What are QE and IPCE?
Quantum Efficiency, or IPCE (Incident Photon-to-electron Conversion Efficiency), is the conversion ratio of the incident photon to electron by a photovoltaic cell. For instance, if there are 100 photons irradiating on the surface of the solar cell and 80 electrons are generated, the Quantum Efficiency of the cell is 80%. Furthermore, because Quantum Efficiency is typically plotted as a curve related to wavelengths, it can also reflect the characteristics under variouw wavelengths, whichhelp diagnose the process to improve the efficiency of the solar cell.
In the figure above, the yellow line represents the perfect Quantum efficiency of this solar cell in an ideal case. However, the real QE will be affected by various factors. For example, Quantum Efficiency in the short wavelength range will be reduced by the front surface recombination; in the infrared range, it can be decreased by the rear surface passivation and the diffusion length.
Therefore, Quantum Efficiency is a critical indicator to evaluate the performance of the photovoltaic device. While research laboratories need QE to examine the characteristics of their materials, increasing number of solar cell manufacturers implement QE into their quality control standards, substantiating the importance of acquiring a precise Quantum Efficiency measurement system.