Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells

Zachary C. Holman*, Miha Filipič, Antoine Descoeudres, Stefaan De Wolf, Franc Smole, Marko Topič, Christophe Ballif

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

252 Scopus citations


Silicon heterojunction solar cells have record-high open-circuit voltages but suffer from reduced short-circuit currents due in large part to parasitic absorption in the amorphous silicon, transparent conductive oxide (TCO), and metal layers. We previously identified and quantified visible and ultraviolet parasitic absorption in heterojunctions; here, we extend the analysis to infrared light in heterojunction solar cells with efficiencies exceeding 20%. An extensive experimental investigation of the TCO layers indicates that the rear layer serves as a crucial electrical contact between amorphous silicon and the metal reflector. If very transparent and at least 150 nm thick, the rear TCO layer also maximizes infrared response. An optical model that combines a ray-tracing algorithm and a thin-film simulator reveals why: parallel-polarized light arriving at the rear surface at oblique incidence excites surface plasmons in the metal reflector, and this parasitic absorption in the metal can exceed the absorption in the TCO layer itself. Thick TCO layers - or dielectric layers, in rear-passivated diffused-junction silicon solar cells - reduce the penetration of the evanescent waves to the metal, thereby increasing internal reflectance at the rear surface. With an optimized rear TCO layer, the front TCO dominates the infrared losses in heterojunction solar cells. As its thickness and carrier density are constrained by anti-reflection and lateral conduction requirements, the front TCO can be improved only by increasing its electron mobility. Cell results attest to the power of TCO optimization: With a high-mobility front TCO and a 150-nm-thick, highly transparent rear ITO layer, we recently reported a 4-cm2 silicon heterojunction solar cell with an active-area short-circuit current density of nearly 39 mA/cm2 and a certified efficiency of over 22%.

Original languageEnglish (US)
Article number013107
JournalJournal of Applied Physics
Issue number1
StatePublished - Jan 7 2013

Bibliographical note

Funding Information:
We thank Darrell Schroeter, Franz-Josef Haug, Benjamin Lipovšek, and Janez Krč for insightful discussions, and Andrej Čampa for AFM measurements. This work was supported by the European Union Seventh Framework Programme (FP7/2007-2013), Collaborative Project (CP) ‘20plμs' with the full title: ‘Further development of very thin wafer based c-Si photovoltaics' under Grant Agreement No. 256695, by Axpo Naturstrom Fonds, Switzerland, and by the Swiss Commission for Technology and Innovation. M.F. thanks the Slovenian Research Agency (P2-0197) for providing PhD funding and The Slovene Human Resources and Scholarship Fund for funding a 6-month research visit to the EPFL PV-Lab.

ASJC Scopus subject areas

  • Physics and Astronomy(all)


Dive into the research topics of 'Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells'. Together they form a unique fingerprint.

Cite this