STRUCTURE AND CHEMISTRY OF CUINSE2 FOR SOLAR-CELL TECHNOLOGY - CURRENT UNDERSTANDING AND RECOMMENDATIONS

The results of a workshop on the structure and chemistry of CuInSe2, ( CIS), held in Jackson Hole, WY (USA), are presented. The participants are the authors of this paper. Issues in CIS properties and device per formance were divided into those dominating common CIS and those relev ant to the best CIS. Common CIS is non-equilibrium material containing numerous lattice defects and second phases surrounding the grains or segregated to the surface. Common CIS is capable of producing solar ce lls yielding in excess of 10% conversion efficiency provided that ther e is no CuxSe present. The best physical vapor deposited (PVD) CIS is formed at high temperatures, where rapid segregation should minimize t he incorporation of dissolved point defects. This CIS has relatively l arge, strongly (112)-oriented, nearly perfect grains. Growth of the ma jority of the film under strongly Cu-rich conditions provides the best results, although the final film must be free of CuxSe phases. The di fferences between common CIS and the best CIS are relatively process-i ndependent (but process-variable-dependent) and tend to limit the open -circuit voltage and fill factor of devices. The workshop consensus re commendations were as follows. The selenization reaction must be studi ed to determine how desirable properties, reproducibly demonstrated in PVD CIS, can be reliably achieved. Controlled experiments should be c arried out to determine the effect of extrinsic doping and grain bound aries on minority carrier lifetimes. Finally, a mechanism is needed fo r analysis of films to show how materials produced by different method s compare.