Quantitative Determination of Luminescent Coupling in Multijunction Solar Cells from Spectral Photovoltage Measurements

Abstract

7We present a simple method to quantify the magnitude of luminescent coupling (LC) between stacked 8 subcells in multijunction photovoltaic devices. The effect of luminescence produced at high-band-gap 9 subcells on underlying low-gap units within the same device can be directly accessed as a measurable open-10 circuit voltage difference by comparing two photovoltage spectra. Additionally, our study unambiguously 11 identifies LC as the modulation mechanism across multijunction solar cells generating a response from 12 buried subcells in photoreflectance measurements.

Multiscale in modelling and validation for solar photovoltaics

“…Current research efforts concentrate on functionalized layers in addition to standard antireflection coatings to optimize light trapping and exploit local field enhancement of metal nanoparticles via plasmon modes. Plasmon-assisted processes such as direct increase of the charge carrier generation or indirect enhancement of energy conversion effects from neighboring nanocrystal structures have received much interest [139][140][141][142][143][144][145].…”

Combined photo- and electroreflectance of multijunction solar cells enabled by subcell electric coupling

“…7 The application of PR to monolithically integrated optoelectronic devices, like multijunction solar cells (MJSCs), has been demonstrated before. 8,9 The main difficulty in the characterization of such two-terminal devices is the independent optoelectronic diagnosis of each of the series-connected subcells forming the device. The development of spectroscopic techniques capable of complementing the conventionally used ones, like quantum efficiency (QE) or photoluminescence (PL), is therefore of great interest.…”

“…In previous studies, luminescent coupling (LC) between subelements in a monolithic device was identified as an effective mechanism for transmitting the modulating perturbation to otherwise inaccessible parts of the sample. 8 Here, we propose yet a different method for the transmission of the modulation based on the electric coupling between subelements, thus not restricted by the internal quantum yield of the radiative recombination process in the pump beam-absorbing material.…”

“…Previous PR experiments on identical samples with a 325 nm (3.8 eV) pump beam had revealed signatures from both the GaInP-TC and the GaAs-BC. 8 The nature of the modulation mechanism of the BC and the appearance of related signatures in the PR spectra are not straightforward. Considering layer thicknesses and absorption coefficients, full absorption of the 325 nm pump beam is expected at the TC (870 nm, a GaInP ¼ 7.9 Â 10 5 cm À1 ) and its AlInP-window layer (25 nm, a AlInP ¼ 6.7 Â 10 5 cm À1 ) under normal incidence, according to numerical calculations.…”

“…We have previously identified luminescent coupling (LC) 11 as the modulation mechanism responsible for PR-signatures of low gap subcells under TC-excitation and proposed a method to quantify the LC-impact in the form of a measurable photovoltage. 8 Under LC, radiative recombination events occurring at the TC, following photoexcitation with the pump light, generate subsidiary photons that can be re-absorbed at the BC, thereby generating additional photocurrent and effectively transmitting the pump-induced photoexcitation into deeper layers within the structure, beyond the penetration depth of the pump beam itself. In this manner, the effect of the modulation is not necessarily limited by the diffusion length of minority carriers created in the volume of pump light absorption.…”