Secondary barriers in CdS–CuIn1−xGaxSe2 solar cells

Abstract

Previous work on CdS–CuInSe2 (CIS) solar cells, which reported distortions of their current-voltage (J–V) curves under red illumination, is expanded in this work to include CdS–CuIn1−xGaxSe2 cells with variable Ga and CIS cells with variable CdS thickness. Different amounts of J–V distortion were observed in these cells under red light. The details are in good agreement with predictions of a photodiode model, in which a secondary barrier caused by the positive conduction-band discontinuity (spike) at the buffer–absorber interface is responsible for the current limitation. The illumination of the cell with high-energy photons lowers the barrier due to buffer photoconductivity, and thus removes the J–V distortion.

Non-Toxic Buffer Layers in Flexible Cu(In,Ga)Se2Photovoltaic Cell Applications with Optimized Absorber Thickness

“…The absorber works as a p-type doped area into a CIS and CIGS model with a typical thickness of 1-2 μm [5]. For the CIS absorber layer, the band gap is about 1 eV (0.98-1.04 eV) [6].…”

Enhancing the efficiency of SnS solar cells via band-offset engineering with a zinc oxysulfide buffer layer

“…V oc ), small FF, and low J sc . 33 This CBO discrepancy may be because of a variation of the SnS surface condition for different film thicknesses. Figure 3(b) shows the XRD spectra of SnS films grown on Mo layers as a function of SnS film thickness.…”

Solution-processed chalcopyrite–perovskite tandem solar cells in bandgap-matched two- and four-terminal architectures

“…It is also well known that due to the trapping and detrapping dynamics from defects in CdS high energy photons (2.4 eV and higher) shift the Fermi-level in CdS higher and thus increase the band bending in the absorber layer. 44,45 Under normal full-spectrum illumination this upward shift in the Fermi-level in the CdS (and increased band bending in the absorber) is typically enough to allow photo-generated electrons to cross the barrier. However, since the high energy portion of the light up to 800 nm -for a FAPbI3 perovskite -will be absorbed by the top cell, this is problematic for some CIS cells in tandem devices.…”

“…This drop in fill-factor may be explained by considering: (1) the barrier height for photo-generated electrons in the absorber layer to cross over into the buffer layer, commonly referred to as a positive conduction band offset or "spike," 43,44 and (2) the kinetic energy that the photo-generated electrons have as a result of acceleration from the built-in electric field in the absorber. Any increase in the height of the barrier or decrease in the electron kinetic energy due to a decrease in band bending may cause a serious loss in fill factor.…”