Novel, high-throughput metrology methods are used in this paper for detailed performance loss analysis of approximately 400 industrial crystalline silicon solar cells, all coming from the same production line. The characterization sequence combines traditional global cell measurements (e.g., current–voltage, Suns- ${V}_{\text{OC}}$ ) with camera-based cell imaging of voltage distribution and power dissipation from photoluminescence and lock-in thermography, respectively. Spatial variations in current collection are visualized using a high-speed external quantum efficiency and reflectance measurement technique. A nondestructive transfer length method (TLM) measurement technique is also implemented, featuring circular TLM structures hidden within the busbars of the cells. The variance of individual loss parameters and their impact on cell performance are quantified for this large group of cells. Based on correlations performed across parameters, recombination losses in the bulk and rear surface of the cell are shown to be the primary limiting factor for the cell efficiency. The nature of these distributions and correlations provide important insights about loss mechanisms in industrial solar cells, helping to prioritize efforts for optimizing the performance of the production line. Additionally, many of the parameters extracted from these techniques can be tied back to incoming material quality issues (e.g., poor bulk carrier lifetime, nonuniform wafer doping) and to individual unit processes (e.g., texturing, phosphorus diffusion, silicon nitride deposition, metallization), allowing the data to be used directly for process control in manufacturing. All of the datasets are made available for download.

A Comprehensive Methodology to Evaluate Losses and Process Variations in Silicon Solar Cell Manufacturing

Characterization of front contact degradation in monocrystalline and multicrystalline silicon photovoltaic modules following damp heat exposure

Impact of firing temperature on fire-through metal contacts to P-doped (n+) and B-doped (p+) poly-Si

Spatial Atomic Layer Deposition of Molybdenum Oxide for Industrial Solar Cells

Reliable characterization techniques to accurately quantify the metallization-induced recombination losses as well as contact resistivity losses of screen-printed cells are crucial for successful optimization of the contact grid design. Previously, the dark saturation current density at the contact ( ${J}_{\rm 0c}$ ) is often assumed to be constant for different finger width. Similarly, impact of finger width on contact resistivity ( ${\rho }_{\rm c}$ ) is rarely reported. Therefore, we performed a comprehensive evaluation of  ${J}_{\rm 0c}$ and ${\rho }_{\rm c}$ as a function of finger width, spacing as well as firing temperature. We found out that ${J}_{\rm 0c}$ increases from $\approx$ 2000 to $\approx$ 8100 $\text{fA/cm}^{2}$ , when the finger width increases from 60 to 400 $\mu$ m; and ${\rho }_{\rm c}$ decrease from 7.2 to 2.2 $\text{m}{\Omega }\cdot \text{cm}^{2}$ when using a wide -TLM rather than a narrow -TLM structure, for samples fired at 840  $^{\circ }$ C. Based on our cross-sectional and top-down scanning electron microscopy images, we believe that the physical root cause can be explained by the difference in the microstructure formed at the metal–silicon interface during the firing process for the screen-printed contacts.

A Comprehensive Evaluation of Contact Recombination and Contact Resistivity Losses in Industrial Silicon Solar Cells

Several methods have been determined for measuring the contact resistivity of solar cell devices, but these methods are all either destructive in nature or require the fabrication of special metal contacts. In this paper, we present a non-destructive method for measuring the contact resistivity of commercial grade solar cells using the circular transmission line method. We first determine an optimal method for probing the total resistance of these structures on a solar cell and investigate the importance of measuring the exact dimensions of each contact. Then, by comparing the results of the measurement to traditional TLM results, we select a proper geometry for the circular patterns so that they can be hidden within the busbars of finished cells and not affect cell efficiency or aesthetic. Good correlation is demonstrated between automated circular TLM measurements performed on a new tool, the ContactSpot-PRO, and traditional TLM measurements performed manually. The implementation of this high-speed tool can allow contact resistance to be measured on every R&D or production cell with only a minor change in front silver paste screen artwork.

Non-Destructive Contact Resistivity Measurements on Solar Cells Using the Circular Transmission Line Method

The contact resistivity ( $\rho _c$ ) of screen-printed contacts is a significant component of series resistance in industrial solar cells. Measuring  $\rho _c$ with standard techniques, such as the transmission line method (TLM), requires that the custom printed test structures be isolated from the device. In this article, we present a method for measuring  $\rho _c$ on solar cells using the circular TLM (cTLM), where the test structures are hidden within the busbars of the solar cell. This alleviates the need for the test structure to be isolated from the device, allowing for the fast and nondestructive measurement of  $\rho _c$ without causing additional shading on the cell. These measurements are performed with a semiautomatic tool, the ContactSpot-PRO, used for the accurate and systematic measurement of the  $\rho _c$ on the cTLM structures. Our results show that the cTLM technique compares well to the linear TLM technique on several samples fired through a  range of temperatures. However, numerical models generated using  Quokka3 and scanning electron microscopy images indicate that structural differences in screen-printed TLM and cTLM structures affect the actual contact resistivity of each pattern. The numerical models also show how nonuniform sheet resistance beneath and in-between the printed contacts can affect the measured  $\rho _c$ when using both the TLM and cTLM.

Nondestructive Contact Resistivity Measurements on Solar Cells Using the Circular Transmission Line Method

In this work, novel, high-throughput metrology methods are used to perform a detailed performance loss analysis of $\approx$400 industrial crystalline silicon solar cells, all coming from the same production line. The characterization sequence includes a non-destructive transfer length method (TLM) measurement technique featuring circular TLM structures hidden within the busbar region of the cells. It also includes a very fast external quantum efficiency and reflectance measurement technique. More traditional measurements, like illuminated current-voltage, Suns$V _{OC}$, and photoluminescence imaging are also used to carry out the loss analysis. The variance of the individual loss parameters and their impact on cell performance are investigated and quantified for this large group of industrial solar cells. Some important correlations between the measured loss parameters are found. The nature of these distributions and correlations provide important insights about loss mechanisms in a cell and help prioritize efforts to optimize the performance of the production line.

Zhihao Yang

Papers

A Comprehensive Methodology to Evaluate Losses and Process Variations in Silicon Solar Cell Manufacturing

A Comprehensive Evaluation of Contact Recombination and Contact Resistivity Losses in Industrial Silicon Solar Cells

Non-Destructive Contact Resistivity Measurements on Solar Cells Using the Circular Transmission Line Method

Nondestructive Contact Resistivity Measurements on Solar Cells Using the Circular Transmission Line Method

Detailed Performance Loss Analysis of Silicon Solar Cells using High-Throughput Metrology Methods