Intrinsic luminescence-downshifting effects of Zn-based Mn-doped nanoparticle layers on Si solar cells

Abstract

Luminescence downshifting (LDS) effects of Zn-based Mn-doped nanoparticles (NPs) on characteristics of Si solar cells are investigated. ZnSe:Mn/ZnS core-doped core/shell NPs and ZnSe/ZnS:Mn/ZnS shell-doped core/shell/shell NPs are deposited on glass plates using layer-by-layer method. It is found that shell-doped NPs are superior as LDS materials by measuring their optical properties. We deposit LDS layers made of shell-doped NPs on Si cells and measure their internal quantum efficiencies (IQEs) to examine LDS effects separately from the effects of reflection on LDS layers. We find that IQEs for 300-400 nm are more enhanced for cells with thicker LDS layers. IQE at 350 nm is calculated for Si cells with LDS layers coated using an analytical model for the transmittance of downshifted photons into Si cells. IQEs for the respective cells are in qualitative agreement with the measurements.

Intrinsic characteristics of Si solar cells coated with thick luminescence down-shifting sol–gel glass films

“…It was reported that NPs were periodically aligned in LBLbased LDS films. 39) The in-plane and out-of-plane separations between the centers of 5 nm NPs are estimated to be 5 and 5.5 nm, respectively, which means that the number density of NPs in a 140 nm thick LBL-based LDS film, which we previously reported, 28) is 6.0 × 10 18 cm −3 . Given that the IOD of this LDS film was 0.07 at 350 nm, the extinction coefficient at 350 nm was 3.30 × 10 −2 .…”

“…IQE of cells coated with LDS films in the UV wavelength region are be given by the sum of contributions of incident UV photons and downshifted photons emitted from NPs, i.e. IQE of cells coated with LDS films at 350 nm, IQE 350,NP , is expressed as, 28) 28) 140 nm 0.07 3.30 × 10 −2 6.0 × 10 18 cm −3 SK1005-5…”

“…We fabricated n-on-p Si cells by implanting B and P ions on high-resistive p-Si substrates, which were subjected to subsequent annealing. 28) The area of the emitters was 10 mm by 12 mm. Using the same conditions for preparing S1-S3, we formed a sol-gel glass film without NPs, S1′, and two types of NP-dispersed sol-gel glass films, S2′ and S3′, on Si cells.…”

“…We previously deposited Zn-based core-shell NPs on Si cells using the layer-by-layer (LBL) method. 28) The thickness of the deposited films was ∼100 nm. By examining the internal quantum efficiency (IQE) of cells, we directly observed the enhancement of their SR in the UV wavelength region due to the LDS of NPs.…”

“…The measured results were compared with a calculation using a model that we had reported. 28) We also estimated the number density of NPs in the LDS films and discussed relationships between the number density of NPs, optical properties of LDS films, and solar cell characteristics.…”