Glass Substrate Composition for Solar Cell Thermal Stress Reduction
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Solution Overview
Problem
Conventional soda lime glass substrates for solar cells and other applications suffer from deformation at high temperatures, generating stress due to thermal expansion mismatch with thin films, limiting photoelectric conversion efficiency and requiring a glass substrate with higher heat resistance, lower thermal expansion coefficient, and suitable for continuous float process production.
Innovation Solution
A glass substrate composition with 58.5-69.5% SiO2, 2.5-9.9% Al2O3, 0-2.5% Li2O, 0-6% Na2O, 0-5.2% MgO, 3-13% CaO, 10-27% SrO, 0-5% BaO, 0-3% TiO2, and 0-9.8% ZrO2, having a glass transition point above 555°C and a liquidus temperature of 1200°C or lower, which reduces stress and production costs while maintaining low density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If soda lime glass is used as substrate, then production cost is reduced and ease of manufacture is improved, but heat resistance deteriorates causing substrate deformation at high temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the glass substrate by specifying precise ranges for SiO2 (58.5-69.5%), Al2O3 (2.5-9.9%), Li2O (0-2.5%), Na2O (0-6%), MgO (0-5.2%), CaO (3-13%), SrO (10-27%), BaO (0-5%), TiO2 (0-3%), and ZrO2 (0-9.8%), achieving a strain point of 500°C or higher while maintaining manufacturability
2Reliability
If high temperature treatment is applied to enhance photoelectric conversion efficiency, then semiconductor efficiency is improved, but substrate deformation increases due to thermal expansion mismatch
Solution Approach 1:
The patent adjusts the thermal expansion coefficient parameter of the glass substrate by controlling the composition ratios, specifically achieving an average thermal expansion coefficient of 75×10−7/°C. or less in the temperature range of 50 to 350° C., which matches the thermal expansion characteristics of the thin film and prevents stress generation during high temperature treatment
Solution Approach 2:
The patent creates a composite glass composition combining multiple oxides (SiO2, Al2O3, Li2O, Na2O, MgO, CaO, SrO, BaO, TiO2, ZrO2) in specific proportions to achieve both high strain point and matched thermal expansion coefficient with the thin film layer
3Weight of moving object
If glass substrate density is reduced to lighten weight for large area panels, then handling is improved, but manufacturing complexity increases due to float process constraints
Solution Approach 1:
The patent optimizes the density parameter by controlling the glass composition, particularly limiting BaO to 0-5% and SrO to 10-27%, achieving a density of 2.83 g/cm³ or less while ensuring the glass can still be manufactured by the float process with appropriate liquidus temperature (1200°C or lower) and working temperature characteristics
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed glass substrate allows for higher heat treatment temperatures, reduced thermal stress, enhanced photoelectric conversion efficiency, and cost-effective production with a suitable thermal expansion coefficient and density, making it suitable for large-area solar cells and other displays.
Implementation Method 1
the soda lime glass has a thermal expansion coefficient of about 90×10−7/° C. When, on a glass substrate made of soda lime glass, a thin film having a thermal expansion coefficient largely different from that of this substrate is formed at a high temperature of 500° C. or more, a high remaining stress is generated between the glass substrate and the thin film
Implementation Method 2
the glass substrate has a glass transition point higher than 555° C.
Data Source
AI summary
The glass substrate of the present invention includes, in terms of mass %: 58.5-69.5% SiO2, 2.5-9.9% Al2O3, 0-2.5% Li2O, 0%≦Na2O<6%, 0%≦K2O<6%, 0% <MgO≦5.2%, 3%<CaO≦13%, 10-27% SrO, 0%≦BaO<5%, 0-3% TiO2, and 0-9.8% ZrO2. SiO2+Al2O3≦73%, Li2O+Na2O+K2O<6%, 3%<MgO+CaO≦16%, SrO+BaO 10-27%, MgO+CaO+SrO+BaO 21-33%, and MgO/CaO 0.2-1.0 in molar fraction. The glass substrate is substantially free from B2O3. Glass transition point >555° C., liquidus temperature ≦1200° C., and average thermal expansion coefficient ≦75×10−7/° C. The present invention can provide a glass substrate having a thermal expansion coefficient close to those of a semi conductor film, etc. and a high strain point, and suitable for continuous production by a float process.