Hydrogen plasma treatment of ZnO-coated TCO films

Abstract

Hydrogen plasma treatment of textured Sn0,:F TCO (transparent conductive oxide) films coated with ZnO layer of lOOA in thickness was investigated for high efficiency a-Si solar cells. It was found that ZnO over-layered structure was effective to improve the hydrogen plasma durability. Furthermore, it was shown that the resistivity of over-layered "CO films decreased dramatically after the hydrogen plasma treatment at a temperature of 300°C without any change in optical transmission. The decrease in resistivity was due to the sufficient increase in Hall mobility, which was caused by the elimination of chemical reduction. After the hydrogen plasma treatment under the optimized condition, the highest Hall mobility of 70 cm2/V.sec, sheet resistance below 5 n l s q . and optical transmission above 85% were attained.

Potential-induced degradation: a challenge in the commercialization of perovskite solar cells

“…ZnO is significantly less susceptible to chemical attack by atomic hydrogen compared to the SnO 2 -based TCO layer. 122 Accordingly, the thin-film solar modules that utilized a ZnO-based TCO layer did not exhibit any noticeable delamination effects. 16,114…”

Optimization of Processing and Modeling Issues for Thin Film Solar Cell Devices Including Concepts for The Development of Polycrystalline Multijunctions: Annual Report; 24 August 1998-23 August 1999

“…The SnO 2 is chemically reduced, leaving a thin but highly absorbing Sn-rich layer [12,13,14]. It has been reported that degradation can be minimized or even eliminated by using low substrate temperatures [14,15], at faster a-Si growth rates [15], or by covering the SnO 2 with a thin protective sputtered ZnO:Al layer [16,17,18]. The ZnO properties are relatively inert to H 2 plasma damage [14,15] although the H 2 penetrates several hundred Angstroms into the ZnO [15,19] and increases its bandgap (8).…”

“…One of the leading SnO 2 manufacturers, Asahi Glass, has shown that the optical transmission of their SnO 2 is not degraded by H 2 plasma over the range from 100 to 300°C [21], in direct contradiction to results from other groups, as well as their own later work [16]. Some groups find that a thin ZnO layer does not protect the SnO 2 [22,23].…”

“…This is discussed further below. Our previous studies [16] of stressing devices on SCI CdTe material with IEC's wet or dry contact process at V oc (unbiased) indicated that V oc degraded 0.1-0.2 V over 5-6 days. This was observed on devices which received a wide range of contact processing at IEC.…”

“…The ZnO thicknesses were chosen to trade-off the optical losses with the protective abilities. A ZnO layer of 60 nm was thought to be sufficiently thick to prevent any plasma interaction with the SnO 2 but has 1-2% absorption beyond 500 nm: whereas a layer of 20 nm has negligible absorption losses but its ability to protect the SnO 2 was unknown since H can penetrate several hundred Angstroms through sputtered ZnO [16,20]. The effect of H 2 plasma substrate temperature or Si film growth on SnO 2 sheet resistance, mobility and carrier concentration are shown in Figure 3.9, Figure 3.10, and Figure 3.11, respectively.…”