Cu (In,Ga)Se2 thin films and solar cells prepared by selenization of metallic precursors

Abstract

CuIn(1−x)GaxSe2 (CIGS) thin films with Ga ratio, x, ranging from 0.55 to 0.75 were grown on Mo/glass substrates by the selenization of metallic precursors in a H2Se atmosphere. Without a postdeposition annealing step the films were found to have a highly graded composition that became Ga rich near the absorber/Mo interface. A high-temperature annealing step promoted diffusion of Ga to the surface region of the films. These absorbers were used to fabricate glass/Mo/CIGS/CdS/ZnO thin-film solar cells with open-circuit voltages ranging from 0.4 to 0.74 V and efficiencies approaching 12%. Devices, as well as the absorber layers, were characterized.

Crystallographic properties and elemental migration in two-stage prepared CuIn1−Al Se2 thin films for photovoltaic applications

“…This phenomenon is very similar to the observed segregation of Ga at the back of two-stage processed CIGS [21]. The most commonly suggested reason for this phenomenon is the relatively high temperature of formation of Ga selenides, compared to In selenides [21,22]. This hypothesis also applies to CIAS, since the only known selenide of aluminium is Al 2 Se 3 , which was reported to form at 480°C [23], against 221°C for the first In selenides.…”

Diffusion of indium and gallium in Cu(In,Ga)Se2 thin film solar cells

“…In many of the different CIGS fabrication techniques, an in depth variation of the Ga/(Ga þ In) ratio is introduced, intentionally or unintentionally. For example in the selenisation processes, the metals are first deposited and thereafter selenised to form CIGS, a higher Ga/(Ga þ In) ratio is spontaneously obtained towards the back contact [2]. In coevaporation processes a higher Ga/(Ga þ In) ratio towards the back contact is sometimes introduced intentionally by starting the deposition by evaporating pure CuGaSe 2 , or CIGS with a very high Ga content and then continue by evaporating CIGS with lower Ga content.…”

Use of diethylselenide for the preparation of CuInGaSe 2 films by selenization of metal precursors premixed with Se

“…When H 2 Se or elemental Se was used, In tended to diffuse toward the surface and Ga toward the substrate, giving rise to phase separation into CIS and CGS [3][4][5]11]. In this case, CIGS alloy was not formed although a variety of Se sources and stacking structures were attempted [3][4][5]11]. Marudachalam et al have proposed that phase separation might occur due to the difference in surface free energies and/or the difference in the reaction rates between the two phases [5].…”

“…These results are remarkably different from those reported for the selenization of Cu-In-Ga precursors using H 2 Se or elemental Se, as follows. When H 2 Se or elemental Se was used, In tended to diffuse toward the surface and Ga toward the substrate, giving rise to phase separation into CIS and CGS [3][4][5]11]. In this case, CIGS alloy was not formed although a variety of Se sources and stacking structures were attempted [3][4][5]11].…”