Solar Frontier K.K. have been working on the research of Se-free Cu(In,Ga)S2 (CIGS) solar cells, and the best Eff reached 15.5% (confirmed by Fraunhofer ISE) [1]. As a next step to enhance the efficiency (Eff), we are considering adding Ag to Se-free CIGS. In this paper, we investigated the possibility of Se-free (Ag,Cu)(In,Ga)S2 (ACIGS) solar cells and revealed the addition effect of Ag. Table 1 shows the composition of the precursors for sample A, B, C and D. Sample A has no Ag, on the other hand, the other samples have Ag whose amount is 0.37~1.13μmol/cm2. Figure 1 shows the SEM images of sulfurized films. The morphology of the absorbers is very different, and the more Ag amount the precursors have, the larger grains the absorbers have. It is supposed that the high ratio of (Ag+Cu)/(Ga+In) helped the crystal growth during sulfurization. However, the Se-free ACIGS device demonstrated lower Eff compared with the Se-free CIGS device as shown in Fig. 2. It is assumed that the metal depth-profile and composition ratio of absorbers were not optimized yet. We will present the further improvement of Se-free ACIGS solar cells at the conference.
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