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

Abstract

S everal 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.

A Novel TLM Analysis for Solar Cells

“…Mathematical analysis: We generate artificial R c , R sh , D f , and W f values, representing a planar TLM structure to create a dummy TLM dataset. Using such a dataset, R tot values between all the terminals of a TLM network are reverse calculated, as shown in ( 9) and (10). Linear fitting and matrix based extraction is carried out on this dataset, and the results are compared.…”

“…2, two such combinations are demonstrated in red and green color for the measurements between Contact 1 to Contact 2 and Contact 1 to Contact 6, respectively. The two measurements can be mathematically represented as (9) and (10) as where R tot x−y represents the total resistance measured between any two contacts x and y. Similarly, R emt x−y is the total emitter resistance in Ω and can be expressed in units of Ω/ by using R sh = R emt (Z f /D f ).…”

“…Various experimental modifications and test structure geometries have also been suggested to improve the accuracy and sensitivity of the TLM [9]- [11]. Guo et al [6] have discussed the potential sources of the errors associated with TLM sample preparation, and Gregory et al [10] have presented a nondestructive technique based on the circular TLM for solar cells to rectify such errors.…”

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

“…The non-destructive cTLM measurements were performed using a BrightSpot Automation ContactSpot-PRO system. The contact resistivity (ρC) and emitter sheet resistance (Rsheet) were extracted from the cTLM measurements using the technique in [6]. The ρC and Rsheet of c-Si solar cells is traditionally measured using TLM measurements, wherein the test structures are created by isolating strips of a cell (e.g., laser scribe then cleave) or by fabricating special test structures within a wafer.…”

“…In this work, we've carried out five different measurement techniques on ≈400 industrial crystalline silicon (c-Si) solar cells, all from the same production line, and will present a detailed performance loss analysis on this statistically relevant group of cells. The five measurement techniques include: (1) illuminated I-V at standard test conditions, a common method used to test and bin cells following their fabrication [2]; (2) Suns-VOC [3]; (3) photoluminescence (PL) imaging [4]; (4) high-speed quantum efficiency and reflectance spectroscopy [5]; and (5) non-destructive transfer length method (TLM) measurements [6].…”