Diode Injection Current Research Articles

A Framework for Process-to-Module Modeling of a-Si/c-Si (HIT) Heterojunction Solar Cells to Investigate the Cell-to-Module Efficiency Gap

The cell-to-module efficiency gap observed in a-Si/c-Si heterojunction solar cells is a key challenge to the broad adoption of this technology. To systematically address this issue, we describe an end-to-end modeling framework to explore the implications of process and device variations at the module level. First, a process model is developed to connect the a-Si deposition parameters to the material properties. Next, a physics-based device model is presented; the model uses the thermionic emission/diffusion theory to capture the essential features of photocurrent and diode injection current. Using the process and device models, the effects of process conditions on cell performance are explored. Finally, the performance of the module, as a function of device and process parameters, is explored to establish the cell-to-module efficiency gap. The insights developed through this process-to-module modeling framework will help close the cell-to-module efficiency gap of this commercially promising technology.

The Frozen Potential Approach to Separate the Photocurrent and Diode Injection Current in Solar Cells

The principle of superposition is commonly utilized in the analysis of current transport under dark and light conditions for several different types of solar cells. However, this principle assumes that the photocurrent is voltage independent and that the diode injection current is generation independent, which restricts its validity. Indeed, the superposition principle cannot be applied to most thin-film solar cells because the above mentioned assumptions are not generally valid. In order to address this issue, a novel numerical modeling approach is described that allows independent computation of the photocurrent and of the diode injection current as components of the total current under illumination. Then, using several test cases, where the principle of superposition breaks down, the usefulness of this modeling approach is demonstrated.

An external cavity diode laser using a volume holographic grating

This study presents an external cavity diode laser (ECDL) system, utilizing a volume holographic grating (VHG) and a microfabricated silicon flexure as the VHG holder. The laser design is aimed for easy assembly, controllability, and better stability of the laser cavity. The laser frequency was stabilized to a D2 transition of rubidium at 780.247nm, with a mode-hop-free tuning range of 16GHz and 9.6GHz with and without feed-forward on the diode injection current. The measured linewidth was 850kHz in 500s, qualified for laser cooling experiments.

Analysis of quasi-distributed optical sensors combining rf modulation with the FMCW method

We report the theoretical analysis of a quasi-distributed sen- sor system for absorption measurements based on the frequency- modulated continuous wave (FMCW) technique combined with fre- quency modulation spectroscopy (FMS). The laser diode injection current is sawtooth modulated to provide a linear scan of the output over a certain frequency/wavelength range and the output is also externally modulated at radio frequencies. The sensor units consist of a series of open-path micro-optic cells constructed from graded index (GRIN) lenses, each with a unique beat frequency. By arranging for only one sideband of the modulation to be attenuated by the absorption feature, a new signal, proportional to the absorbance, appears in the output spec- trum at a frequency corresponding to the difference between the rf- modulation frequency and the beat frequency of a cell. The method is highly sensitive and applicable to a variety of chemical species with nar- row absorption lines, such as in trace gas analysis. We present the mathematical analysis of the proposed method for single and multiple

Timing-jitter reduction of a mode-locked Cr:LiSAF laser by simultaneous control of cavity length and pump power

The pulse-repetition frequency of a mode-locked Cr:LiSAF laser has been stabilized to an electrical reference signal by simultaneous control of the laser cavity length and the pump power. The phase difference between the laser pulse and an electrical reference signal is detected by use of a digital phase detector and fed back to a piezoelectric transducer and to a laser diode injection current. A rms timing jitter of 7.5 fs relative to the reference was obtained for the 25-mHz-10-kHz bandwidth.

A novel high-resolution interference spectrometer

A novel precision wavemeter is presented with a resolution of better than 0·01 nm. A Sagnac interferometer with two diffraction gratings forms the basis of the instrument. Using spatial heterodyning techniques and a CCD camera/frame grabber data acquisition system allows fast computer control and power spectrum analysis. The mode structure and mode hopping characteristics of a typical laser diode were examined as a function of diode injection current.

Multipass Michelson interferometer with the use of a wavelength-modulated laser diode

An improved multipass Michelson interferometer is implemented. This technique uses the fact that the wavelength of a laser diode varies in proportion to the diode's injection current. With this method the sensitivity augmentation is accomplished by inserting a beam splitter into one arm of the interferometer, resulting in multiple reflections between the end mirror and the beam splitter. In addition, the interference of laser beams reflected from two arms can be accomplished with unequal arms in the condition of a short coherence length. The sensitivity increase of interference fringes and the compensation of the short coherence length have been demonstrated in experiments.

Range finding and velocimetry with directional discrimination using a modulated laser diode Michelson interferometer

A dynamic laser interferometer for ranging and velocity measurements using a modulated laser diode as light source in an unbalanced Michelson configuration is described. The technique uses the fact that the wavelength of the emitted light varies linearly with the injection current. When the diode's injection current is modulated in a triangular wave, a heterodyne beat signal is generated with a frequency proportional to the optical path difference. When the target is moving, the technique allows absolute distance measurement with directional discrimination as well as target velocity. The device is described and experimental results are presented.