= 아 래 =
1. 일 시 : 2012. 11. 13 (화), 16:00 ~
2. 장 소 : 응용공학동 1층 영상강의실
3. 연 사 : 김기환 박사 (University of Delaware)
4. 제 목 : Metal precursor reaction for Cu(Ga,In)(Se,S)2 (CIGSS) absorber layer with controlled Ga composition
A growing interest in manufacturing large-area CuInGaSe2 (CIGS, when S included, CIGSS) solar cells has been leading significant progresses in the reaction of metal precursors in Se- and/or S- containing atmospheres. This reaction must address two critical issues: Ga accumulation near the back contact which reduces the expected Voc indevices, and poor adhesion at the Mo/CIGSS interface. A two-step process with partial reactionin H2Se followed by reaction at high temperature in H2S has shown promise but the process window for optimization without adhesion problems is narrow. This talk describes a three-step H2Se/Ar/H2S reaction to give device-quality CIGSS absorbers with controlled Ga composition, enhanced grain size and adhesion. First, metal precursors prepared by co-sputtering were selenized at 400 for 60 min (1st selenization) and then annealed in Ar at 550 C for 20 min (2nd Ar anneal). Finally, the films were sulfurized in H2S at 550 for 10 min (3rd sulfurization). Detailed characterization will describe the film evolution over these process steps including the film microstructure, phases determined by XRD, and through-film composition after each stage of the reaction. The idea of this method is to induce recrystallization with Ga homogenization during the 2nd Ar anneal step. In order to doing so, the 1st selenization step should assure a fine microstructure with an unreacted Cu-Ga intermetallic. The Ga homogenization and large grain size obtained from the 2nd Ar anneal were not significantly affected by the 3rd sulfurization step except for a small S incorporation near the CIGSS surface. The reacted films after the 3rd sulfurization also exhibited good adhesion. Finally, CIGSS solar cells with 3-step H2Se/Ar/H2S reaction were fabricated and the best device efficiency was as high as 16.1% with VOC of 647 mV. In addition, some further applications using the 3-step H2Se/Ar/H2S reaction will be discussed in this talk.