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

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

Research output: Contribution to journalArticle

159 Citations (Scopus)

Abstract

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
Volume113
Issue number1
DOIs
StatePublished - Jan 7 2013
Externally publishedYes

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heterojunctions
solar cells
oxides
silicon
metals
short circuit currents
reflectors
amorphous silicon
evanescent waves
ITO (semiconductors)
open circuit voltage
plasmons
electron mobility
ray tracing
polarized light
simulators
high voltages
electric contacts
penetration
incidence

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Holman, Z., Filipič, M., Descoeudres, A., De Wolf, S., Smole, F., Topič, M., & Ballif, C. (2013). Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells. Journal of Applied Physics, 113(1), [013107]. https://doi.org/10.1063/1.4772975

Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells. / Holman, Zachary; Filipič, Miha; Descoeudres, Antoine; De Wolf, Stefaan; Smole, Franc; Topič, Marko; Ballif, Christophe.

In: Journal of Applied Physics, Vol. 113, No. 1, 013107, 07.01.2013.

Research output: Contribution to journalArticle

Holman, Z, Filipič, M, Descoeudres, A, De Wolf, S, Smole, F, Topič, M & Ballif, C 2013, 'Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells', Journal of Applied Physics, vol. 113, no. 1, 013107. https://doi.org/10.1063/1.4772975
Holman, Zachary ; Filipič, Miha ; Descoeudres, Antoine ; De Wolf, Stefaan ; Smole, Franc ; Topič, Marko ; Ballif, Christophe. / Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells. In: Journal of Applied Physics. 2013 ; Vol. 113, No. 1.
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