J. Nijs

Efficiency improvement by porous silicon coating of multicrystalline solar cells

Abstract Shallow junction multicrystalline Si solar cells have been processed by an anodical etching technique. More than 25% improvement in short-circuit current and photovoltaic energy conversion efficiency was demonstrated. It was shown that improved performance was caused by antireflection action of the porous silicon layer as well as by the cell surface and grain boundary passivation.

High-efficiency low-cost integral screen-printing multicrystalline silicon solar cells

This paper describes how the efficiency and throughput of industrial screen-printed multi-Si solar cells can be increased far beyond the state-of-the-art production cells. Implementation of novel processes of isotropic texturing, shallow emitter or single diffusion selective emitter, combined with screen-printed metallization fired through a PECVD SiNx ARC layer, have been described. Novel dedicated fabrication equipment for emitter diffusion and a PECVD SiNx deposition system are developed and implemented thereby removing the processing bottlenecks linked to the diffusion and bulk passivation processes. Several types of back-contacted solar cells with improved visual appeal required for building integrated photovoltaic (BIPV) application have been developed.

Very low temperature (250 °C) epitaxial growth of silicon by glow discharge of silane

Epitaxial growth of phosphorus‐doped silicon deposited at 250u2009°C from a radio‐frequency glow discharge from SiH4 is demonstrated by high‐resolution electron microscopy (HREM) and spreading resistance profile measurements. Thin epitaxial films are present at the interface between (100)u2009Si substrates and hydrogenated amorphous silicon. After recrystallization at 700u2009°C, single‐crystal layers are obtained, in which HREM reveals extensive twinning. The fact that epitaxial growth can take place at 250u2009°C in a system with a background pressure of only 5×10−6 mbar can be attributed to the presence of species in the SiH4 plasma that reduce the native oxide and the use of HF in the cleaning procedure.

Isotropic texturing of multicrystalline silicon wafers with acidic texturing solutions [solar cell manufacture]

The limitations associated with the most widely used anisotropic etching techniques in industrial multicrystalline solar cell manufacturing processes can be reduced by using acidic etching solutions. Optimised etching conditions were found which lower the reflectance from multi-c wafers below levels obtained by anisotropic texturing with NaOH solutions. The surfaces of acidic textured wafers show a very homogeneous distribution of the reflected light. Solar cells produced on acidic textured wafers show higher performance than in the case of alkaline texturing.

Energy of arrays of nonperiodic interacting dislocations in semiconductor strained epilayers - implications for strain relaxation

The interaction energy EirrI of arrays of dislocations with nonperiodic (or irregular) distribution is calculated. The calculations have been made for uniform‐random and Gaussian distributions of dislocations. The method used is, however, general and can also be applied to any arbitrary or an observed distribution of dislocations. The results for several values of average spacing p and standard deviation σ are given and are compared with the energy EI of periodic arrays with spacing p=p. The total energy EirrT of strained layers containing nonperiodic dislocation arrays is also calculated. The results for both 90° and 60° dislocations are given. For sufficiently large numbers of dislocations, EirrI is always larger than EI. The difference between the energies EirrI and EI increases rapidly as the standard deviation σ of the nonperiodic distribution increases. The equilibrium strain relaxation in thick layers and the strain relaxation on annealing the metastable layers are usually calculated by modeling ...

A simple processing sequence for selective emitters [Si solar cells]

A novel method to form selective emitters in only one diffusion step without etching or masking steps has been recently introduced for Si solar cells. A phosphorous containing doping source is applied selectively to the front side of a p-type crystalline Si substrate in the form of a paste and subsequently dried. The print is performed with advanced screen printing equipment that allows very precise positioning. In only one diffusion step, deeply diffused regions form under the printed doping source. At the same time, the adjacent regions become weaker doped by P atoms diffusing indirectly from the printed source through the gas ambient into those regions that were not covered by the P paste. The advantages of such a processing sequence over typical industrial processes are addressed. Results from an ongoing optimisation of such a sequence are given and interpreted.

Electrical and optical bandgaps of Ge/sub x/ Si/sub 1-x/ strained layers

Theoretical and experimental evidence is presented to show that the effective mass of holes is reduced due to strain in the Ge/sub x/Si/sub 1-x/ layers grown on Si

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.

Boosting the efficiency of solar cells fabricated on electromagnetic cold crucible cast multicrystalline silicon by means of hydrogen passivation

Abstract In this work the improvement of the quality of the electromagnetic cold crucible cast multicrystalline silicon (EMC) material produced by Sumitomo Sitix Co. (SCC, previously Osaka Titanium Co.) by hydrogen plasma is investigated with the final goal of realizing solar cells with the maximum posible efficiency. Two different hydrogen passivation techniques are implemented: hydrogen passivation by means of rf (radio frequency) plasma treatment and hydrogen passivation using microwave induced remote plasma treatment. By combining the oxide surface passivation and hydrogen passivation by remote plasma from the front side and by rf plasma from the back side, a significant improvement in short-circuit current, in open-circuit voltage, and in fill factor is obtained. A maximum efficiency of 16% on 2 × 2 cm 2 cells and of 14.5% on 10 × 10 cm 2 cells is achieved. This 16% efficiency is the highest ever reported on EMC multicrystalline silicon.

The DC current—Voltage characteristics of diodes under high-injection conditions

The (J-V) characteristics of n+-p-p+diodes operating under high injection are calculated using a simplified analysis which is in very good agreement with an exact numerical calculation. The analysis is restricted to the case of negligible recombination in the lowly doped base. It is demonstrated that at high injection the commonly used approximationJ = J_{s} exp (V/2V_{t})is not valid if the current results from both electron and hole flow.