Elimination of LID with innovative new hydrogenation technology facilitates increased PERC cell efficiencies through the use of lower resistivity p-type Cz wafers

Tan, Matthew, Wenham, Stuart, and Chong, Chee Mun (2016) Elimination of LID with innovative new hydrogenation technology facilitates increased PERC cell efficiencies through the use of lower resistivity p-type Cz wafers. In: Extended Abstracts from the Photovoltaic Science and Engineering Conference. From: PVSEC-26: 26th Photovoltaic Science and Engineering Conference, 24-28 October 2016, Singapore.

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Silicon photovoltaics has always dominated commercial manufacturing, with p-type Cz and multi being the wafers of choice. However the light-induced degradation (LID) due to B-O defects has been a major problem for industrial p-type Cz wafers for decades. This has necessitated the use of more lightly doped wafers than would normally be considered optimal so as to reduce the B concentration and hence the B-O defect formation. This is particularly the case with PERC cells where the lower wafer doping concentration leads to increased lateral resistive losses and higher resistive losses in the vicinity of the rear point contacts. In this work, CEC Energy and UNSW Australia have been working together to exploit the use of atomic hydrogen to passivate defects, particularly B-O defects, within p-type Cz silicon solar cells. Innovative new technology has been developed to control the charge state of interstitial atomic hydrogen atoms within the silicon lattice, which in turn has facilitated improvements in both the diffusivity and reactivity of the hydrogen atoms.

Use of this innovative hydrogenation technology has demonstrated that by controlling the charge-state, hydrogen atoms can be used to passivate B-O defects and other recombination mechanisms within the silicon wafers, transforming the quality and stability of commercial grade p-type Cz silicon wafers, into the equivalent of the very best wafers used by the semiconductor industry that can cost as much as one hundred times more. This potentially enables the use of significantly lower cost wafers in PV manufacturing without performance loss and in fact has simultaneously demonstrated marked improvements in both efficiency and stability.

CEC Energy and UNSW in Australia have developed a prototype production hydrogenation tool that is suitable for demonstrating the hydrogenation technology on large area production solar cells. In particular, this prototype production tool enables the implementation of the hydrogenation technology to solve light-induced degradation in commercial-grade p-type Czochralski (Cz) wafers as well as appearing to also passivate many other forms of recombination potentially due to contamination and crystallographic imperfections.

This new prototype production tool was specifically used to investigate the impact of the innovative hydrogenation technology on the performance and stability of CEC silicon solar cells that are fabricated from low resistivity (0.5 ohm-cm) p-type Cz on normal PERC solar cell production lines. These solar cells after treatment were stable and no longer susceptible to light-induced degradation following the hydrogenation treatment.

In this work, PERC silicon solar cells using industrial grade 0.5 ohm-cm p-type Cz wafers were fabricated on an existing standard PERC cell production line to the specifications of CEC Energy. These cells are 156-cm x 156-cm screen printed PERC silicon solar cells. Being fabricated from low resistivity commercial-grade p-type Cz silicon wafers, these CEC solar cells are subject to higher than normal levels of light induced degradation, with losses approaching 10% through only 48 hours of light-soaking at 78 mW/cm2 and 40degC.

A total of 8 CEC solar cells were divided into two groups of 4 cells each (Group 1 and Group 2). The solar cells from these two groups were put through the following process: 1) Obtain PL images and IV characteristics of all the CEC solar cells; 2) Solar cells from Group 1 were set aside (no treatment) while the solar cells from Group 2 were treated in the prototype hydrogenation tool using appropriate illumination ramping, peak illumination of 20-suns, peak temperature of 280degC and rapid cooling; 3) Obtain PL images and IV characteristics of the Group 2 solar cells after hydrogenation treatment; 4) All the cells were subjected to a prolonged light soaking step performed at 40 deg C and 78 mW/cm2 under halogen lamp illumination for 48 hours; 5) Obtain PL images and IV characteristics of the cells following the prolonged light soaking step.

Item ID: 51424
Item Type: Conference Item (Presentation)
Keywords: hydrogenation technology, overcoming LID, use of renewal energy for aquaculture
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Date Deposited: 06 Nov 2017 23:31
FoR Codes: 09 ENGINEERING > 0906 Electrical and Electronic Engineering > 090605 Photodetectors, Optical Sensors and Solar Cells @ 100%
SEO Codes: 85 ENERGY > 8505 Renewable Energy > 850504 Solar-Photovoltaic Energy @ 100%
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