High rate (~7 nm/s), atmospheric pressure deposition of ZnO front electrode for Cu(In,Ga)Se₂ thin‐film solar cells with efficiency beyond 15%

Abstract

Undoped zinc oxide (ZnO) films have been grown on a moving glass substrate by plasma-enhanced chemical vapor deposition at atmospheric pressure. High deposition rates of~7 nm/s are achieved at low temperature (200°C) for a substrate speed from 20 to 60 mm/min. ZnO films are highly transparent in the visible range (90%). By a short (~minute) post-deposition exposure to near-ultraviolet light, a very low resistivity value of 1.6·10 À3 Ω cm for undoped ZnO is achieved, which is independent on the film thickness in the range from 180 to 1200 nm. The photo-enhanced conductivity is stable in time at room temperature when ZnO is coated by an Al 2 O 3 barrier film, deposited by the industrially scalable spatial atomic layer deposition technique. ZnO and Al 2 O 3 films have been used as front electrode and barrier, respectively, in Cu(In,Ga)Se2 (CIGS) solar cells. An average efficiency of 15.4 ± 0.2% (15 cells) is obtained that is similar to the efficiency of CIGS reference cells in which sputtered ZnO:Al is used as electrode.

Atmospheric Spatial Atomic Layer Deposition of In-Doped ZnO

“…Numerous methods for the deposition of ZnO films have been proposed, including thermal chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PE-CVD), temporal atomic layer deposition (ALD), magnetron sputtering, pulsed laser deposition, spray pyrolysis and sol-gel process. [2][3][4][5][6][7][8][9][10] The most common technology for the industrial deposition of doped ZnO films is sputtering. Low values of resistivity (∼4 10 −4 Ohm cm), high carrier mobility (∼50 cm 2 /V s) and high transparency in the visible range (>85%) have been achieved in doped ZnO films (e.g.…”

Highly conductive ZnO films with high near infrared transparency

“…In the following we investigate the optical and electrical properties of the representative b-ZnO and AZO films of comparable thickness (t ≈ 385 nm) and resistivity (ρ ≈ 1.05 · 10 −3 Ω cm) that were used in solar cell preparation experiments. All the film characteristics are summarized in Table I together with (Nevertheless, it is to be noted that the n e value of the nominally undoped ZnO reported here is the same [21] or even higher [24,25] than that of other highly conductive ZnO films in literature). At the other hand, the Hall mobility µ e of b-ZnO film is significantly higher…”

“…1(a). Indeed, it has been documented previously that the free carrier mobility is limited by grain boundary scattering, alongside the ingrain scattering mechanisms (e.g., ionized impurity scattering), in highly conductive SnO 2 [40] and ZnO [21,25] films.…”

“…However, the undoped ZnO films prepared by atmospheric pressure plasma-enhanced chemical vapor deposition (PECVD) and turned conductive by post-deposition exposure to near-ultraviolet light were recently reported as suitable to replace the AZO layer as a front electrode in Cu(InGa)Se 2 cells, if encapsulated by thin Al 2 O 3 overlayer [25].…”

Recent Advances in Atmospheric Vapor‐Phase Deposition of Transparent and Conductive Zinc Oxide

“…A minimum resistivity of ∼10 −2 Ω cm has been reported for as‐deposited ZnO:Al, which is still too high for using these films as transparent electrodes in electronic devices . Post‐deposition treatments, such as exposure to near‐UV radiation, have been used to reduce the resistivity of atmospheric PE‐CVD‐produced i ‐ZnO, allowing the use of these films as the front electrode in CIGS solar cells …”