The origin of reduced fill factors of emitter‐wrap‐through‐solar cells

Self Cite

Modeling of transport and recombination of charge carriers in solar cells is useful for understanding and improving the device performance. We implement the fully coupled transport equations for electrons and holes into the finite‐element partial differential equation solver COMSOL. The dopant‐diffused surface regions such as junctions, floating junctions, or back surface field layers are treated as conductive boundaries of the volume in which the semiconductor equations are solved. This so‐called conductive boundary (CoBo) model characterizes diffused layers by their sheet resistances and diode saturation current densities. Both are directly experimentally accessible. The CoBo model exhibits excellent numerical stability and enables two‐dimensional simulations on a laptop. We find agreement when testing the two‐dimensional COMSOL implementation of the CoBo model for one‐dimensional devices against simulations using the code PC1D. We apply the CoBo model to elucidate how the sheet resistance of diffused vias impacts the power conversion efficiency of emitter wrap through solar cells. Copyright © 2010 John Wiley & Sons, Ltd.

Section: Varying the Resistance R V Via Holes: Simulation S2supporting

confidence: 90%

Modeling solar cells with the dopant‐diffused layers treated as conductive boundaries

Brendel

2011

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“…The V oc of the cells is below values reported for EWT‐cells on high quality material 42, 43. For high quality material the V oc loss due to double sided minority carrier collection is expected to be negligible.…”

Section: Cell Resultscontrasting

confidence: 57%

Screen‐printed Emitter‐Wrap‐Through solar cell with single step side selective emitter with 18.8% efficiency

Mingirulli

Stüwe

Specht

et al. 2011

A fabrication process for Emitter‐Wrap‐Through solar cells on monocrystalline material with high quality gap passivation by wet thermal silicon dioxide is investigated. Masking and structuring steps are performed by screen‐printing technology. Via‐holes are created by an industrially applicable high‐speed laser drilling process. The cell structure features a selective emitter structure fabricated in a single high temperature step: a highly doped emitter at the via‐holes and the rear side, allowing for a low via‐hole resistivity as well as a low resistivity contact to screen‐printed pastes, and a moderately doped front side emitter exhibiting high quantum efficiency in the low wavelength range. Therefore a novel approach is applied depositing either doped or undoped PECVD silicon dioxide layers on the front side. It is shown that doping profiles advantageous for the EWT‐cell structure can be achieved. The screen‐printed aluminum paste is found to penetrate the underlying thermal dioxide layer at appropriate contact firing conditions leading to a zone of high recombination in the overlap region of aluminum and silicon dioxide. It is shown that conventional PECVD‐anti‐reflection silicon nitride acts as effective protection layer reducing the recombination in this region. Designated area conversion efficiencies up to 18.8% on FZ material are obtained applying the single step side selective emitter fabrication technique. Copyright © 2010 John Wiley & Sons, Ltd.

“…Despite a very different solar cell concept, this fill factor effect of the back-junction BESC is reminiscent of effects observable for emitter-wrap-through solar cells. 15,16 It is further noted that despite the absence of any junction shunting the shape of the I-V curves in Figure 9 nevertheless do suggest the presence of junction shunting for small and intermediate resistance values of R 1 (e.g. 20 Vcm 2 ) and may lead to an erroneous assessments of the loss mechanisms in experimentally prepared devices.…”

Section: Discussion Of the Fill Factormentioning

confidence: 97%

Numerical simulations of buried emitter back‐junction solar cells

Harder

Mertens

Brendel

2009

Self Cite

We recently introduced the buried emitter back-junction solar cell, featuring large area fractions of overlap between n R -type and p R -type regions at the rear side of the device. In this paper we analyse the performance of the buried emitter solar cell (BESC) and its generalisations by one-dimensional device simulations and analytical model calculations. A key finding is that the generalised versions of the BESC structure allows achieving very high efficiencies by passivating virtually the entire surface of p-type emitters by an oxidised n-type surface layer. A disadvantage of this type of full-area emitter passivation in the generalised backjunction BESC is the need for an insulating layer between the metallisation of the emitter and the contact to the base, which is technologically difficult to achieve.