Junction and Device Formation Using CdS

The first device with CuInSe2 high-performance solar cells was a heterojunction cell between p-type single-crystal CuInSe2 and a thin film of и-type CdS (Wag­ner et al. 1974; Shay et al. 1975). Consequently, most later thin film junction were formed by depositing CdS onto the CuInSe2 films (Kazmerski et al. 1978), indi­cating that a similar mechanism as discussed in earlier chapters occurred in CdS to improve the efficiency. Later, an undoped layer of CdS, followed by CdS doped with in Michaelson (1972). Further improvement was achieved by replacing the doped CdS with doped ZnO (Potter et al. 1985). The undoped CdS layer adjacent to the Cu(InGa)Se2 film was reduced in thickness to ~50 nm to maximize the optical transmission.

A pinhole-free coating of the thin CdS layer can be obtained by chemical bath deposition, also referred to as solution growth. The thin CdS layer grows ion-by­ion, resulting in dense homogeneous films (Lincot et al. 1993) with mixed cu – bic/hexagonal or predominantly hexagonal lattice structure (Wada 1997; Lincot

et al. 1993; Nakada and Kunioka 1999). The films consist of crystallites with a grain size of the order of tens of nanometers (Lincot et al. 1993).

Deviation from stoichiometry of CdS is commonly observed: films tend to be cadmium-rich and contain substantial amounts of oxygen, hydrogen, carbon and nitrogen (Kylner et al. 1996a; Hashimoto et al. 1998).

Updated: August 23, 2015 — 10:59 pm