The silane depletion fraction as an indicator for the amorphous/crystalline silicon interface passivation quality

Abstract

In silicon heterojunction solar cells, thin amorphous silicon layers passivate the crystalline silicon wafer surfaces. By using in situ diagnostics during plasma-enhanced chemical vapor deposition ͑PECVD͒, the authors report how the passivation quality of such layers directly relate to the plasma conditions. Good interface passivation is obtained from highly depleted silane plasmas. Based upon this finding, layers deposited in a large-area very high frequency ͑40.68 MHz͒ PECVD reactor were optimized for heterojunction solar cells, yielding aperture efficiencies up to 20.3% on 4 cm 2 cells.

Surface passivation of c-Si for silicon heterojunction solar cells using high-pressure hydrogen diluted plasmas

“…Typically passivating a-Si:H layers are deposited using radio-frequency plasmaenhanced chemical vapour deposition (rf PECVD). 8,9 The pre-deposition processes, i.e. texturing and cleaning, can affect defect creation in the c-Si sub-surface region.…”

Improved amorphous/crystalline silicon interface passivation by hydrogen plasma treatment

“…In this study, we used highly depleted silane plasmas. 4 To come closer to this transition without risking epitaxial growth, we tested hydrogen (H 2 ) plasma treatments during a-Si:H growth via brief interruptions of deposition. It is known that such treatments can lead to complete crystallization of a-Si:H, due to removal of strained bonds from the a-Si:H growth surface by H atoms.…”

“…Details about the structure and fabrication process of complete heterojunction solar cells are described elsewhere. 4 To investigate the effect of H 2 treatment on the passivating intrinsic layers, two deposition sequences were tested, as shown in Figure 1. The first consisted of a single step of pure silane plasma; the second consisted of three shorter silane plasma steps (same conditions as for the first deposition type) with an additional short H 2 plasma step after each silane step.…”

High quality crystalline silicon surface passivation by combined intrinsic and n-type hydrogenated amorphous silicon

“…This way, the open circuit voltage (V OC ) of these structures can be increased to values exceeding 700 mV. 2,3 Sanyo 1 has introduced this concept in 1992 and, due to its excellent results, inspired many other groups worldwide to focus on this concept.…”

“…Silicon heterojunction (SHJ) solar cells, consisting of hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si), form a potentially inexpensive alternative to standard p-n homojunction c-Si solar cells. [1][2][3][4] In homojunction c-Si cells, the p-n junction is formed by the thermal diffusion of dopants, for which temperatures around 900 C are required. In case of a-Si:H/c-Si based heterojunction solar cell processing, temperatures below 200 C are used, as the p-n junction is formed by depositing a thin doped a-Si:H layer on a c-Si wafer.…”