Development of rear surface passivated Cu(In,Ga)Se2 thin film solar cells with nano-sized local rear point contacts

Potential‐induced optimization of ultra‐thin rear surface passivated CIGS solar cells

“…This is most probably due to a lack of Na in the CIGS absorber layer, as can be seen from the "roll-over" effect shown in the J-V curve; see Fig. 1(b) and [4,5]. It is indeed known that this Al 2 O 3 passivation layer is an effective barrier layer for Na diffusion [10].…”

“…As shown in [4][5][6], these ultrathin ungraded CIGS absorber layers with uniform low Ga concentration are exemplary characterization devices to assess rear surface passivation and rear internal reflection. Next, the buffer layer is deposited using a standard CBD [4][5][6].…”

“…Next, the buffer layer is deposited using a standard CBD [4][5][6]. Note that the unpassivated reference cells have the same processing sequence, but without the formation of the advanced rear passivation structure (steps 3-5 in Table 1).…”

“…On the other hand, the Al 2 O 3 rear surface passivation leads to a reduction in interface recombination at the rear of CIGS solar cells (rear-contact/absorber-layer). It consists of an Al 2 O 3 film with nano-sized point openings between the rear contact and the CIGS absorber layer, which results in a reduction of interface recombination by chemical (a reduction in interface trap density) and field-effect passivation (a reduction in surface minority charge carrier concentration), while the point openings allow for contacting [4][5][6].…”

“…Hence, the Al 2 O 3 passivation layer is a physical barrier for Na and consequently limits Na diffusion from the SLG to the CIGS absorber layer. Therefore, additional Na provided by a NaF precursor layer is required for the rear passivated solar cells [4,5]. However, it occasionally happens that the NaF layer is too thin resulting in underperforming rear passivated cells, due to a lack of Na as apparent by J-V curves with characteristic "roll-over" effects [4,5].…”