The Effect of Light Wavelength and Luminescent Down-Shifting on Solar Cell Current Generated

Overview

This project explores how light color and luminescent down-shifting (LDS) can improve monocrystalline solar cell current generation and present strategies to optimize solar energy capture in real world settings. The objective was to find the effect of different light wavelengths and the effect of LDS on solar cell current generated. A band gap is the minimum energy for an electron to jump from the valence to conduction band in a material, leaving a hole (electron absence) in the valence band. This produces an electron-hole pair, generating current. Monocrystalline solar cells are made of the semiconductor silicon, which has a band gap of 1.1 eV. Recombination occurs when an electron recombines with a hole. Shockley-Read-Hall (SRH) and surface recombination occur when there are traps or dangling bonds, respectively, causing energy loss as heat and not added to current. Silicon’s indirect band gap causes a low light absorption coefficient near its band gap. Red light has about 1.8 eV, closer than infrared or orange light. It was hypothesized that white light would generate the most current, and longer visible light wavelengths would generate more current due to their lower absorption coefficient, penetrating deeper into silicon, reducing recombination losses and improving electron-hole pair collection. The current generated by solar cells covered with and without color filters was measured. The red and green groups generated less current than expected, with the orange group generating the most. This was probably because red light’s lower absorption coefficient causes less overall amount of photons to be absorbed, and green light, being in the middle, does not benefit from more absorption or low recombination losses. Based on these findings, a second experiment was conducted to use LDS to convert high-energy photons to lower energy through the Stokes shift, implemented by placing fluorescent highlighter ink mixed with isopropyl alcohol on plastic wrap over the solar cell. The fluorescent dye groups generated less current than the white-light groups under high light intensity probably due to re-emission losses mainly due to the isotropic (in all directions) emission of fluorescent dye, which resulted in some photons not entering the silicon. However, they generated 4.3 times as much current under low intensity, likely because of lower photon flux (fewer photons hitting the surface) and higher efficiency. This indicates that using LDS under low light intensities can improve solar cell performance, as in practical settings like mornings, evenings, and cloudy days.

Competition history

• CSEF 2026 Alternative Energy (Junior Division) · Entry J-01-04

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