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Carrier-selective passivating contacts have been demonstrated to be crucial to reach the practical efficiency limit of single junction, crystalline silicon (c-Si) based solar cells. Yet, the electrical transport losses affecting the collection of photogenerated carriers remain to be addressed. To this aim, different methodologies and characterization techniques are currently used. In this contribution, we propose the concept of shell as a new terminology to describe carrier-selective passivating contacts. Then, we present a novel characterization methodology using transfer length method (TLM) measurement under variable illumination to investigate the charge-carrier transport in amorphous/crystalline silicon heterojunction (SHJ) n-type contact stacks. We use technology computer-aided design simulation to model a TLM structure and to identify the physical phenomena and the key parameters affecting the contact resistivity (ρ c) and the charge carrier accumulation of such contact stacks. Then, the simulation results are compared with experimental data by performing variable-illumination TLM measurements of actual SHJ n-type contact stacks. Specifically, we demonstrate that illumination has a strong impact on the measured ρ c value, highlighting the importance of measuring ρ c under maximum power point conditions for a relevant characterization of solar cell transport losses. In addition, we investigate the dependence of ρ c to a change in the injected carrier density within the c-Si bulk to compare the illumination responses of different SHJ n-type contact stacks. In the quest for maximal efficiency, this method may insightfully complete other characterization techniques to further understand and study the electrical transport in solar cells. [ABSTRACT FROM AUTHOR]

Highlights • An innovative back-contacted c-Si solar cell using a tunnel junction is reported. • Nano-crystalline silicon layers are the key enablers of this new device. • Up to 23.9% conversion efficiency is demonstrated. Abstract This paper reports on the development of an innovative back-contacted crystalline silicon solar cell with passivating contacts featuring an interband tunnel junction at its electron-collecting contacts. In this novel architecture, named "tunnel-IBC", both the hole collector patterning and its alignment to the electron collector are eliminated, thus drastically simplifying the process flow. However, two prerequisites have to be fulfilled for such devices to work efficiently, namely (i) lossless carrier transport through the tunnel junction and (ii) low lateral conductance within the hole collector in order to avoid shunts with the neighboring electron-collecting regions. We meet these two contrasting requirements by exploiting the anisotropic and substrate-dependent growth mechanism of n- and p-type hydrogenated nano-crystalline silicon layers. We investigate the influence of the deposition temperature and the doping gas concentration on the structural and the selectivity properties of these layers. Eventually, tunnel-IBC devices integrating hydrogenated nano-crystalline silicon layers demonstrate a conversion efficiency up to 23.9%. [ABSTRACT FROM AUTHOR]

This work presents the upscaling of the tunnel IBC technology on large area, Czochralski (Cz) n-type wafers. At the junction level, a self-aligned PECVD masking technology has been developed for the deposition of hydrogenated nano-crystalline silicon (nc-Si:H) layers on industrial 6-inch pseudo-square wafers. This damage free patterning technology allows state-of-the-art passivation with a minority carrier lifetime of 9 ms at an injection level of 1015 cm-3, thus enabling extremely long diffusion lengths up to several millimetres. The use of indium-free, cost effective aluminium-doped zinc oxide strongly reduces the materials bill of the tunnel-IBC technology while maintaining very low contact resistance for both the electron and the hole contacts. Remarkably, these tunnel-IBC devices demonstrated a conversion efficiency of 25% on large area (90.25 cm2) industrial wafer with a thickness of 155 μm. Series resistance analysis points out probable losses from the hole contact and the base. The limitation of the Transfer Length Method is discussed when used to extract the hole contact resistance. [ABSTRACT FROM AUTHOR]