Fast Optical Measurement System: Ultrafast external quantum efficiency measurements on silicon solar cells

- An ultrafast external quantum efficiency (EQE) measurement system is described.
- The typical EQE measurement time is reduced by three orders of magnitude.
- The measurement accuracy is verified on different types of silicon solar cells.
- An outlook towards future developments and use of the system is provided.

Measuring the external quantum efficiency (EQE) of a solar cell is a standard method to gain deeper insights into its opto-electrical properties. For the case of crystalline silicon solar cells, the EQE of a solar cell is often used to assess the quality of the emitter and the passivation scheme. However, the standard EQE measurement method employs a monochromator which means that several minutes are typically needed to complete a single measurement. In academic environments this can form a bottleneck in the research output, while in industrial environments with production speeds of at least 1800 wafers/hour EQE measurements cannot be readily used. In this work, we introduce a new patented characterization tool which we call the Fast Optical Measurement System (FOMS). When using the FOMS, it becomes possible to measure the EQE of amorphous and crystalline silicon solar cells about 3 orders of magnitude faster when compared to a conventional monochromatic measurement. This means that a measurement of the full visible/near-infrared (VIS/NIR) spectrum can be done in 1-10 s, without compromising on accuracy. Additionally, the FOMS can also be used to perform ultrafast reflectance/transmittance once further add-ons to the system are implemented. This opens a path to many optical applications, also outside the photovoltaics field, where fast and accurate broadband measurements are needed.