Intrinsic Amorphous Silicon Bilayers for Effective Surface Passivation in Silicon Heterojunction Solar Cells: A Comparative Study of Interfacial Layers

Abstract

The impact of intrinsic amorphous silicon bilayers in amorphous silicon/crystalline silicon (a‐Si:H/c‐Si) heterojunction solar cells is investigated. Intrinsic a‐Si:H films with a wide range of film densities and hydrogen contents are prepared via a plasma‐enhanced chemical vapor deposition (PECVD) technique by modifying various process parameters. For silicon heterojunction (SHJ) solar cells with a‐Si:H films applied as single i‐layers, the resulting surface passivation at the a‐Si:H/c‐Si interface is poor. However, surface passivation is significantly improved by applying intrinsic bilayers, which are composed of a porous interfacial layer (≈2 nm) and an overlying dense layer (≈8 nm). The microstructure factor R* of the interfacial a‐Si:H layer, which is related to the SiH bond microstructure and determined by infrared absorption spectroscopy, closely correlates to the surface passivation capability of the bilayers. A variety of PECVD process parameters (temperature, pressure, or precursor gas species) can be utilized to grow an interfacial layer for good surface passivation, provided that its R* is controlled within a suitable range. This indicates that R* is a key universal parameter for optimizing i‐bilayers and realizing high‐efficiency SHJ solar cells.

Very thin crystalline silicon cells: A way to improve the photovoltaic performance at elevated temperatures

“…The detail condition of our PECVD process was reported elsewhere. 19,28,29 In this study, we prepared two different groups of SHJ solar cells by controlling the deposition condition of (i)a-Si:H in terms of surface passivation, that is, the samples with our standard deposition condition (Group A) and those with intentionally deteriorated surface passivation and therefore lower conversion efficiencies (Group B). After the PECVD process, In 2 O 3 :Sn (ITO) films and Ag electrodes were formed on both sides of the precursor by means of magnetron sputtering with shadow masks.…”

Very Thin (56 μm) Silicon Heterojunction Solar Cells with an Efficiency of 23.3% and an Open‐Circuit Voltage of 754 mV

“…Two‐step growth of (i)a‐Si:H was applied at both the front and the rear surfaces for better surface passivation. [ 71,72 ] The detailed growth conditions for the (p)a‐Si:H and (p)nc‐Si:H layers are shown in Table 1 . Prior to the growth of (p)nc‐Si:H layers, a CO 2 plasma treatment was applied to the (i)a‐Si:H surface for 30 s to promote an immediate crystalline nucleation at the interface.…”

“…Two-step growth of (i)a-Si:H was applied at both the front and the rear surfaces for better surface passivation. [71,72] The detailed growth conditions for the (p)a-Si:H and (p)nc-Si:H layers are shown in Table 1.…”

Toward Efficiency Limits of Crystalline Silicon Solar Cells: Recent Progress in High‐Efficiency Silicon Heterojunction Solar Cells

“…[119] A dual-intrinsic layer or bilayer approach is known to be effective to attain good surface passivation at the a-Si:H/c-Si interface. [120][121][122] Zhang et al in 2017 and Ruan et al in 2019 proposed the two-step method to obtain an epitaxial-free passivation bilayer (as shown in Figure 8). [13,123,124] Morales-Vilches et al used a low hydrogen dilution plasma (H 2 :SiH 4 = 1:1) to deposit the buffer layer at the initial state.…”

“…Very recently, Sai et al studied various intrinsic bilayer deposition conditions, with a particular focus on the correlation between the growth condition and the material properties of the interfacial a-Si:H layer. [122,126] For a bilayer approach, the entire deposition process can be divided into the initial deposition stage and the growth stage. Yet, the success of the initial deposition state is critical to obtaining a sharp interface.…”