silicon to aluminum oxide (Al2O3) films, with a thin SiOx layer formed at the interface between the silicon and the Al2O3. The generated Al2O3 film can provide superior passivation quality for the silicon surface, even better than that obtained by the thermal atomic layer deposition technique. Moreover, the growth kinetics of the Al2O3 passivating film indicates that it is a diffusion‐controlled activation process, with an energy barrier of 3.3 eV for aluminum ions diffusing across the metal/oxide interface.

A stable nanosilver decorated phosphorene nanozyme with phosphorus-doped porous carbon microsphere for intelligent sensing of 8-hydroxy-2′-deoxyguanosine

Nanozyme based on the silver nanoparticles (AgNPs) decorated highly water-oxygen stable phosphorene (BP) nanohybrid with phosphorus-doped porous carbon microspheres (P-PCMs) is applied as an intelligent sensing platform for the electrochemical detection of 8-hydroxy-2′-deoxyguanosine (8-OHdG) as a biomarker of oxidative DNA damage in human urine sample. The density functional theory (DFT) is use for investigating the effect of silver on the conductivity level of BP and discussing a possible mechanism for the electrocatalytic oxidation of 8-OHdG. The Ag+ is in-situ reduced as AgNPs that grows onto the BP surface for the controllable preparation of BP-AgNPs with effective surface passivation among different metal ions decorated BP. P-PCMs with 4.9-fold enhancement in specific surface area (1636.73 m2 g−1) are prepared by hydrothermal carbonization of α-cyclodextrin as carbon sources, then calcinate in the presence of phosphoric acid as an activator and dopant. P-PCMs-BP-AgNPs are prepared by the ultrasound-assisted liquid-phase exfoliation with the addition of Ag+, and both P-PCMs and black phosphorus crystals are sufficiently grinded. The P-PCMs-BP-AgNPs nanohybrid displays good long-term water-oxygen stability, extraordinary specific surface area, superior electrocatalytic capacity with 303-fold enhancement, enzyme-like characteristics with Imax of 100 μA and Km of 29 μM. The machine learning (ML) model with artificial neural network (ANN) algorithm is employed for the intelligent output of 8-OHdG in real sample with acceptable recovery in work range from 0.2 to 125 μM.

In situ passivation of Ga x In(1−x)P nanowires using radial Al y In(1−y)P shells grown by MOVPE

Ga x In(1−x)P nanowires with suitable bandgap (1.35–2.26 eV) ranging from the visible to near-infrared wavelength have great potential in optoelectronic applications. Due to the large surface-to-volume ratio of nanowires, the surface states become a pronounced factor affecting device performance. In this work, we performed a systematic study of Ga x In(1−x)P nanowires’ surface passivation, utilizing Al y In(1−y)P shells grown in situ by using a metal-organic vapor phase epitaxy system. Time-resolved photoinduced luminescence and time-resolved THz spectroscopy measurements were performed to study the nanowires’ carrier recombination processes. Compared to the bare Ga0.41In0.59P nanowires without shells, the hole and electron lifetime of the nanowires with the Al0.36In0.64P shells are found to be larger by 40 and 1.1 times, respectively, demonstrating effective surface passivation of trap states. When shells with higher Al composition were grown, both lifetimes of free holes and electrons decreased prominently. We attribute the acceleration of PL decay to an increase in the trap states’ density due to the formation of defects, including the polycrystalline and oxidized amorphous areas in these samples. Furthermore, in a separate set of samples, we varied the shell thickness. We observed that a certain shell thickness of approximately ∼20 nm is needed for efficient passivation of Ga0.31In0.69P nanowires. The photoconductivity of the sample with a shell thickness of 23 nm decays 10 times slower compared with that of the bare core nanowires. We concluded that both the hole and electron trapping and the overall charge recombination in Ga x In(1−x)P nanowires can be substantially passivated through growing an Al y In(1−y)P shell with appropriate Al composition and thickness. Therefore, we have developed an effective in situ surface passivation of Ga x In(1−x)P nanowires by use of Al y In(1−y)P shells, paving the way to high-performance Ga x In(1−x)P nanowires optoelectronic devices.

Al‐neal Degrades Al2O3 Passivation of Silicon Surface

Atomic layer deposited (ALD) aluminum oxide (Al2O3) has emerged as a useful material for silicon devices due to its capability for effective surface passivation and ability to generate p+ region underneath the oxide as active or passive component in semiconductor devices. However, it is uncertain how Al2O3 films tolerate the so‐called Al‐neal treatment that is a necessary process step in devices that also contain silicon dioxide (SiO2) passivation layers. Herein, it is reported that the Al‐neal process is harmful for the passivation performance of Al2O3 causing over eightfold increase in surface recombination velocity (SRV) (from 0.9 to 7.3 cm s−1). Interestingly, it is also observed that the stage at which the so‐called activation of Al2O3 passivation is performed impacts the final degradation strength. The best result is obtained when the activation step is done at the end of the process together with the Al‐neal thermal treatment, which results in SRV of 1.7 cm s−1. The results correlate well with the measured interface defect density, indicating that the Al‐neal affects defects at the Si/SiO x /Al2O3 interface. The root causes for the defect reactions are discussed and possible reasons for the observed phenomena are suggested.

Excitonic characteristics of blue-emitting quantum dot materials in group II-VI using hybrid time-dependent density functional theory

Colloidal quantum dots (QDs) of group II-VI are key ingredients of next-generation QD light-emitting diodes technology for display and lighting, yet the understanding of their luminescent characteristics are far from being mature. Using a hybrid time-dependent density functional theory, we have studied the electronic and excitonic properties of blue-emitting colloidal QDs within group II-VI containing a thousand atoms or more, including CdSe, CdS, ZnSe, and ZnS QDs, considering both quantum confinement and surface ligand effects. It is found that the calculated optical gaps are in excellent quantitative agreement with experiment, irrespective of the QD nature. Scaling laws of size-dependent energy gaps governed solely by quantum confinement effects have further been explored at both single-particle level and correlated excitonic level for all QDs. With concurrently stoichiometric control and enhancing quantum confinement effects, we have predicted an unusual switching of symmetry character of the highest occupied molecular orbital state from a ${\mathrm{\ensuremath{\Gamma}}}_{3}$ to a ${\mathrm{\ensuremath{\Gamma}}}_{1}$ symmetry at ultrasmall size ($\ensuremath{\sim}1$ nm) for all QDs. After the switching, pronounced linearly polarized band-edge excitonic emission is activated. The radiative exciton decay lifetime is found to increase monotonically with increasing the QD size and tends to saturate at larger sizes. Finally, we have explored the surface passivation mechanism of inorganic chloride ligand, and identified various favorable Cd-Cl bonding configurations which enable an effective surface passivation resembling the commonly applied pseudohydrogen passivation scheme. We find that chloride ligand serves as a hole delocalization ligand and tends to redshift the absorption spectra, reduce the absorption intensity, and significantly enhance the exciton decay lifetime. Our results provide a guideline for spectroscopic studies of excitonic characteristics of colloidal QDs within group II-VI.

High-performance CdSe/CdS@ZnO quantum dots enabled by ZnO sol as surface ligands: A novel strategy for improved optical properties and stability

Colloidal semiconductor quantum dots (QDs) have attracted great attention in field of optoelectronic devices. However, the surface organic ligands of QDs involving in optical instability and limited passivation remain challenging, thus bringing additional difficulties in practical application. Here, the high-performance CdSe/CdS@ZnO QDs were successfully prepared by ZnO sol as surface ligands. Importantly, this kind of CdSe/CdS@ZnO QDs maintained the typical advantages of conventional QDs, such as superior monodispersity and long-term storage stability in solution. Because of the effective surface passivation provided by inorganic sol ligands and the deionization effect that electron transferring from surface state of QDs to ZnO acceptor, CdSe/CdS@ZnO QDs showed the remarkably enhanced photostability and biexciton lifetime, as well as further suppressed Auger process and PL blinking. Meanwhile, the CdSe/CdS@ZnO QDs demonstrated PL thermal stability much higher than that of pristine CdSe/CdS QDs under heating to 100 °C, which was efficiently improved 3 times that from ~20% to ~63% of their initial emission intensity. Moreover, a stable amplified spontaneous emission process was observed in CdSe/CdS@ZnO QDs film and still retained a lower ASE threshold (~28 μJ cm−2). Finally, we successfully fabricated a high-performance vertical cavity surface-emitting laser based on CdSe/CdS@ZnO QDs, which presented spatially directional single-mode lasing output with an ultralow threshold of ~3.3 μJ cm−2. We believe that this work could not only enrich the family of surface ligands passivated semiconductor QDs but also provide a novel strategy towards constructing stable and functionalized colloidal nanomaterials for all-inorganic optoelectronic devices.

Understanding the surface passivation effects of Lewis base in perovskite solar cells

Chemical passivation implemented by Lewis base has been demonstrated as an effective method to overcome the water vulnerability of perovskite solar cells (PSCs) along with better performance. Comprehensive understanding of the surface passivation effects is crucial to future improve the PSCs efficiency and stability. Herein, we utilized first-principles to simulate the structure and electronic properties of the passivated perovskite, and carried out ab initio molecular dynamics (AIMD) to understand the effectiveness of the experimental passivation molecules, 2-MP, Py, and PTT, on the classical perovskite (Zhu et al., 2019). Calculations show that introducing both -SH and the N atom of 2-MP enhances the electric dipole moment, the binding strength, the adsorption probability and the carrier transfer rate compared to these of Py and PTT. Moreover, the efficient separation of electrons and holes at the interface and the large bandgap can be achieved by the 2-MP treatment, which is beneficial to improve the photovoltaic performance. AIMD simulations indicate that the interactions of N⋯Pb, S⋯Pb, and H⋯I between 2-MP and the MAPbI3 surface lead to a stronger passivation effect than that of Py and PTT, which is in agreement with the experimental observations. Our results are expected to provide new ideas for developing more distinguished passivation molecules to endow the PSCs stability against water.

Improvement of bifacial heterojunction silicon solar cells with light-trapping asymmetrical bifacial structures

Silicon heterojunction (SHJ) solar cell technology has recently made great progress in mass production. In particular, the average power conversion efficiency (PCE) of mass-produced solar cells has reached nearly 24%. However, the low short-circuit current density (Jsc), a drawback of the SHJ solar cells, has become a bottleneck limiting its further efficiency breakthrough. Therefore, an effective light trapping method is urgently needed for mass-produced SHJ solar cells. In this work, an innovative stacked mask method is developed and combined with a two-step texturing (TST) method to prepare micro-pyramid structures on the front and back side of SHJ solar cells with different pyramid bottom angles, respectively. This asymmetrical structure fabricated through stacked mask method significantly improves the light trapping effect without negative influence on the surface passivation effect. The optical and electrical properties of the SHJ solar cells with this asymmetrical structure under the front side illumination are discussed in detail. It is concluded that the smaller the bottom angle of the backside pyramid, the thinner the amorphous silicon passivation layer is required and the better the surface passivation quality is obtained. The external quantum efficiency (EQE) results demonstrate that the best bottom angle of backside pyramids corresponding to the optimum light trapping effect for the front side illumination is about 16°, which is consistent with the simulation results of the ray tracer. As for the optimal asymmetric structure, the Jsc of the mass-produced SHJ solar cell is improved by 0.36 mA/cm2 and the PCE is increased over 24%.

Unraveling the surface state of photovoltaic perovskite thin film

<h2>Summary</h2> Recently, most of the highly efficient perovskite optoelectronic devices have been reported to employ effective surface passivation strategies, further confirming the significance of surface states in regulating their device performance. Therefore, an in-depth understanding and a systematic approach toward comprehensive investigations on perovskite surface states are urgently required. Here, we present methodical studies toward understanding the surface states in perovskite thin films utilizing a molecular "positively charged defect indicator" strategy. In formamidinium (FA)-methylammonium (MA) mixed-cation perovskite thin films, a nonuniform distribution of cations is uncovered with FA cations being close to the top and MA close to the bottom of the film, which leads to unique surface defect energetics. Antisite FA_I was found to become a dominant deep trap on the surface of this system. As a result, a surface recombination velocity as low as 20 cm/s was achieved in such FA-based perovskite photovoltaic devices.

An Effective Strategy of Combining Surface Passivation and Secondary Grain Growth for Highly Efficient and Stable Perovskite Solar Cells.

Interfacial engineering methods have been developed to solve defect issues of perovskite solar cells (PSCs). However, traditional surface passivation has limited effects on eliminating defect-forming residuals, while secondary grain growth (SGG) is restricted by limited choices of additives and intrinsic properties of perovskites. Here, a pincer strategy of taking advantages of surface passivation and SGG is proposed to modify both exterior and interior of CH3 NH3 PbI3 (MAPbI3 ) perovskite, by employing cyanoacetate-containing donor-acceptor compounds (CA-D-A) including 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylic acid (CA), methanaminium 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAMA), and aminomethaniminium (Z)-2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAFA). In comparison to untreated perovskite, CA-D-A treated perovskites present better crystallinity because of SGG, lower trap densities due to the synergistic effect of surface passivation and SGG, and tuned energy levels induced by CA-D-A. Accordingly, the CA-D-A treated MAPbI3 -based PSCs exhibit higher open-circuit voltage and fill factor than the control PSC without any treatment, leading to improved power conversion efficiency (PCE) and enhanced device stability, especially the CAMA treated PSCs with an average PCE promoted from 17.77 (control PSCs) to 18.71%, and importantly an excellent PCE of 19.71% through further optimization. This work provides an effective strategy for developing highly efficient and stable PSCs with the assistance of both surface passivation and SGG.

First-Principles Study of the Surface Passivation Effect in the Si/MoOx Interface

First-Principles Study of the Surface Passivation Effect in the Si/MoO_<i>x</i> Interface

A Cost‐Effective D‐A‐D Type Hole‐Transport Material Enabling 20% Efficiency Inverted Perovskite Solar Cells†

Main observation and conclusionHigh‐performance, cost‐effective hole‐transport materials (HTMs) are greatly desired for the commercialization of perovskite solar cells (PVSCs). Herein, two new HTMs, TPA‐FO and TPA‐PDO, are devised and synthesized, which have a donor‐acceptor‐donor (D‐A‐D) type molecule design featuring carbonyl group‐functionalized arenes as the acceptor (A) units. The carbonyl group at the central core of HTMs can not only tune frontier molecular orbital (FMO) energy levels and surface wettability, but also can enable efficient surface passivation effects, resulting in reduced recombination loss. When employed as HTMs in inverted PVSCs without using dopant, TPA‐FO with one carbonyl group yields a high power conversion efficiency (PCE) of 20.24%, which is among the highest values reported in the inverted PVSCs with dopant‐free HTMs. More importantly, the facile one‐step synthetic process enables a low cost of 30 USD g–1 for TPA‐FO, much cheaper than the most studied HTMs used for high‐efficiency dopant‐free PVSCs. These results demonstrate the potential of D‐A‐D type molecules with carbonyl group‐functionalized arene core in developing the low‐cost dopant‐free HTMs toward highly efficient PVSCs.

WO3 passivation layer-coated nanostructured TiO2: An efficient defect engineered photoelectrode for dye sensitized solar cell

Major loss factors for photo-generated electrons due to the presence of surface defects in titanium dioxide (TiO2) were controlled by RF-sputtered tungsten trioxide (WO3) passivation. X-ray photoelectron spectroscopy assured the coating of WO3 on the TiO2 nanoparticle layer by showing Ti 2p, W 4f and O 1s characteristic peaks and were further confirmed by X-ray diffraction studies. The coating of WO3 on the TiO2 nanoparticle layer did not affect dye adsorption significantly. Dye sensitized solar cells (DSSCs) fabricated using WO3-coated TiO2 showed an enhancement of ~10% compared to DSSCs fabricated using pristine TiO2-based photo-electrodes. It is attributed to the WO3 passivation on TiO2 that creates an energy barrier which favored photo-electron injection by tunneling but blocked reverse electron recombination pathways towards holes available in highest occupied molecular orbital of the dye molecules. It was further evidenced that there is an optimum thickness (duration of coating) of WO3 to improve the DSSC performance and longer duration of WO3 suppressed photo-electron injection from dye to TiO2 as inferred from the detrimental effect in short circuit current density values. RF-sputtering yields pinhole-free, highly uniform and conformal coating of WO3 onto any area of interest, which can be considered for an effective surface passivation for nanostructured photovoltaic devices.