Boron Doped diamond films as electron donors in photovoltaics: An X-ray absorption and hard X-ray photoemission study

Abstract

Highly boron-doped diamond films are investigated for their potential as transparent electron donors in solar cells. Specifically, the valence band offset between a diamond film (as electron donor) and Cu(In,Ga)Se 2 (CIGS) as light absorber is determined by a combination of soft X-ray absorption spectroscopy and hard X-ray photoelectron spectroscopy, which is more depthpenetrating than standard soft X-ray photoelectron spectroscopy. In addition, a theoretical analysis of the valence band is performed, based on GW quasiparticle band calculations. The valence band offset is found to be small: VBO ¼ VBM CIGS-VBM diamond ¼ 0.3 eV 6 0.1 eV at the CIGS/ Diamond interface and 0.0 eV 6 0.1 eV from CIGS to bulk diamond. These results provide a promising starting point for optimizing the band offset by choosing absorber materials with a slightly lower valence band maximum. V

Development and Application of a Multifunctional Nanoindenter: Coupling to Electrical Measurements and Integration In-Situ in a Scanning Electron Microscope

“…In that case, the electrical contact conductance evolves as a power-law of contact radius [29,1]. In the present case, the mean free path of electrons in this highly-doped diamond tip is estimated to be circa 2 nm [30,31,32], which is in good agreement with the present transition depth.  Multi--spots model: Based on Holm's approach [1], it has been shown that if a macroscopic contact is the combination of a large number of local spots (because of roughness, surface contamination, native oxide,…), the total contact conductance is the sum of the individual conductances with an additional term accounting for the spot interaction.…”

Recent applications of hard x-ray photoelectron spectroscopy

“…It can be seen from the inset in Figure 17 that a simple linear extrapolation would produce an erroneous valence-band maximum that is several eV lower than that determined by this procedure. HAXPES and Kraut's method have been used for band-alignment measurements of many materials systems, including Pt and Ag contacts on diamond for high-flux beamline monitors [82], Pt/BaTiO 3 /Cr film stacks for ferroelectric tunnel junctions [83], Ge/high dielectric constant oxide interfaces [84,85], and diamond/Cu(InGa)Se 2 [86] and poly(3-hexylthiophene-2,5-diyl)/ZnO [87] interfaces for applications in photovoltaics.…”

Accurate determination of the valence band edge in hard x-ray photoemission spectra using GW theory

“…This greatly reduces the surface sensitivity (from which photoemission spectroscopy at lower photon energies suffers) and makes the study of interfaces buried 100 Å or more below the surface possible. Because of these advantages, HXPS is becoming an increasingly popular technique for the experimental determination of valence-band offsets 12,13 . However, at such high photon energies, matrix element effects can play a crucial role and can cause significant errors in valence-band offsets determined using standard methods, as we will show below.…”

“…Instead of fitting a theoretical model to the experimental spectrum in the vicinity of the valence-band edge, we align the sharpest peak in the valence-band region of the experimental spectrum with the corresponding feature in a theoretical VB DOS curve of the quasiparticles from a GW theory calculation. We apply our method to hydrogen-terminated boron-doped diamond (HBD), which is a promising substrate material in novel solar cell devices [13][14][15] . We further verify the accuracy of the new method by carrying out measurements with variable light polarizations 16 .…”