On the recombination behavior of p⁺-type polysilicon on oxide junctions deposited by different methods on textured and planar surfaces

Abstract

We investigate the passivation quality of hole‐collecting junctions consisting of thermally or wet‐chemically grown interfacial oxides, sandwiched between a monocrystalline‐Si substrate and a p‐type polycrystalline‐silicon (Si) layer. The three different approaches for polycrystalline‐Si preparation are compared: the plasma‐enhanced chemical vapor deposition (PECVD) of in situ p+‐type boron‐doped amorphous Si layers, the low pressure chemical vapor deposition (LPCVD) of in situ p+‐type B‐doped polycrystalline Si layers, and the LPCVD of intrinsic amorphous Si, subsequently ion‐implanted with boron. We observe the lowest J0e values of 3.8 fA cm−2 on thermally grown interfacial oxide on planar surfaces for the case of intrinsic amorphous Si deposited by LPCVD and subsequently implanted with boron. Also, we obtain a similar high passivation of p+‐type poly‐Si junctions on wet‐chemically grown oxides as well as for all the investigated polycrystalline‐Si deposition approaches. Conversely, on alkaline‐textured surfaces, J0e is at least 4 times higher compared to planar surfaces. This finding holds for all the junction preparation methods investigated. We show that the higher J0e on textured surfaces can be attributed to a poorer passivation of the p+ poly/c‐Si stacks on (111) when compared to (100) surfaces.

Implantation‐based passivating contacts for crystalline silicon front/rear contacted solar cells

“…Because our p‐type poly‐Si layer for textured surface is still under development, we locate the hole contact at rear side on a flat interface. The choice of rear‐emitter architecture additionally improves the transport of minority carriers inside c‐Si bulk as discussed by Larionova et al and Bivour et al for the case of silicon heterojunction solar cells. Only the front side of the c‐Si wafer is textured (see Figure A), by covering the other side with 100‐nm‐thick SiN x protective layer.…”

Passivating contacts for crystalline silicon solar cells

“…The current state-of-the-art polysilicon contacts can be implemented via a range of different deposition and doping techniques, exhibiting J0c < 5 fA.cm 2 and ρc < 2 mΩcm 2 for both n-type and p-type contacts. 24,69,70 At the device level, a particularly promising hybrid structure, being developed by several groups, is shown in Fig. 4b which features a full-area n + poly-Si rear contact and a boron diffused front hole contact.…”

Conductivity and Surface Passivation Properties of Boron‐Doped Poly‐Silicon Passivated Contacts for c‐Si Solar Cells

“…A promising way to develop the poly‐Si/SiO x structure relies on the deposition of hydrogen‐rich amorphous silicon (a‐Si:H) by plasma enhanced chemical vapor deposition (PECVD), followed by an annealing step required to crystallize the a‐Si:H layer into poly‐Si . The PECVD approach enables to deposit the poly‐Si layer on a single side of the wafer, contrarily to Low Pressure CVD technique that involves a deposition on both sides of the wafer .…”

“…Blister‐free layers can be deposited without addition of carbon, as reported in ref. . However, a detailed study of the interplay between process parameters and blistering has not been undertaken yet.…”

“…[1] A promising way to develop the poly-Si/ SiO x structure relies on the deposition of hydrogen-rich amorphous silicon (a-Si:H) by plasma enhanced chemical vapor deposition (PECVD), followed by an annealing step required to crystallize the a-Si:H layer into poly-Si. [2][3][4][5][6] The PECVD approach enables to deposit the poly-Si layer on a single side of the wafer, contrarily to Low Pressure CVD technique that involves a deposition on both sides of the wafer. [7][8][9] However, if not optimized, PECVD of a-Si: H layer on top of SiO x involves a blistering of the layer due to its high hydrogen (H) content which causes a severe degradation of the poly-Si layer after annealing.…”