Moustafa Ghannam

Simple integral screenprinting process for selective emitter polycrystalline silicon solar-cells

This letter describes a new simple fabrication process, developed recently for ‘‘blue response’’ improvement in low‐cost polycrystalline silicon solar cells. A selective emitter is created by heavily doping the emitter, followed by a wet etching‐back of the cell area between the fingers. An improvement up to 17 mV in Voc, 1.5 mA/cm2 in Jsc, and 1% (absolute value) in η is obtained. Effective phosphorus gettering, self‐alignment, and application in a low‐cost full screenprinting technology are the main advantages of the proposed process.

An analytical model for the determination of the transient response of CML and ECL gates

In the analysis, the full-range transient response of the gate is calculated using closed-form analytical expressions. This is achieved by generalizing and improving the method used by J.M.C. Stork (IEDM Tech. Dig., p.550, 1988) for the determination of the propagation delay. The proposed model is applicable at low-level injection, unity fan-in, and unity fan-out. The delays related to the transit time, the load, and the junction capacitances are considered. For ECL gates, the emitter follower delay is also included. Various delays (risetime, propagation delay, etc.) calculated using the proposed model agree perfectly with the results of SPICE computer simulations and with the reported experimental values. >

Surface recombination current with a nonideality factor greater than 2

It is shown both theoretically and experimentally that under inverted surface conditions the surface recombination current of a bipolar transistor has an exponential nonideality factor >2. The behavior of the surface recombination current follows closely that of the excess leakage current in stressed-self-aligned silicon bipolar transistors at forward bias.<<ETX>>

Silicon heterojunction bipolar-transistors with amorphous and microcrystalline emitters

Abstract The emitter Gummel number of bipolar transistors with an amorphous silicon emitter-base heterojunction is shown to be very large. The temperature dependence of the common-emitter current gain of such heterojunction bipolar transistors is much smaller than that of conventional homojunction transistors. With the actual technology the applicability of amorphous silicon emitters is limited by the emitter series resistance which is too high for VLSI applications. Microcrystalline silicon is a promising emitter material as it combines the high emitter efficiency of amorphous silicon emitters with a much lower resistivity, yielding lower emitter resistances.

Comparison between different schemes for passivation of multicrystalline silicon solar cells by means of hydrogen plasma and front side oxidation

Different schemes for passivation of solar cells fabricated using casted multicrystalline silicon from Eurosolare are investigated. The efficiency of solar cells with front side oxide surface passivation, front side and/or back side hydrogen plasma passivation are compared. It is shown that oxide passivation of the front surface combined with hydrogen passivation from the back side is the optimum passivation scheme. A 16.2% top efficiency is obtained on 4 cm2 cells implementing this passivation scheme and a 16.8% top efficiency is estimated with an optimized ARC combination.

A new n/sup +/pn/sup +/ structure with back side floating junction for high efficiency silicon solar cells

A solar cell structure consisting of an n/sup +/p junction cell with a floating pn/sup +/ junction at the back side is proposed. It is proved that the back surface recombination velocity and the dark current in such a structure are greatly reduced in silicon cells with high-quality bulk material and good emitter surface passivation. Open-circuit voltage in the vicinity of 700 mV and efficiencies around 25% under one-sun illumination conditions are calculated for this structure.<<ETX>>

Twodimensional solar cell simulations by means of circuit modelling

In this work, the authors present a circuit model to perform multidimensional solar cell simulations. This model allows for incorporating effects of lateral current flows in solar cells, keeping the required time and computer resources relatively low. The use and sensitivity of the model are described based on its application towards the design of metallisation patterns for locally passivated back surface structures. As a second application, they present the usage of the model to study the influence of different cell parameters such as surface recombination velocities and cell thickness on its performance.

15.9% efficiency solar cells on electromagnetic cold crucible cast multicrystalline silicon

Hydrogen passivation is found very effective in improving the quality of electromagnetically cased (EMC) multicrystalline silicon from Osaka Titanium Co. (OTC), now Sumitomo Sitix Corp.), due to its small grain size and low oxygen content. A top efficiency of 15.9% is achieved for a 4 cm2 solar cell fabricated on hydrogen passivated EMC‐OTC multicrystalline silicon. Such a result is comparable to the top efficiencies achieved on high quality conventionally casted material and represents the maximum efficiency ever reported for EMC multicrystalline silicon. Fourier transform infrared measurements confirm the low oxygen content in the EMC‐OTC material and spectral response as well as contactless lifetime measurements confirm the role of the plasma hydrogen passivation in substantially improving the diffusion length in this material.

Enhancement of diffusion length of pregettered multicrystalline silicon solar cells by hydrogen ion implantation at the end of the process

2×2 cm2 n+pp+ multicrystalline silicon solar cells have been fabricated using thin wafers less than 200 μm thick. A large electron diffusion length has been achieved in these wafers after metallic impurity gettering using a heavy phosphorus diffusion prior to cell processing. Further improvements in the electron diffusion length (Ln) and in the short circuit current (Jsc) of these cells are brought out by hydrogen ion implantation carried out through the back surface of the finished cell. A 25% increase in Ln and a 5.5% increase in Jsc are obtained.

Optimization of silicon solar cell emitters for maximum cell efficiency

The optimum efficiency of n/sup +/p silicon solar cells is determined, taking into account the different factors affecting the photogenerated current, open-circuit voltage, and fill factor. Saturation currents and photogenerated currents are calculated for cells with a Gaussian emitter doping profile. Geometrical and resistive factors are linked to the electrical data, and an optimum design for the front side contact is obtained. Contours of constant optimum efficiency are given. These contours represent a practical tool for determining the optimum efficiency resulting from a particular technology or designing the best technology for a predetermined value of efficiency.<<ETX>>