Dimitre Z. Dimitrov

GaGeSb alloys for high-speed reversible phase-change optical recording

New Ga doped GeSb based phase-change materials are investigated. These materials possess good optical contrast at short wavelengths. Crystallization temperature increasing and grain size refinement are obtained by addition of Ga. More than 50 dB CNR and 25 dB erasability are measured in disks with simple four layer stacks using blue laser and linear velocities 7 m/s and 10.5 m/s.

Inverted pyramid texturisation without photolithography for multicrystalline solar cell

New surface texturing method including formation of inverted pyramids has been further investigated in this study. Electroless deposition of Ag particles as metal catalyst in HF/H2O2 etching solution is found to be efficient for drilling nano-size holes into c-Si or m-Si. After etching back by KOH solution, the inverted pyramids structure gradually appears in c-Si (100) surface. Although the m-Si wafers have different orientation grains, the average reflection after texturing demonstrates lower than that of traditional acid treatment. The new texturing wafers were processed into cells with a conventional process including POCl3 diffusion (leading to 65 Ω/□), removal of native oxide by BOE solution. The deviations of sheet resistance on 5″ wafers are controlled below 5% which are consistent with that of acidic or alkaline treatment wafers. The SiNx antireflection coating was deposited uniformly by PECVD deposition. From the results of IV measurement, the conversion efficiency of new texturing has 0.1% higher than that of acidic treatment (texturied by Rena facilities). We expect the optimization of texturisation will lead to more short-circuit current density( Jsc) and gain more conversion efficiencies.

Unified texturization method for mono- and multi-crystalline silicon solar cells

A texturization method suitable for both c- and mc-Si is developed. The method is applied on as-cut wafers and is found to be suitable for combined saw damage removal and texture formation. The texturization with inverted surface structures was obtained using wet chemistry process sequence at room temperatures without using a mask and lithography. Potential for an improvement of the standard screen — printing cells performance by incorporation of the new developed texturization method is demonstrated.

Immersion of silicon solar cells in an oxidation solution

The conventional wafer-type crystalline silicon solar cells have an approximately 80nm thick top SiNx coating which acts as an anti-reflection layer. The SiNx layer also passivates the silicon substrate surface to reduce free electron consumption very near the surface. Besides, it was known that the properties of the SiNx layer itself may, to some extent, affect the performance of the solar cell. The purpose of this study is to provide a low-temperature method that will help to modify the properties of the SiNx film, especially for low-temperature grown SiNx thin layer. This is achieved by immersing the finished silicon solar cells into an oxidation solution containing strong oxidant. Oxidation solution helps to oxidize the low-temperature grown SiNx as well as the weakly passivated silicon surface. By applying the techniques, the properties of the SiNx layer have been modified and an enhancement on cell performance was demonstrated. The results presented in this study show that the properties of the SiNx layer need to be taken with care, because they may affect the performance of the solar cells.