J. A. Anna Selvan

On the Way Towards High Efficiency Thin Film Silicon Solar Cells by the “Micromorph” Concept

Note: IMT-NE Number: 222 Reference PV-LAB-CONF-1996-008 Record created on 2009-02-10, modified on 2017-05-10

Device grade microcrystalline silicon owing to reduced oxygen contamination

As‐deposited undoped microcrystalline silicon (μc‐Si:H) has in general a pronounced n‐type behavior. Such a material is therefore often not appropriate for use in devices, such as p‐i‐n diodes, as an active, absorbing i layer or as channel material for thin‐film transistors. In recent work, on p‐i‐n solar cells, this disturbing n‐type character had been successfully compensated by the ‘‘microdoping’’ technique. In the present letter, it is shown that this n‐type behavior is mainly linked to oxygen impurities; therefore, one can replace the technologically delicate microdoping technique by a purification method, that is much easier to handle. This results in a reduction of oxygen impurities by two orders of magnitude; it has, furthermore a pronounced impact on the electrical properties of μc‐Si:H films and on device performance, as well. Additionally, these results prove that the unwanted donor‐like states within μc‐Si:H are mainly due to extrinsic impurities and not to structural native defects.

Towards high-efficiency thin-film silicon solar cells with the “micromorph” concept

Tandem solar cells with a microcrystalline silicon bottom cell (1 eV gap) and an amorphous-silicon top cell (1.7 eV gap) have recently been introduced by the authors; they were designated as “micromorph” tandem cells. As of now, stabilised efficiencies of 11.2% have been achieved for micromorph tandem cells, whereas a 10.7% cell is confirmed by ISE Freiburg. Micromorph cells show a rather low relative temperature coefficient of 0.27%/K. Applying the grain-boundary trapping model so far developed for CVD polysilicon to hydrogenated microcrystalline silicon deposited by VHF plasma, an upper limit for the average defect density of around 2 × 1016/cm3 could be deduced; this fact suggests a rather effective hydrogen passivation of the grain-boundaries. First TEM investigations on μc-Si : H p-i-n cells support earlier findings of a pronounced columnar grain structure. Using Ar dilution, deposition rates of up to 9 A/s for microcrystalline silicon could be achieved.

The growth of surface textured aluminum doped ZnO films for a-Si solar cells by RF magnetron sputtering at low temperature

Note: IMT-NE Number: 219 Reference PV-LAB-CONF-1996-012 Record created on 2009-02-10, modified on 2017-05-10

The “Micromorph” cell: a new way to high-efficiency-low-temperature crystalline silicon thin-film cell manufacturing?

Hydrogenated microcrystalline Silicon (μc-Si:H) produced by the VHF-GD (Very High Frequency Glow Discharge) process can be considered to be a new base material for thin-film crystalline silicon solar cells. The most striking feature of such cells, in contrast to conventional amorphous silicon technology, is their stability under light-soaking. With respect to crystalline silicon technology, their most striking advantage is their low process temperature (220 °C). The so called “micromorph” cell contains such a μc-Si:H based cell as bottom cell, whereas the top-cell consists of amorphous silicon. A stable efficiency of 10.7% (confirmed by ISE Freiburg) is reported in this paper. At present, all solar cell concepts based on thin-film crystalline silicon have a common problem to overcome: namely, too long manufacturing times. In order to help in solving this problem for the particular case of plasma-deposited μc-Si:H, results on combined argon/hydrogen dilution of the feedgas (silane) are presented. It is sho...

The “Micromorph” Cell: a New Way to High-Efficiency-Low-Temperature Crystalline Silicon Thin-Film Cell Manufacturing?

Note: IMT-NE Number: 235 Reference PV-LAB-CONF-1997-006 Record created on 2009-02-10, modified on 2017-05-10

The Fiber Texture Growth and the Surface Roughness of ZnO Thin Films

Note: IMT-NE Number: 244 Reference PV-LAB-CONF-1997-018 Record created on 2009-02-10, modified on 2017-05-10