Reduction of Cu-rich interfacial layer and improvement of bulk CuO property through two-step sputtering for p-CuO/n-Si heterojunction solar cell

Abstract

Copper-rich interfacial-layer (Cu-rich IL) is formed during sputter deposition of cupric oxide (CuO) layer on silicon (Si). It has significant impact on the performance of p-CuO/n-Si heterojunction solar cells. In this report, CuO films deposited on Si at different RF-power levels using single and two-step RF-sputtering techniques and p-CuO/n-Si heterojunction solar cells have been investigated. Systematic characterization using XPS, AFM, XRD, Raman, and HR-TEM reveal that two-step RF-sputtering technique offers better crystal quality CuO film with thinner Cu-rich IL layer. Photovoltaic (PV) properties with an open-circuit voltage (Voc) of 421 mV, short circuit current (Jsc) of 4.5 mA/cm2, and a photocurrent of 8.3 mA/cm2 have been achieved for the cells prepared using two-step sputtering method, which are significantly higher than that for the solar cells fabricated using a single-step sputtering. The PV properties were further improved by depositing CuO films at higher working pressure with nitrogen doping. The efficiency of the best device achieved is approximately 1.21%, which is the highest value reported for p-CuO/n-Si heterojunction based solar cells.

Titanium doped cupric oxide for photovoltaic application

“…3 presents Raman spectra of CuO and CuO(Ti) thin films with various Ti concentrations after annealed at 300°C for 1 min. The distinct peaks, observed at $ 125, 288 and 599 cm À 1 indicate the formation of CuO [5,6]. The intensity of all the Raman peaks does not significantly change with increasing Ti concentration from 0% to 0.099%, further confirming that good crystallinity is retained in the case of lightly doped samples.…”

“…However, as shown in this figure, the performance of the highly doped CuO(Ti) is significantly degraded because of the high recombination rate with the CuO layer. As reported elsewhere [5,6], the formation of Cu rich interfacial layer and amorphous like isolation layer between copper oxide absorber layer and Si substrate degrades the interface properties at p-CuO/n-Si heterojunction and may intensify the Fermi level pinning effect, which results in large leakage current and low V oc . Formation of interfacial insulation layer is mainly due to the residual oxygen in the sputter chamber and it is also observed for sputter grown beta-phase iron silicide based solar cells [14][15][16].…”

“…The crosssectional TEM images of the p-CuO(Ti)/n-Si devices show the formation of a thin Cu rich (Cu x O, x41) interfacial layer at CuO(Ti)/Si interface. The formation of Cu rich interfacial layer depends on sputtering conditions used during the deposition, which has been reported elsewhere [6].…”

“…The issues related to the formation of interfacial insulation layer and Cu-rich interfacial layer were addressed by a two-step sputtering technique at high working pressure [6]. In two-step sputtering technique, at first, thin layer of CuO was deposited on n-Si substrate at high working pressure of 30 mTorr and low sputtering power of 50 W to reduce the thickness of both amorphous like isolation layer and Cu-rich interfacial layer.…”

“…It exhibits high optical absorption and ideal band gap of $ 1.4 eV for the solar light absorption in the whole visible spectral region [3,4]. However, despite the predicated theoretical conversion efficiency of 31%, the highest reported conversion efficiency is only around 1% [5,6].…”