Theory of electroluminescence intensity and insights into recombination in thin film solar cells

Abstract

Equations describing the electroluminescence (EL) intensity as a function of material properties are derived for thin film solar cells and experimentally validated using Cu(In,Ga)Se2 solar cells. EL intensity at constant voltage is controlled by the electronic properties of the neutral bulk even when the diode current is controlled by recombination in the space charge region. Using a combination of techniques, it is found that recombination in the quasineutral bulk does not correlate with recombination in the space charge region. Differences between EL measurements on thin film cells and crystalline silicon cells are discussed including the effects of secondary barriers.

Analysis of recombination path for Cu(In,Ga)Se2 solar cells through luminescence

“…The coefficient into CIGS from ZnO film at forward bias, therefore, the provenance of EL spectra is also identified to be the CIGS layer [12]. Same as the estimation for PL, the width of EL collection is only 90 nm.…”

Electroluminescence intensity analysis of neutral bulk and space charge region collection effects on large-area CIGS module performance

“…One is from the neutral bulk region, and the other is from the SCR. By integrating the carrier recombination in both regions and ignoring reduction of the 978-1-4799-4398-2/14/$31.00 ©2014 IEEE actual bias across the absorber by any secondary barriers, the EL intensity as a function of the applied voltage (V) and the injected current (I) can be shown to have the following functional dependence when shunting can be neglected [4,6]:…”

“…(1) (2) Where n; is the intrinsic carrier concentration in the absorber, Le is the carrier collection length (which is the sum of the carrier diffusion length in the neutral bulk and the depletion width of the device) [4], k is Boltzmann's constant, q is the electron charge, T is the absolute temperature, and 1 is the nomadiative lifetime in the SCR.…”

“…Brown et at. derived equations describing the EL intensity as a function of the applied voltage and the injected current, and experimentally validated them using Cu(In,Ga)Se 2 (CIGS) solar cells [4]. They claimed that comparisons between the EL intensity of different cells at the same voltage are indicative of differences in the electronic properties of the neutral bulk even when the diode current is controlled by recombination in the Space Charge Region (SCR).…”

Testing and failure analysis of thin film solar cells

“…In this spectral range, a contribution from BBR cannot be excluded [23,24], so the two shapes are displayed for comparison in Fig. 3.…”