The effect of copper on the sub-bandgap density of states of CdTe solar cells

Abstract

Two optical sub-bandgap transitions in CdTe thin-film solar cells have been identified using detailed transient photocapacitance and transient photocurrent spectroscopy measurements. A broad response centered at EV + 0.9 eV directly correlates with the quantity of Cu present in the absorber layer, while a second response at EV + 1.2 eV does not depend on Cu or Zn and may be an intrinsic defect. These results demonstrate the influence of Cu on the sub-bandgap density of states of CdTe, and they are critical to understanding, modeling, and improving its optoelectronic properties.

Band Tailing and Deep Defect States in CH3NH3Pb(I1–xBrx)3 Perovskites As Revealed by Sub-Bandgap Photocurrent

“…Urbach energies from CH 3 NH 3 Pb(I 1−x Br x ) 3 perovskites in this study are shown as red squares, and those from literature data are shown as blue triangles. 11,14 Also shown are a range of technologically important semiconductors (black dots): CZTSSe (Se-rich Cu 2 ZnSn(S,Se) 4 ),20 Si, 10 CIGS (Cu(In,Ga)Se 2 ),19 InP,29 GaAs, 30 CdTe,31 CZTS (S-rich Cu 2 ZnSnS 4 ),20 CGS (CuGaSe 2 ), 32 a-Si, 33 a-SiC:H,34 Al 0.05 In 0.95 N,35 and In x Ga 1−x N (In-rich, graded In profile).36…”

CdTe Photovoltaics in Superstrate Geometry–Back-Contact Materials: A Review

“…Warren et al reaffirmed the results with the time-of-flight secondary-ion mass spectrometry (SIMS). 56 When the amount of Cu exceeds the threshold level, it leads to the formation of substitutional complexes Cu Cd − and interstitial defect Cu i 2+ , which have been reported many times previously. The diffusion of Cu creates defects leading to crossover by reducing the lifetime of photogenerated charge carriers.…”

“…The greater concentration of Cu Cd will improve the hole concentration and hence the p-type conductivity of the CdTe device. Warren et al reaffirmed the results with the time-of-flight secondary-ion mass spectrometry (SIMS) …”

Increased Optoelectronic Quality and Uniformity of Hydrogenated p-InP Thin Films

“…Values reported for CIGS, range from 18 to 26 meV, for CdTe from 15 to 25 meV, and for CZTS from 13 to 31 meV. [27][28][29][30] At energies below the bandtail, the spectra of both samples are well fitted by the sum of two defect transitions occurring at 0.64 and 1.10 eV. For the sample without hydrogenation, the defect transition at 1.10 eV dominates the sub-gap absorption.…”

“…TPI spectroscopy, a form of sub-gap absorption spectroscopy, was used to characterize the energetic distribution of optically active defects in the band gap of TF-VLS InP photovoltaic devices. 27,28 In order to measure a TPI spectrum, a current transient was produced by holding the sample in reverse bias (-0.5 V) following a 100 ms filling pulse (+0.2 V). The samples were illuminated with monochromatic light during every other transient, and the TPI signal was calculated from the integrated difference between the illuminated and nonilluminated transients.…”