Low‐Temperature Surface Passivation of Silicon for Solar Cells

Abstract

Low-temperature-deposited silicon nitride and aluminum oxide films are investigated for reducing carrier recombination at the silicon surface. The insulator/silicon interface properties (fixed charge density, fast interface state density, and surface recombination velocity) are studied as a function of deposition and annealing temperature in the range of 270 ~ 550~ The effects of UV irradiation and their elimination by charge-induced passivation are extensively discussed. The successful application of both films for front surface passivation of a novel thin-silicon solar cell of the back collection type (BACK-MIS cell) is demonstrated. Finally, a simple configuration for efficient back surface passivation of solar cells is introduced as a possible substitute for the conventional back surface field.The achievement of high efficiencies for crystalline silicon solar cells is highly dependent on the reduction of carrier recombination at the surface (1, 2). Two different techniques are presently applied to obtain low effective surface recombination velocities; (i) growth of a thermal oxide film to reduce surface state density, and (ii) creation

Stability of Al2O3 and Al2O3/a-SiNx:H stacks for surface passivation of crystalline silicon

“…We explain the improvement of the Al 2 O 3 surface passivation under UV exposure by a significant increase of the fixed negative charge density, which was already reported in the pioneering work of Hezel et al for pyrolysis-grown Al 2 O 3 . 22 This photon induced charge injection process was recently also observed for Al 2 O 3 films synthesized by ALD during a laser spectroscopic study. 23 A similar beneficial effect from charge injection was also reported for AlF 3 films.…”

“…23 A similar beneficial effect from charge injection was also reported for AlF 3 films. 24 Furthermore, the reported UV stability of the interface defect density 22 From mass spectrometry cracking patterns, the most likely parent molecules contributing to the signals at the selected mass-to-charge ratios have been determined. The transients are offset for clarity.…”

High-efficiency Silicon Heterojunction Solar Cells: A Review

“…Wet-thermal oxides are grown at lower temperatures [10], and have proven their use in solar cells [11,12]. Other PV-suitable dielectrics include amorphous siliconnitride (a-SiN x :H) [13,14], SiO 2 /a-SiN x :H stacks [9,15], or aluminum-oxide (Al 2 O 3 / films [16][17][18]. As the frontside passivation layer is insulating, contacts to the emitter are made by "spiking" the metal (usually silver) to the emitter, making direct contact with the electronically active absorber [19][20][21].…”

Crystalline silicon surface passivation by the negative-charge-dielectric Al<inf>2</inf>O<inf>3</inf>

“…In the late eighties AI203 was already applied for c-Si surface passivation in a metal insulator-semiconductor (MIS) solar cell by Hezel and Jaeger. [1] that AI203 grown by atomic layer deposition (ALD) could provide an excellent level of surface passivation on p-type c-Si. [2] In this contribution we will demonstrate that AI203 deposited by plasma-assisted ALD [3,4] yields a state-of the-art level of surface passivation on various c-Si surfaces.…”