Backside Illumination Research Articles

Bilayer TiO2/Mo-BiVO4 Photoelectrocatalysts for Ibuprofen Degradation

Heterojunction formation between BiVO4 nanomaterials and benchmark semiconductor photocatalysts has been keenly pursued as a promising approach to improve charge transport and charge separation via interfacial electron transfer for the photoelectrocatalytic degradation of recalcitrant pharmaceutical pollutants. In this work, a heterostructured TiO2/Mo-BiVO4 bilayer photoanode was fabricated by the deposition of a mesoporous TiO2 overlayer using the benchmark P25 titania catalyst on top of Mo-doped BiVO4 inverse opal films as the supporting layer, which intrinsically absorbs visible light below 490 nm, while offering improved charge transport. A porous P25/Mo-BiVO4 bilayer structure was produced from the densification of the inverse opal underlayer after post-thermal annealing, which was evaluated on photocurrent generation in aqueous electrolyte and the photoelectrocatalytic degradation of the refractory anti-inflammatory drug ibuprofen under back-side illumination by visible and UV–Vis light. Significantly enhanced photoelectrochemical performance on both photocurrent density and pharmaceutical degradation was achieved for the bilayer structure with respect to the additive effect of the constituent layers, which was related to the improved light harvesting arising from the backscattering by the mesoporous TiO2 layer in combination with the favorable charge transfer at the TiO2/Mo-BiVO4 interface.

Hybrid CIGS‐Cobalt Quaterpyridine Photocathode with Backside Illumination: a New Paradigm for Solar Fuel Production

Chalcogenide‐based thin‐film solar cell optimized for rear illumination and used for CO2 reduction is presented. Central to this innovation is a thinner, Cu(In,Ga)S2 chalcopyrite absorber coated with a robust metallic top layer, which potentially surpasses the performance of conventional front‐illuminated designs. Using cobalt quaterpyridine molecular catalyst, photocurrent densities for CO2 reduction exceeding 10 mA/cm2 at 0.0 V vs. RHE under 1 Sun illumination, and ca. 16 mA/cm2 at ‐0.25 V vs. RHE were achieved in voltammetry experiments. Controlled potential electrolysis showed catalytic activity over 20 h with selectivity for CO ranging from > 92% (first 4 hours) to 86% at the end of the experiment. This approach opens limitless possibilities for employing various reduction catalysts, extending far beyond CO2 reduction. It imposes minimal constraints on absorption properties, immobilization methods, and catalyst nature, setting the stage for high‐performance, adaptable PEC devices.

Numerical evaluation of bi-facial ZnO/MoTe2 photovoltaic solar cells with N-doped Cu2O as the BSF layer for enhancing V OC via device simulation.

Molybdenum telluride (MoTe2) shows great promise as a solar absorber material for photovoltaic (PV) cells owing to its wide absorption range, adjustable bandgap, and lack of dangling bonds at the surface. In this research, a basic device structure comprising Pt/MoTe2/ZnO/ITO/Al was developed, and its potential was assessed using the SCAPS-1D software. The preliminary device exhibited a photovoltaic efficiency of 23.87%. The integration of a 100 nm thick nitrogen-doped copper oxide (N-doped Cu2O) layer as a hole transport/BSF layer improved the device performance of the MoTe2/ZnO photovoltaic solar cell (PVSC), increasing the open circuit voltage (V OC) from 0.68 V to 1.00 V and, consequently, its efficiency from 23.87% to 34.45%. Recombination and C-V analyses were conducted across various regions of the device with and without the BSF layer. The results of these analyses revealed that this improvement in the device performance mainly stemmed from a decrease in recombination losses at the absorber/BSF interface and an increase in the built-in potential of the device, resulting in improved V OC and photovoltaic efficiency. Additionally, the performance of the device in a bifacial mode was studied. The calculated bifacial factor (BF) values suggested that there were negligible additional losses affecting some parameters when the solar cell was under backside illumination and emphasized the potential for improved energy harvest in bifacial solar cells without significant drawbacks.

Effect of physical vapor deposition on contacts to 2D MoS2

Two-dimensional (2D) molybdenum disulfide (MoS2) holds immense promise for next-generation electronic applications. However, the role of contact deposition at the metal/semiconductor interface remains a critical factor influencing device performance. This study investigates the impact of different metal deposition techniques, specifically electron-beam evaporation and sputtering, for depositing Cu, Pd, Bi, Sn, Pt, and In. Utilizing Raman spectroscopy with backside illumination, we observe changes at the buried metal/1L MoS2 interface after metal deposition. Sputter deposition causes more damage to monolayer MoS2 than electron-beam evaporation, as indicated by partial or complete disappearance of first-order E′(Γ)α and A′1(Γ)α Raman modes post-deposition. We correlated the degree of damage from sputtered atoms to the cohesive energies of the sputtered material. Through fabrication and testing of field-effect transistors, we demonstrate that electron-beam evaporated Sn/Au contacts exhibit superior performance including reduced contact resistance (~12×), enhanced mobility (~4.3×), and lower subthreshold slope (~0.6×) compared to their sputtered counterparts. Our findings underscore the importance of contact fabrication methods for optimizing the performance of 2D MoS2 devices and the value of Raman spectroscopy with backside illumination for gaining insight into contact performance.

High performance Bi-facial dye sensitized solar cells developed using MXenes assisted novel photoelectrode design

A new device architecture of bi-facial dye sensitized solar cell (DSSC) is designed, fabricated by use of novel photoelectrode design contains MXenes. The developed bi-facial DSSC witnessed higher power conversion efficiency (PCE) of 12.82 % with short-circuit current density (JSC) of 27.46 mA/cm2. The DSSC revealed 9.74 % of PCE by front side illumination and 4.57 % by back side illuminations. The results motivated to develop mini-module of series connected 12 test cells, which results in 13.34 % of PCE.

High sensitivity cameras can lower spatial resolution in high-resolution optical microscopy

High-resolution optical fluorescence microscopies and, in particular, super-resolution fluorescence microscopy, are rapidly adopting highly sensitive cameras as their preferred photodetectors. Camera-based parallel detection facilitates high-speed live cell imaging with the highest spatial resolution. Here, we show that the drive to use ever more sensitive, photon-counting image sensors in cameras can, however, have detrimental effects on the spatial resolution of the resulting images. This is particularly noticeable in applications that demand a high space-bandwidth product, where the image magnification is close to the Nyquist sampling limit of the sensor. Most scientists will often select image sensors based on parameters such as pixel size, quantum efficiency, signal-to-noise performance, dynamic range, and frame rate of the sensor. A parameter that is, however, typically overlooked is the sensor’s modulation transfer function (MTF). We have determined the wavelength-specific MTF of front- and back-illuminated image sensors and evaluated how it affects the spatial resolution that can be achieved in high-resolution fluorescence microscopy modalities. We find significant differences in image sensor performance that cause the resulting spatial resolution to vary by up to 28%. This result shows that the choice of image sensor has a significant impact on the imaging performance of all camera-based optical microscopy modalities.

Near‐Infrared Imaging Highly Enhanced by Pixel‐Level Integrated Plasmonic Metasurfaces on CMOS Image Sensors

AbstractNear‐infrared (NIR) photodetection and imaging have sparked significant interests across a wide range of applications. While silicon photodiodes are commonly employed, the small light absorption coefficients of Si in NIR severely limit the performance, especially in the case of thin active Si layers. Although various light harvesting techniques are proposed to increase light absorption of Si, pixel‐level strategy for enhanced NIR imaging is still challenging in CMOS image sensors (CISs) with a pixel size in only a micron scale. In this paper, plasmonic metasurfaces are intimately integrated on top of 2.3 µm thick Si active regions of the pixels of a backside illumination (BI)‐CIS for NIR imaging for the first time. 200% improved photoresponsivity is obtained in experiments in such a planar Si layer rather than patterning the Si layer with potential damage to the active region. Numerical simulation results reveal highly enhanced light intensity in the thin active Si layer due to the presence of plasmonic metasurfaces. Significantly improved imaging brightness and signal‐to‐noise ratio of NIR imaging are demonstrated under both laser and LED illumination. This CMOS‐compatible technique is expected to hold promising potentials in applications including machine vision, iris certification, light detection and ranging (LiDAR), and optical communication in data centers.

Fresnel Diffraction Model for Laser Dazzling Spots of Complementary Metal Oxide Semiconductor Cameras.

Laser dazzling on complementary metal oxide semiconductor (CMOS) image sensors is an effective method in optoelectronic countermeasures. However, previous research mainly focused on the laser dazzling under far fields, with limited studies on situations that the far-field conditions were not satisfied. In this paper, we established a Fresnel diffraction model of laser dazzling on a CMOS by combining experiments and simulations. We calculated that the laser power density and the area of saturated pixels on the detector exhibit a linear relationship with a slope of 0.64 in a log-log plot. In the experiment, we found that the back side illumination (BSI-CMOS) matched the simulations, with an error margin of 3%, while the front side illumination (FSI-CMOS) slightly mismatched the simulations, with an error margin of 14%. We also found that the full-screen saturation threshold for the BSI-CMOS was 25% higher than the FSI-CMOS. Our work demonstrates the applicability of the Fresnel diffraction model for BSI-CMOS, which provides a valuable reference for studying laser dazzling.

Photocatalytic oxidation of n-decane in a NETmix photoreactor: Insights into the reactor geometry and illumination mechanism

This study focuses on the gas-phase photocatalytic degradation of n-decane using a NETmix photoreactor illuminated by UVA light-emitting diodes. The photoreactor is a static mixer composed of a network of cylindrical chambers interconnected by prismatic channels imprinted in a stainless-steel slab sealed with a borosilicate glass slab (reactor window with 55.7 cm2 of illuminated area). Photocatalytic performance was evaluated as a function of the flow rate (0.67 to 15 L min−1), corresponding to Reynolds number (Re) from 54 to 1209, using NETmix plates with 1 mm (92.3 cm2) and 3 mm depth (165.4 cm2), under back-side (BSI) and front-side (FSI) illumination mechanisms. The TiO2-P25 loading over the borosilicate slab (25–100 mg; BSI optimal: 75 mg) and stainless-steel slabs (100–400 mg; FSI-1/FSI-3 optimal: 200/400 mg) was optimized. Within system constraints, higher Re corresponds to increased reaction rate, apparent quantum yield, and reactivity, with decreased degradation efficiency, due to a reduction in the residence time, regardless of the reactor geometry and illumination. Moreover, operating at the same Re, the NETmix plate with 3 mm depth achieves reaction rates 2.2-/1.9-fold higher than 1 mm, considering FSI/BSI mechanisms. The results were consistent with applied experimental conditions and ray tracing simulations, indicating superior kinetic performance with higher catalyst superficial area. Ray tracing was coupled with Computational Fluid Dynamics (CFD) simulations to evaluate n-decane single-pass oxidation. A 94 % n-decane maximum experimental conversion was attained for a Re of 54, representing an error of ∼ 6.6 % compared to CFD simulation. In these conditions, only 1 % of n-decane was not mineralized, being identified aldehydes, alkanes, carboxylic acids, and ketones as the main reaction by-products. The influence of relative humidity (2 %-40 %) and n-decane inlet concentration (15–114 ppm) were also investigated.

Coupling Cuprous Oxide with Upconversion Materials: A Holistic Approach to Efficient Solar Water Splitting

Photoelectrochemical (PEC) water splitting is a promising solution for harnessing solar radiation for hydrogen production. This technology combines sunlight capture and water electrolysis processes, resulting in the production of hydrogen and oxygen that can efficiently recombine in fuel cells. However, challenges in materials science still need resolution to establish PEC water splitting as a practical and competitive approach. Copper oxide semiconductors, particularly materials based on cuprous oxide (Cu2O), have attracted attention due to their abundant elemental availability, scalable synthesis methods, and inherent p-type characteristics. To improve the generated photocurrent of the photoelectrode system, photon upconversion (UC) materials can be implemented into water-splitting devices. TTA-based UC is particularly suitable for solar water splitting due to its efficient conversion at low photon intensity. This work highlights the potential application of TTA-based UC in solar-assisted water splitting and highlights the significance of photonic designs and nanointerface engineering to improve the light-harnessing properties of photoactive materials. To the best of our knowledge, our research group was the first to successfully implement the integration of photoactive materials for solar water splitting with an upconversion device based on the TTA mechanism. This strategy allows us to dramatically improve the light-harnessing properties of our photoelectrode by irradiating the photocatalyst from dual perspectives (front and back-side illumination). It has been demonstrated that Cu2O coupled with an upconverter (UC) outperforms bare Cu2O by 56% in terms of produced photocurrent density, namely bare Cu2O produces -0.32 mA·cm-2 at 0V (vs. RHE), whereas Cu2O/UC exhibits a photocurrent of -0.5 mA·cm-2. Figure 1

Effects of Al2O3 Rear Interface Passivation on the Performance of Bifacial Kesterite‐Based Solar Cells with Fluorine‐Doped Tin Dioxide Back Contact

Herein, ultrathin Al2O3 is investigated as a rear interface passivation layer for kesterite solar cells with F:SnO2 (FTO) back contact for potential performance improvement. On the passivation layer, a thin Mo layer is deposited to improve the FTO's ohmicity. Further, NaF is evaporated on the copper zinc tin sulfide (CZTS) precursors to create openings at the passivation layer and achieve Na‐induced benefits in the absorber. The CZTS absorbers deposited directly on the Al2O3‐coated FTO peel off, while those with Mo interlayer do not. For pure sulfide kesterite devices, the Al2O3 layer reduces the short‐circuit current density (JSC), resulting in poor device efficiency. On the other hand, significantly higher JSC is realized for mixed sulfide and selenide kesterite devices with Al2O3 passivation layer, with the current density–voltage curve suggesting a reduced barrier height at the rear interface. As a result, the efficiency is improved from 1.5% for devices without Al2O3 to 4.6% for those with Al2O3. Likewise, improved external quantum efficiency response is observed in the devices with passivation layer for backside and frontside illumination. Therefore, contribution of Al2O3 passivation layer to the performance of kesterite‐based solar cells is evident from the results of this study.

Hybrid Organic-Si C-MOSFET Image Sensor Designed with Blue-, Green-, and Red-Sensitive Organic Photodiodes on Si C-MOSFET-Based Photo Signal Sensor Circuit.

The resolution of Si complementary metal-oxide-semiconductor field-effect transistor (C-MOSFET) image sensors (CISs) has been intensively enhanced to follow the technological revolution of smartphones, AI devices, autonomous cars, robots, and drones, approaching the physical and material limits of a resolution increase in conventional Si CISs because of the low quantum efficiency (i.e., ~40%) and aperture ratio (i.e., ~60%). As a novel solution, a hybrid organic-Si image sensor was developed by implementing B, G, and R organic photodiodes on four n-MOSFETs for photocurrent sensing. Photosensitive organic donor and acceptor materials were designed with cost-effective small molecules, i.e., the B, G, and R donor and acceptor small molecules were Coumarin6 and C_60, DMQA and MePTC, and ZnPc and TiOPc, respectively. The output voltage sensing margins (i.e., photocurrent signal difference) of the hybrid organic-Si B, G, and R image sensor pixels presented results 17, 11, and 37% higher than those of conventional Si CISs. In addition, the hybrid organic-Si B, G, and R image sensor pixels could achieve an ideal aperture ratio (i.e., ~100%) compared with a Si CIS pixel using the backside illumination process (i.e., ~60%). Moreover, they may display a lower fabrication cost than image sensors because of the simple image sensor structure (i.e., hybrid organic-Si photodiode with four n-MOSFETs).

Hierarchical Transparent Back Contacts for Bifacial CdTe PV.

A hierarchical transparent back contact leveraging an AlGaOx passivating layer, Ti3C2Tx MXene with a high work function, and a transparent cracked film lithography (CFL) templated nanogrid is demonstrated on copper-free cadmium telluride (CdTe) devices. AlGaOx improves device open-circuit voltage but reduces the fill factor when using a CFL-templated metal contact. Including a Ti3C2Tx interlayer improves the fill factor, lowers detrimental Schottky barriers, and enables metallization with CFL by providing transverse conduction into the nanogrid. The bifacial performance of an AlGaOx/Ti3C2Tx/CFL gold contact is evaluated, reaching 19.5% frontside efficiency and 2.8% backside efficiency under 1-sun illumination for a copper-free, group-V doped CdTe device. Under dual illumination, device power generation reached 200 W/m2 with 0.1 sun backside illumination.

Toward improving the performance of Cu2ZnSnS4-based solar cells with Zr, W or sulfurized layers at the SnO2:F/Cu2ZnSnS4 rear interface

The photovoltaic performance of Cu2ZnSnS4 (CZTS)-based thin film solar cells with transparent back contacts is mainly constrained by the ohmic loss due to degradation of the back contacts at high temperatures required for the growth of the CZTS absorbers. This work has attempted to use ultrathin Zr and W interlayers at the SnO2:F (FTO)/CZTS interface with the purpose of improving the ohmic properties of FTO and hence the performance of solar cells. 20 nm thick Zr and W layers were coated on FTO using direct current magnetron sputtering, followed by heating at 550 °C in a sulfur atmosphere for some of the samples. Inclusion of Zr and W interlayers compromised the transmittance of the FTO back contact, however heating of the samples in a sulfur atmosphere improved the transmittance to values comparable to or better than those of un-heated FTO. Furthermore, heated W/FTO showed a significant improvement in electrical conductivity as observed from Hall effect measurements. To make complete solar cells, CZTS absorber, buffer (CdS) and window (i-ZnO/ZnO:Al) layers were sequentially deposited on the un-heated FTO, Zr/FTO, W/FTO and Mo back contacts. Glow discharge optical emmision spectroscopy confirmed that Zr and W did not diffuse into the absorber and also prevented Na diffusion into the absorber. From the scanning electron microscopy cross sectional analysis, an impovement in the absober grain size and a clear junction between the absorber and FTO with W interlayer were observed. Grazing incident X-ray diffractometry confirmed the polycrystalline nature of the CZTS thin films and indicated the presence of other phases, particularly SnS2. On the resulting solar cell parameters, the inclusion of a W interlayer reduced the series resistance from 4.5 Ωcm to 3.7 Ωcm2. An improvement in short circuit current density (JSC) is also observed, enhancing the efficiency of the solar cells with CZTS/W/FTO to 3.1 % compared to that with CZTS/Mo at 2.7 % and CZTS/FTO at 3.0 %. W was found to improve the external quantum efficiency response and JSC of the solar cells for both backside and frontside light illumination. On the other hand, inclusion of a Zr interlayer (Zr/FTO) only slighlty improved the open circuit voltage, but compromised the JSC compared to FTO and W/FTO back contacts. Thus, the findings of this study demonstrate the prospect for improving the performance of the CZTS-based thin film solar cells through the inclusion of ultrathin Zr and W interlayers between the FTO back contact and CZTS absorber.

Ultrahigh-speed imaging for high-impact concrete deformation analysis in pre- and post-cracking stages.

The evaluation of high-speed camera image sequence analysis results in concrete material testing under high-impact loading necessitates the consideration of the effect of the image quality on the measurement accuracy and thus on the potential of the geometric measurements derived from the image sequences. In this contribution, we evaluate the application potential of three ultrahigh-speed cameras with frame rates up to 10Mfps to analyze the deformation of concrete specimens before and after main crack formation in bending and compression tests. Specifically, we evaluate the Kirana 7M and Shimadzu HPV-X2 cameras with ISIS sensor architecture, and the Phantom TMX 7510 camera with BSI CMOS sensor technology. Three-point bending tests and split-Hopkinson pressure bar tests are performed on 160×40×40m m 3 cuboids and on 80mm long, 50mm diameter cylinders. Prior to main crack formation, the displacement vector field represents the specimen deformation, with higher values indicating the position where main cracks will initiate and propagate. Deformations of 80µm in 54µs for a bending test and of 154µm in 36.67µs for a compression test could be measured. The main cracks are then detected using displacement vector field discontinuity analysis techniques, and their evolution is followed to estimate the crack propagation velocity. Average velocities in bending tests between 603 and 854m/s have been determined over a time interval up to 40µs. An investigation of the camera sensor operation of the three optical devices is presented to assess their suitability for deformation analysis. Laboratory tests and real experimental results show that the quality of the propagation vector field, the crack detection, and the crack tip tracking are obviously affected by the image quality, but more significantly by the spatial and temporal resolution due to the small relative step deformations.

Towards a Better Understanding of the Back-Side Illumination Mode on Photocatalytic Metal–Organic Chemical Vapour Deposition Coatings Used for Treating Wastewater Polluted by Pesticides

Pesticides are emerging contaminants that pose various risks to human health and aquatic ecosystems. In this work, diuron was considered as a contaminant model to investigate the influence of the back-side illumination mode (BSI) on the photocatalytic activity of TiO2 coatings grown on Pyrex plates by metal–organic chemical vapour deposition (MOCVD). A photoreactor working in recirculation mode was irradiated at 365 nm with ultraviolet A (UVA) light-emitting diodes in BSI. The degradation of diuron and its transformation products was analysed by high-performance liquid chromatography, ion chromatography, and total organic carbon analysis. The coatings were characterised by X-ray diffraction analysis and scanning electron microscopy. Five coatings containing 3, 7, 10, 12 and 27 mg of TiO2 exhibited different morphology, crystallinity, thickness and photocatalytic activities. The morphology and crystallinity of the coatings had no significant influence on their photocatalytic activity, unlike their mass and thickness. TiO2 contents less than 10 mg limit the photocatalytic activity, whereas those greater than 15 mg are inefficient in the BSI because of their thickness. The maximum efficiency was achieved for coatings of thickness 1.8 and 2 µm with TiO2 contents of 10 and 12 mg, revealing that the photocatalyst thickness controls the photocatalytic efficiency in the BSI.

Photo-Imageable Dielectrics Enabling Structured MEMS and 2.5D / 3D Bonding Systems

DuPont has developed a new Photo-Imageable Dielectric (PID) to complement its existing permanent bonding materials. The CYCLOTENEâ?¢ family of dielectric materials are well known for use as a permanent dielectric and have seen significant use in commercial applications including BSI CMOS image sensors, integrated passive devices and as an optical bonding adhesive. For new applications, there is a desire to have a thermal stable material that can be patterned to eliminate the material from the metal joining region or from the light path. We will demonstrate in this paper that the solvent developed PID as well as our existing aqueous developable PID are both capable of wafer to wafer bonding after photo imaging and development. In addition to bonding using a commercial wafer to wafer bonding tool, we have shown that wafer to wafer bonding is achievable using a two-stage vacuum laminator. Optimization of the curing process will be discussed to prevent any separation or reflow of the PID as well as achieving the maximum adhesion energy after full cure. Finally, we will show the use of the negative tone PID as a solder collar or polymer dam to enable high density flip chip bonding using 15?m Sn/Ag capped copper pillars with a 1:1.5 pitch to a and 18?m polymer openings with a 1:1.08 pitch in 10mm x 10mm dies as well as outline the process we will use to extend this approach to Cu-Cu hybrid bonding.

Automatic Classification of C-SAM Voids for Root Cause Identification of Bonding Yield Degradation

Wafer-level direct bonding technology is a key process for the production of backside illuminated (BSI) CMOS image sensor (CIS). Usually, constant-depth mode scanning acoustic microscope (C-SAM) 300mm wafer images are acquired and defect size distribution is provided to monitor defects that degrade bonding yield. This acquisition technique is used as it is nondestructive and is able to capture the full wafer. Current solutions are not providing information detailed enough to identify the root cause of this degradation. A consequence is that most measurements and classification is currently done manually which take time and have reproducibility issues. In this paper, we propose a rule-based method for the classification of the defects and automatic segmentation of the defects to extract precise measurements depending on the type of defect. The classes of defects are precisely defined based on their origin in the process. All these information will allow to reduce the time to analyze the images and improve the precision and consistency of the analysis. These results will allow to identify more precisely the defects thus the causes of yield degradation during bonding process.

Enhanced performance of Cu2ZnSnS4 based bifacial solar cells with FTO and W/FTO back contacts through absorber air annealing and Na incorporation

This study reports on the influence of air annealing and Na incorporation into the absorber on the performance of Cu2ZnSnS4 (CZTS) bifacial solar cells with FTO and W/FTO back contacts. Na was incorporated by depositing ∼12 nm thick NaF on the CZTS precursors prior to the sulfurization process via thermal evaporation. After sulfurization, some of the samples were annealed in air at 300 °C for 90 s and subsequently at 200 °C for 600 s. Transmission electron microscopy confirmed sulfurization of the W interlayer to form WS2 which improves the FTO ohmicity. Na incorporation improved grain size of the absorber as revealed by scanning electron microscopy. Non-annealed samples had the unwanted SnS2 phase while the air annealed samples, particularly those with both W interlayer and Na incorporation, were exempt from SnS2 phase, as was confirmed through grazing incident X-ray diffraction and Raman spectroscopy. These results suggest that absorber air annealing and Na incorporation enhance absorber crystal growth which is advantageous in reducing bulk carrier recombination. As a result, the efficiency was significantly improved from 3.0% for solar cells fabricated directly on FTO to 5.2% for those whose absorbers were air annealed, incorporated with Na and made on W/FTO. The latter also exhibits the highest external quantum efficiency response and calculated short circuit current density for both sides illumination. This indicates that the air annealing, Na incorporation and W interlayer are enhancing the performance of bifacial CZTS solar cells with FTO back contact for both back side and front side illumination.

Enabling real-time detection of photocatalytic reactions by a re-useable micro-reactor

We present a highly sensitive and versatile Si-based μ-reactor for photocatalytic experiments. The μ-reactor can be operated in front side (through a borosilicate window) as well as backside (through the catalyst support) illumination. The μ-reactor is sealed by compressing the Si-based microchip, a parafilm gasket and the supported catalyst by four screws. This design allows for fast and reliable assembly of the μ-reactor and the microchip is re-usable for several independent experiments, making the presented μ-reactor ideal for catalyst screening studies. We analyze volatile reactants on-line by connecting the μ-reactor to a mass-spectrometer. The limiting capillary of the μ-reactor allows for nearly 100% collection efficiency (i.e. every produced molecule will be collected) by limiting the gas flow to the mass-spectrometer—enabling highly sensitive measurements and an absolute calibration. Finally, the small height of the reactor volume results in very fast response times, which make the reactor suitable for studies of transient activity phenomena—including catalyst activation and deactivation. We demonstrate these capabilities of the μ-reactor by performing CO oxidation experiments on a TiO2 thin film with subsequent calibration of the chip. Based on a mathematical model of the μ-reactor we additionally present a method for determining the residence time, the reaction volume and the working distance.