Driven by Both Quantum Efficiency and Spectral Response: Research on the Optical Properties and Power Enhancement of Coated Glass for BC Cell Modules

Photovoltaic glass not only needs to protect and support solar cells but also needs to have high light transmittance to maximize the absorption of light. The spectral response characteristics of solar cells determine their ability to absorb sunlight. Optimizing these characteristics is crucial for improving the overall efficiency of photovoltaic modules. 

The selection of coated glass for photovoltaic modules directly affects the power and weather resistance of the modules. An improvement in light transmittance can effectively reduce the cost-benefit ratio of photovoltaic modules. Research shows that a 1% increase in the light transmittance of photovoltaic glass can significantly reduce the cost-benefit ratio.

Research Methods

Three types of coated glass:

A: Standard low-iron coated glass (light transmittance: 93.98%);

B: Low-iron coated glass with high light transmittance (light transmittance: 94.63%); 

C: Low-iron coated glass with optimized light transmittance in the short wavelength band (400-550 nm).

Compare the effects of coated glasses with different iron contents (A vs B) and band optimization (B vs C) on the electrical performance of BC modules, and test the influence of the difference in reflectivity on the power of the modules (low-iron and low-reflectance glass vs. ordinary low-iron glass). 

The Relationship between Light Transmittance and Power

Performance data of BC modules encapsulated with coated glass of different iron contents

The curve chart of light transmittance of coated glass with different iron contents

The full-band light transmittance of glass B (94.63%) is higher than that of glass A (93.98%), indicating that glass B has better overall light - transmission performance. Both glasses have relatively high light transmittance in the wavelength range of 320 - 1100 nm, but exhibit strong reflectivity for light with wavelengths greater than 1200 nm.

Power comparison: The average power of the modules encapsulated with glass A is 470.10 W, and the average power of the modules encapsulated with glass B is 470.29 W, with a difference of only 0.19 W.

The increase in the full - band light transmittance (glass B) has not significantly increased the power of the modules, indicating that there is no linear relationship between the light transmittance and the power growth.

Analysis of Spectral Response Matching

Spectral Intensity Diagram of BC Cell

The BC Cell has the strongest spectral response in the wavelength band of 400-550 nm, and this band contributes the most to the power of the module. Therefore, optimizing the light transmittance of the photovoltaic glass in this wavelength band to match it with the spectral response curve of the BC Cell is the key to improving the power of the module.

Quantum Efficiency Diagram of BC cell

The quantum efficiency of BC Cells varies significantly at different wavelengths. The wavelength bands with high quantum efficiency indicate that the batteries can more effectively convert photon energy into electrical energy at these wavelengths.

Short-wavelength region (ultraviolet and blue light, wavelength < 500 nm): The quantum efficiency is relatively high, indicating that the BC battery has good absorption and conversion efficiency for short - wavelength light (such as 400 - 500 nm). This is because photons of short - wavelength light have higher energy, which makes it easier to excite electron transitions.

Long-wavelength region (infrared light, wavelength > 700 nm): The quantum efficiency gradually decreases, indicating that the BC battery has a relatively low absorption and conversion efficiency for long-wavelength light. This is because the photons of long-wavelength light have lower energy, which is insufficient to effectively excite electron transitions.

Experiment of Encapsulation with Coated Glass with High Transmittance in the Short Wavelength Band.

The Curve Chart of Light Transmittance of B and C Low-Iron Coated Glass

Electrical performance data of BC modules encapsulated with coated glass of the same iron content

The light-transmittance curves of two types of low-iron coated glasses, B and C, are presented. The light transmittance of glass C in the 400-550 nm wavelength band is significantly higher than that of glass B (especially reaching a peak near 450 nm).

The electrical performances of BC modules encapsulated with glass B and glass C were compared. The average power of the modules with glass C is 472.97 W, which is 2.677 W higher than that of the modules with glass B, and the short-circuit current (ISC) is increased by 0.063 A. By increasing the light transmittance in this wavelength band, glass C enables more high-energy photons to be effectively utilized, thus significantly improving the short - circuit current and the maximum power.

Experiment of Encapsulation with Low-Reflection Coated Glass in the Short Wavelength Band

Diagram of the Interrelationships among Spectral Irradiance Density, Wavelength and Photon Energy

The curve shows that the irradiance density of sunlight reaches its peak at around 500 nm. This indicates that in the visible light region (especially in the green light region), the number of photons of sunlight is the largest and the energy is the most concentrated.

In the short-wavelength region (such as ultraviolet light with a wavelength < 400 nm), the spectral irradiance density is relatively low, but the photon energy is high (photon energy is inversely proportional to the wavelength).

In the long-wavelength region (such as infrared light with a wavelength greater than 700 nm), the spectral irradiance density gradually decreases, and the photon energy is also relatively low.

The Reflectivity Curve Chart of Two Kinds of Colorless Coated Glasses

Electrical performance data of BC modules encapsulated with low-iron colorless coated glasses of different reflectivities

Reflectivity and Light Loss: The reflectivity of low-iron low-reflection glass in the visible light range (below 500 nm) is significantly lower than that of ordinary low - iron glass. This reduces light loss and increases the intensity of incident light.

Light Energy Input and Short-Circuit Current: The reduction in reflectivity directly increases the number of photogenerated carriers, resulting in an increase of 0.09 A in the short - circuit current (ISC), which in turn enhances the power of the module.

Reducing the reflectivity of coated glass is an effective strategy to enhance the power of the modules. The reflectivity of low-iron low-reflection glass in the visible light range is significantly lower than that of ordinary low-iron glass, which reduces light loss and increases the photogenerated current, thereby significantly improving the short-circuit current and the maximum power.

Although its light transmittance is slightly lower, the low reflectivity leads to higher light energy utilization efficiency in the short wavelength band, matching the spectral response and quantum efficiency of BC cells.

Through an in-depth study of the optical properties of low-iron coated glass and the performance of BC cell modules, the crucial role of optimizing reflectivity and transmittance in improving the efficiency of photovoltaic modules has been revealed. The experimental results show that, relying on its low reflectivity characteristics in the short-wavelength region (such as 400-500 nm), the low-iron, low-reflection, colorless coated glass significantly reduces the reflection loss of light and highly matches the high spectral response region of BC cells, thus achieving a remarkable increase in the power of the modules.

MNPVQE-300 Quantum Efficiency Measurement System

Email：market@millennialsolar.com

The MNPVQE-300 QE Quantum Efficiency Measurement System can be used to measure the spectral response of solar cells and diagnose the problem of low spectral response areas in solar cells through their quantum efficiency. It has the advantages of universal compatibility, a wide spectral measurement range, test accuracy, and traceability.

✔  Compatible with all types of solar cells, meeting various testing requirements.

✔  The spectral range can reach 300-2500 nm, and special customization is provided. n

✔  The dual light source structure of xenon lamp and halogen lamp ensures the stability of the light source.

Future research can further explore the spectral matching between other types of solar cells and different coated glasses, and develop more efficient and economical photovoltaic modules. At the same time, by combining advanced testing equipment, such as the MNPVQE-300 QE Quantum Efficiency Measurement System,it is possible to more comprehensively evaluate the performance of photovoltaic modules and contribute to the achievement of sustainable energy goals.