28.81% efficient, low light intensity and high temperature sustainable ultra-thin IBC solar cell

The interdigitated back contact (IBC) structure for crystalline-silicon photovoltaic device has long been recognized as an effective technique to overcome the 25% efficiency barrier by shifting all the electrical conducting elements to the backside of the cell. For this structure, the architecture of material interlayer IBC electrodes is very important to reduce the recombination rate without affecting the work function at the metal-semiconductor interface for optimum dissolution and extraction of carriers from the absorber layer. Higher efficiency requires a balance between absolute crystal material and impurities in the semiconductor, doping concentration and PN Junctions, smart grid wires and intelligent sunlight capturing. In this work, the fabrication of a low light intensity functional and high cell temperature sustainable, IBC solar cell is investigated. Silicon-Heterojunction layer to absorb greater solar spectrum and interdigitated N/P contacts have been implemented, which grants the cell to receive full surface sunlight, results in 29% efficiency. Luminous-an optoelectronic device simulator has been utilized to construct a very thin cell with dimensions of 100×150pm. The effects of sunlight intensity and module temperature on the performance have been investigated and the parameters for the most efficient structure were found with 28.81% efficiency and 87. 68%fillfactor rate, making it ultra-thin, flexible and durable providing a wide range of operational capabilities

Epitaxial Interdigitated Back Contact (IBC) solar cell test platform for novel light trapping schemes

An Interdigitated Back Contact (IBC) solar cell is being developed for evaluation of emerging light trapping schemes of silicon nanowire arrays on pyramidal textured surfaces. The front surface of the baseline IBC cell design was optimized with a thin film coating considering both antireflection and passivation to reduce surface recombination. Addition of a front surface field (FSF) was shown to improve the surface passivation of the cell. PC2D simulations of the baseline device predict an efficiency of 17.4%. Silicon nanowire arrays and hybrid structures of silicon nanowires on pyramids were successfully fabricated. Hemispherical reflectance measurements show that a weighted average reflectance of just 1.89% was achieved. With adequate surface passivation, these highly-effective antireflective structures could result in a power conversion efficiency increase compared to traditional light trapping methods when incorporated into the IBC cell

Junction formation with HWCVD and TCAD model of an epitaxial back-contact solar cell

In this paper, we present morphological and electrical characteristics of a junction formed of Si p-type films deposited on an n-type silicon wafer using a hot wire chemical vapor deposition (HWCVD) tool. We describe the fabrication process and study the influence of diborane flow and postprocess annealing in improving junction characteristics. Our morphological studies undertaken using atomic force microscopy show that the initial deposition suffered from voids rather than being a uniform film; however, this improves significantly under our annealing treatment. The improvement in morphology was observed in the electrical characteristics, with estimated Voc doubling and rectification of the junction improving by several orders of magnitude. Fitting of the current-voltage curves to a two-diode model showed that increasing the diborane flow in the process helps reduce the saturation current and ideality factors, while increasing the shunt resistance. Electrochemical capacitance-voltage (ECV) and quasi-steady-state photoconductance measurements are used to characterize the deposited films further. A solar cell device with a silicon epitaxy emitter is modeled using industry-standard 3-D modeling tools and input parameters from experimental data, and the impact of defects is studied. A potential efficiency approaching 25% is shown to be feasible for an optimized device

Single mode ridge waveguide using hybrid organic-inorganic sol-gel

Optical waveguides are structures that confine and direct optical signals in a region of higher effective index than its surrounding media. For integrated optics and photonic applications, it is often of importance to prepare waveguides in the form of thin film and channel structures. Hybrid sol-gel material is one of the interesting material in waveguide fabrication as it possess advantages such as low processing temperature, low fabrication cost, and ability of refractive index tuning. Main novelty of this research lies in the development of VTES based optical waveguides. Moreover, refractive index of selected material can be easily tuned by adjusting composition of TTBu in the synthesization stage. Behavior of light propagation and the confinement of light in a hybrid VTES based optical waveguide had been investigated. The characteristics of the waveguide had been simulated by BeamPropTM to obtain the optimum structure for waveguide fabrication. Planar slab waveguides and single mode straight waveguides had been fabricated using low cost photolithographic techniques and wet chemical etching processes. The properties of the hybrid sol-gel material and the fabricated waveguides had been characterized. The experimental results have demonstrated optical waveguiding in the sol-gel material. Attenuation of single mode optical waveguides at 1310 nm and 1550nm with waveguide losses of 1.6dB/cm and 6.7 dB/cm have been obtained respectively. Even though the losses are rather high, the VTES based hybrid sol-gel material is suitable as a waveguiding material in the optical interconnect situations by optimizing the fabrication process

Development of a HWCVD epitaxial IBC solar cell as a test platform for novel antireflection and light trapping schemes

Continuing to reduce the cost-per-watt is the key to providing affordable PV energy. In pursuit of reducing cost-per-watt of silicon PV, this work first focuses on the development of an all back contact silicon solar cell which incorporates a hot wire chemical vapour deposition (HWCVD) technique for p+ emitter deposition. This is as a simpler, lower cost alternative to the traditional high temperature diffusion processes. A proof-of-principle development batch is presented, which resulted in a device with low efficiency, however, through further characterisation, coupled with PC2D device modelling, various potential improvements to the design are identified. A detailed investigation into the as-deposited HWCVD emitter material reveals a polycystalline structure. Post-deposition annealing is shown to improve the crystallinity of the emitter but at the expense of a higher thermal budget. Good diode characteristics are demonstrated for the annealed p-type emitter on an n-type substrate. The focus then shifts to an experimental optimization of the front surface of the cell to achieve a low reflectance and low surface recombination, using conventional methods of thin film coating, pyramidal texturing and front surface field formation. The result is an improved device design and process listing which should result in a high efficiency baseline device on which further optimization can be carried out. A novel front surface antireflection scheme based on a two stage etch process that results in a hybrid nanowire-pyramid surface structure and a weighted average reflectance as low as 1.89% is then described. Conformal coating of the nanowires with alumina using atomic layer deposition is demonstrated, paving the way for effective passivation of these high surface area structures. Finally, a combination of finite difference time domain (FDTD) optical modelling and technology computer aided design (TCAD) electrical simulations predicts that a cell efficiency exceeding 20 % should be possible by combining an optimized HWCVD IBC process with a well-passivated hybrid nanowire-pyramid top surface antireflection scheme

A wirelessly-controlled piezoelectric microvalve for regulated drug delivery

This paper reports a novel wireless control of a normally-closed piezoelectric microvalve activated by a wireless inductor-capacitor (LC) resonant circuit, and enabled by an external magnetic field. The LC circuit is formed by connecting a multilayer coil to a piezoelectric actuator (PEA) that behaves as a capacitor and a resistor in parallel. The LC circuit is activated by modulating the field frequency to its resonant frequency (fr) of 10 kHz, which matches the optimal operating frequency of the device, while considering the resonant frequency of the PEA. The working fluid is stored in an 88.9 μL polydimethylsiloxane balloon reservoir that pumps the liquid due to the difference in pressure, which eliminates the need for a pump. The design of the device was optimized using several analytical and experimental approaches. This device was fabricated using a time and cost-effective out-of-clean-room fabrication process. The valving performance was initially characterized in air, then in phosphate buffered saline (PBS) solution to mimic the drug release kinetics into human interstitial body fluids. Maximum flow rate values of 8.91 and 7.42 μL/min are achieved in air and PBS solution respectively, at a maximum input pressure value of ∼13 kPa. A programmed short-term delivery of desired liquid volumes in separate batches shows that the volumes are delivered into air and PBS solution with maximum percentage errors of 7.49% and 7.91%, respectively. Additionally, a programmed 3-day long-term reliability test shows that the device was able to achieve desired flow rate values between 160 and 320 μL/day in air and PBS solution with a maximum percentage error of 3.11% and 4.39%, respectively. The results show that the developed device has high potential to be used in drug delivery applications

Passivation of all-angle black surfaces for silicon solar cells

Optical losses at the front surface of a silicon solar cell have a significant impact on efficiency, and as such, efforts to reduce reflection are necessary. In this work, a method to fabricate and passivate nanowire-pyramid hybrid structures formed on a silicon surface via wet chemical processing is presented. These high surface area structures can be utilised on the front surface of back contact silicon solar cells to maximise light absorption therein. Hemispherical reflectivity under varying incident angles is measured to study the optical enhancement conferred by these structures. The significant reduction in reflectivity (<2%) under low incident angles is maintained at high angles by the hybrid textured surface compared to surfaces textured with nanowires or pyramids alone. Finite Difference Time Domain simulations of these dual micro-nanoscale surfaces under varying angles supports the experimental results. In order to translate the optical benefit of these high surface area structures into improvements in device efficiency, they must also be well passivated. To this end, atomic layer deposition of alumina is used to reduce surface recombination velocities of these ultra-black silicon surfaces to below 30 cm/s. A decomposition of the passivation components is performed using capacitance-voltage and Kelvin Probe measurements. Finally, device simulations show power conversion efficiencies exceeding 21% are possible when using these ultra-black Si surfaces for the front surface of back contact silicon solar cell

Junction properties analysis of silicon back-to-back Schottky diode with reduced graphene oxide Schottky electrodes

Reduced graphene oxide (rGO)/silicon (Si) Schottky junction possesses promising attributes for various applications such as chemical sensor and photodetector. In this paper, a fabrication of simple back-to-back rGO/Si Schottky junction structure is presented. The device was fabricated via wet processes such as vacuum filtration, patterning by delamination, wet transfer and chemical reduction by ascorbic acid. From the current-voltage measurement, series resistance, barrier height and ideality factor were investigated at different temperature. Barrier height increases and ideality factor decreases with the increase of temperature indicating the inhomogeneity of the junction interface. By considering the Gaussian distribution of barrier height, the fabricated Schottky junction was shown to possess the mean barrier height of 1.24 eV with standard deviation value of 0.16 eV. The obtained mean barrier height was larger than the bandgap of Si, indicating the presence of thin insulation layer at the interface