Electronic properties of grain boundaries in Cu(In,Ga)Se2 thin films with various Ga-contents

Abstract

We present a study on the electronic properties of grain boundaries (GBs) in polycrystalline Cu(In,Ga)Se 2 (CIGSe) thin films. As grown as well as KCN-treated films were comparatively investigated. No influence of the chemical treatment on the electronic properties of GBs was found. GBs in general exhibited a large variation of their electronic properties. By means of a novel method of data analysis, both potential barriers for holes and electrons were found at GBs, in a range from-118mV to +114mV, as well as uncharged GBs. No dependence of the electronic GB-properties on the Ga-content was found. Consequently we therefore conclude that there is no correlation between electronic GB-properties and the obtained maximum efficiencies of CIGSe thin film solar cells as a function of the Ga-content.

High photo-conversion efficiency in double-graded Cu(In,Ga)(S,Se)2thin film solar cells with two-step sulfurization post-treatment

“…Baier et al . reported that the work function of an as‐grown (1 h exposed to air) CIGS sample was ~4.4 eV, and that of a chemically etched CIGS sample was ~4.8 eV . Our work function value for the CIGSSe samples averaged ~4.72 eV with deionized water etching, and this corresponds to the values presented by the other groups.…”

“…We should mention that Ga and S influenced the work function of the CIGSSe thin films. In a previous study, the work function of GBs in CIGSe absorber layer did not depend on Ga content . However, a correlation between the work function and S/(S + Se) composition ratio of Cu 2 ZnSn(S,Se) 4 (CZTSSe) was observed in KPFM measurements .…”

“…The work functions of the two‐step‐sulfurized CIGSSe thin films with different sulfur concentrations were calculated by comparing the work functions of the tip and the sample. The work function of the sample (ϕ sample ) was obtained by subtracting the tip work function (ϕ tip ) and by using highly‐oriented pyrolytic graphite , though its value is affected by the doping and carrier concentration . V CPD is the contact potential difference of the tip and the sample, and e is the elementary charge.…”

“…Kelvin probe force microscopy (KPFM) was used to characterize the phase of the sample surface, and further imaging was performed using an atomic force microscope (AFM) (n‐Tracer, NanoFocus Inc., Seoul, Korea) with a cantilever with Pt/Ir‐coated silicon tips (Nanosensor). The tip was calibrated with highly‐oriented pyrolytic graphite (Ф = 4.6 ± 0.1 eV) to convert the potential difference to a workfunction and an absolute workfunction of the tip. The AFM topographical images were obtained at a probe resonant frequency of 78.18 kHz, and the surface potential was measured in the non‐contact mode by applying an AC voltage with amplitude of 1.0 V and a frequency of 60.5 kHz to obtain clear images with sufficient sensitivity.…”

Carrier transportation in polycrystalline CuInSe2 thin films with Cu-deficient grain boundaries

“…In Cu , it can be seen that the electronic structures at GBs are significantly influenced by the defects. A recent experimental study [26] on electronic properties of GBs in polycrystalline Cu(In,Ga)Se 2 thin films may confirm the results. The thin films were studied by a Kelvin probe force microscopy in an ultrahigh vacuum (UHV) environment.…”