Quantitative evaluation method for electroluminescence images of a‐Si:H thin‐film solar modules

Abstract

This work presents a method for extracting the absolute local junction voltage of a‐Si:H thin‐film solar cells and modules from electroluminescence (EL) images. It is shown that the electroluminescent emission of a‐Si:H devices follows a diode law with a radiative ideality factor nr larger than one. We introduce an evaluation method that allows us to determine the absolute local junction voltage in cases of nr > 1, while existing approaches rely on the assumption of nr = 1. Furthermore, we find that the experimentally determined values of nr vary from sample to sample. It is also explained why the derived radiative ideality factor is influenced by the spectral sensitivity of the camera system used in the experiment. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Efficiency Potential of Photovoltaic Materials and Devices Unveiled by Detailed-Balance Analysis

“…This is the case for the a-Si∶H cell in the present work where radiative recombination rates change nonlinearly with increasing voltage bias [54]. However, the concept of a radiative ideality factor n rad [54,65] provides the possibility to calculate V SQ OC in spite of this complication, as shown in Appendix B. Figure 4 summarizes the open-circuit voltage losses ΔV rad OC , ΔV SC OC , and ΔV nonrad OC for different solar cells.…”

“…In the case of nonideal luminescent emission, we may still describe the dependence of the EL intensity Φ EL on internal voltage with Φ EL ∝ expðqV=n rad kTÞ. The radiative limit V rad OC can then be consistently described using the radiative ideality factor n rad [65,68]…”

Quantitative Analysis of Trap-State-Mediated Exciton Transport in Perovskite-Shelled PbS Quantum Dot Thin Films Using Photocarrier Diffusion-Wave Nondestructive Evaluation and Imaging

“…Moreover, PL is unable to detect the optoelectronic kinetics of the surface and near-surface (junction) regions, which, however, are of key interest for solar cell efficiency enhancement . Electroluminescence imaging of solar cells uses a camera that converts electric fields applied to the device to infrared radiative emission; however, this technique can only be applied to finished and operating solar cells and, thus, is not suitable for substrates and partly processed devices . Homodyne and heterodyne carrierographies introduced by Mandelis et al , as spectrally gated forms of dynamic PL are all-optical and contactless imaging techniques, which can monitor the kinetics of charge carrier transport in junction regions.…”

The Principle of Detailed Balance and the Opto‐Electronic Properties of Solar Cells

“…For every material and for every temperature the luminescent emission may originate from different transitions between free and/or trapped carriers. In this case, all quantitative models based on the determination of the relative voltage from the luminescence emission would become more complicated because the radiative ideality factor n id,rad would have to be determined first by a separate measurement [88]. Instead, the voltage dependence of the radiative recombination current will depend on the density of trapped states and the exact way depends on how probable the different transitions are with respect to each other [86].…”