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Influence of the transition region between p-and n-type polycrystalline silicon passivating contacts on the performance of interdigitated back contact silicon solar cells

: Reichel, C.; Müller, R.; Feldmann, F.; Richter, A.; Hermle, M.; Glunz, S.W.


Journal of applied physics 122 (2017), No.18, Art. 184502, 10 pp.
ISSN: 0021-8979
ISSN: 1089-7550
Journal Article
Fraunhofer ISE ()
Solarzellen - Entwicklung und Charakterisierung; Photovoltaik; Silicium-Photovoltaik; Neuartige Photovoltaik-Technologien; Charakterisierung von Prozess- und Silicium-Materialien; Dotierung und Diffusion; Herstellung und Analyse von hocheffizienten Solarzellen

Passivating contacts based on thin tunneling oxides (SiOx) and n- and p-type semi-crystalline or polycrystalline silicon (poly-Si) enable high passivation quality and low contact resistivity, but the integration of these p+/n emitter and n+/n back surface field junctions into interdigitated back contact silicon solar cells poses a challenge due to high recombination at the transition region from p-type to n-type poly-Si. Here, the transition region was created in different configurations—(a) p+ and n+ poly-Si regions are in direct contact with each other (“pn-junction”), using a local overcompensation (counterdoping) as a self-aligning process, (b) undoped (intrinsic) poly-Si remains between the p+ and n+ poly-Si regions (“pin-junction”), and (c) etched trenches separate the p+ and n+ poly-Si regions (“trench”)—in order to investigate the recombination characteristics and the reverse breakdown behavior of these solar cells. Illumination- and injection-dependent quasi-steady state photoluminescence (suns-PL) and open-circuit voltage (suns-Voc) measurements revealed that non-ideal recombination in the space charge regions with high local ideality factors as well as recombination in shunted regions strongly limited the performance of solar cells without a trench. In contrast, solar cells with a trench allowed for open-circuit voltage (Voc) of 720 mV, fill factor of 79.6%, short-circuit current (Jsc) of 41.3 mA/cm2, and a conversion efficiencies (η) of 23.7%, showing that a lowly conducting and highly passivating intermediate layer between the p+ and n+ poly-Si regions is mandatory. Independent of the configuration, no hysteresis was observed upon multiple stresses in reverse direction, indicating a controlled and homogeneously distributed breakdown, but with different breakdown characteristics.