Hydrogenated Amorphous Silicon Oxide Solar Cells Fabricated near the Phase Transition between Amorphous and Microcrystalline Structures

Abstract

We investigated the properties of hydrogenated amorphous silicon oxide (a-Si 1Àx O x :H) deposited near the phase transition between amorphous and microcrystalline structures. a-Si 1Àx O x :H films were prepared by plasma-enhanced chemical vapor deposition using a gas mixture of silane, hydrogen, and carbon dioxide. The film structure was changed from amorphous to microcrystalline phase by increasing hydrogen dilution. Optical and electrical characterizations revealed that wide-gap a-Si 1Àx O x :H films were deposited under phase transition conditions. We also fabricated a-Si 1Àx O x :H single-junction p-i-n solar cells by varying the hydrogen dilution for the i-layer. The solar cells showed a maximum open circuit voltage of 1.04 V (J sc ¼ 7:92 mA/cm 2 , FF ¼ 0:64, E ff ¼ 5:2%) when the i-layer was deposited under phase transition conditions.

Light-induced Voc increase and decrease in high-efficiency amorphous silicon solar cells

“…[2][3][4][5][6][7] Not only do a-Si:H layers suffer from LID, but amorphous silicon alloys such as amorphous silicon carbide (a-SiC:H) and amorphous silicon oxide (a-SiO:H) also degrade. [8][9][10] Both carbon and oxygen are often used to widen the bandgap of intrinsic or doped amorphous silicon-and there is no reason why alloys using them would not degrade when they are boron doped.…”

Advances in Thin-Film Si Solar Cells by Means of SiOx Alloys

“…Rather high flow rate of hydrogen (H 2 ) was also included in the gas mixture in order to reduce the defect density in the material, which increases with oxygen concentration [6]. The H 2 dilution has to be carefully controlled to obtain device-quality a-SiO x :H with a wide bandgap.…”

“…This can be attributed to the bandgap widening that causes a reduction of the photogenerated carrier density. However, since σ L is proportional to the mobility-lifetime product of the generated carriers, its reduction could be also ascribed to an enhanced content of defects acting as recombination sites, caused by the incorporation of oxygen atoms [6].…”

“…The development of wide bandgap Si-based absorber materials is then a crucial factor for exploiting the efficiency potential of multi-junction solar cells. In this context, hydrogenated amorphous silicon oxide (a-SiO x :H) appears to be a promising candidate, since its energy gap can be significantly widened by adjusting the oxygen content [6][7][8]. Silicon oxide alloys can be useful also as more transparent inactive layers, thus helping to reduce the parasitic light absorption.…”

Plasma monitoring and PECVD process control in thin film silicon-based solar cell manufacturing

“…Moreover, the refractive index and the electronic band gap and, thus, the optical absorption of the material can be varied by alloying of the material with carbon and oxygen, e.g. by the admixture of CH 4 or CO 2 to the process gas [9][10][11][12][13]. Due to the a e-mail: onno.gabriel@helmholtz-berlin.de wide spread and large variety of applications of these films the growth mechanism of thin film silicon is the topic of ongoing research.…”