Firing-Stable PECVD SiO_xN_y/n-Poly-Si Surface Passivation for Silicon Solar Cells

Abstract

Passivating contacts based on SiO x /poly-Si exhibit excellent contact and surface passivation properties enabling very high solar cell conversion efficiencies. In this paper, we investigate and optimize the plasmaenhanced chemical vapor deposition (PECVD) of SiO x N y /n-a-Si stacks, their subsequent annealing to SiO x N y /n-poly-Si stacks followed by PECVD SiN x deposition and firing. We eliminate blistering of the poly-Si layer by enabling a controlled hydrogen out-diffusion during the annealing step. Whereas the J 0 of thermal SiO x /n-poly-Si stacks degrade after firing, PECVD SiO x N y /n-poly-Si stacks exhibit excellent firing stability enabling J 0 values down to 1.3 fA/cm 2 after firing which corresponds to an outstanding implied V OC of 744 mV. The application of different hydrogenation processes to the thermal SiO x /n-poly-Si and PECVD SiO x N y /n-poly-Si stacks reveals that both stacks achieve excellent passivation properties with J 0 = 1.5 fA/cm 2 after maximum hydrogenation. However, only the PECVD SiO x N y /n-poly-Si stack maintains this excellent surface passivation after firing possibly due to a superior capability to retain the hydrogen at the c-Si/SiO x N y interface during firing and thus demonstrates the potential as a future manufacturing process sequence.

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

“…A further supporting argument for the hypothesis of an important role of mechanical stress for the degradation of POLO junction upon firing is the recent observation of Stöhr et al 49 that junctions with a PECVD-SiO z N y -based interfacial oxide-whose thermal expansion coefficient (2.2-2.6 Â 10 À6 /K), 50 depending on the deposition parameters, can be much closer to that of (poly-)Si than that of thermally grown SiO z -show a significantly improved firing stability.…”

“…These results allow further optimization of the passivation quality of POLO junction after firing, which includes the choice of dielectric capping layers and an adjustment of the firing belt speed. In addition, the choice of an intermediate layer with a higher thermal expansion coefficient, which is, therefore, more suitable with c‐Si and poly‐Si, such as SiN y O x , 49 can be selected to increase the firing stability. However, this layer must also provide a good contact resistance.…”

Comparison of firing stability between p‐ and n‐type polysilicon passivating contacts

“…The firing stability of n‐type poly‐Si passivating contacts has been studied by a number of research groups 11–18 . In our recent work, 19 a pronounced surface degradation was observed on n‐type ex‐situ phosphorus‐doped poly‐Si contacts fired either with or without the presence of SiN x capping layers at above 800°C, with the degradation extent depending on various processing parameters, such as the growth of interfacial SiO x , the poly‐Si deposition temperature, the phosphorus diffusion conditions, and the dielectric capping layer.…”

“…[9][10][11] The firing stability of n-type poly-Si passivating contacts has been studied by a number of research groups. [11][12][13][14][15][16][17][18] In our recent work, 19 a pronounced surface degradation was observed on n-type ex-situ phosphorus-doped poly-Si contacts fired either with or without the presence of SiN x capping layers at above 800 C, with the degradation extent depending on various processing parameters, such as the growth of interfacial SiO x , the poly-Si deposition temperature, the phosphorus diffusion conditions, and the dielectric capping layer. In other work, 20 we proposed a hypothesis that an excessive amount of hydrogen released from the dielectric capping layer to the poly-Si/ SiO x structure, particularly surrounding the interfacial SiO x , causes the degradation after firing.…”

Effects of Chamber Pressures on the Passivation Layer of Hydrogenated Nano-Crystalline Silicon Mixed-Phase Thin Film by Using Microwave Annealing

“…The annealing process plays a crucial role in obtaining a high carrier lifetime in the hydrogenation from the film to the c-Si surface. Some studies related to post-annealing have been reported [26][27][28][29][30]. Microwave annealing (MWA) is a new and effective method to obtain high-carrier-lifetime thin films.…”