Monolithic Si nanocrystal/crystalline Si tandem cells involving Si nanocrystals in SiC

Abstract

Monolithic tandem cells involving a top cell with Si nanocrystals embedded in SiC (Si NC/SiC) and a c-Si bottom cell have been prepared. Scanning electron microscopy shows that the intended cell architecture is achieved and that it survives the 1100 °C anneal required to form Si NCs. The cells exhibit mean open-circuit voltages Voc of 900–950 mV, demonstrating tandem cell functionality, with ≤580 mV arising from the c-Si bottom cell and ≥320 mV arising from the Si NC/SiC top cell. The cells are successfully connected using a SiC/Si tunnelling recombination junction that results in very little voltage loss. The short-circuit current densities jsc are, at 0.8–0.9 mAcm−2, rather low and found to be limited by current collection in the top cell. However, equivalent circuit simulations demonstrate that in current-mismatched tandem cells such as the ones studied here, higher jsc, when accompanied by decreased Voc, can arise from shunts or breakdown in the limiting cell rather than improved current collection from the limiting cell. This indicates that Voc is a better optimisation parameter than jsc for tandem cells where the limiting cell exhibits poor junction characteristics. The high-temperature-stable cell architecture developed in this work, coupled with simulations highlighting potential pitfalls in tandem cell analysis, provides a suitable route for optimisation of Si NC layers for photovoltaics on a tandem cell device level

Monolithic thin-film chalcogenide–silicon tandem solar cells enabled by a diffusion barrier

“…To explore these issues, we compare the results of our tandem device to a baseline single-junction CZTS cell where the CZTS thickness was reduced from the typical 1 µm to a value of around 275 nm, similar to the value used for the tandem. This "thin CZTS cell" achieved an efficiency of 5.8%, with a J sc of 15.8 mA/cm 2 and a V oc of 585 mV (the J-V curve is shown in the supplementary Figure S11), which is fairly comparable to state of the art thin CZTS devices (with a record of 8.57% for a 400 nm thick CZTS [76]). However, when compared to the CZTS growth for the tandem cell, significant morphological differences between the two CZTS layers are noticeable.…”

Strong Absorption Enhancement in Si Nanorods

“…At the limit of the smallest nanostructures, where the size approaches the exciton Bohr radius (∼5 nm), quantum confinement sets in, changing the basic material properties, such as bandgap and k-space structure . This effect can push the efficiency limit higher by allowing a multijunction concept to be realized in the same material. , It can also provide new functionality for this ubiquitous material in photovoltaics and beyond, where ordered 3D arrays of such nanoparticles can form new energy bands suitable for the direct readout . Nanocrystals of silicon can also be used complementarily in solar cells for photon energy downshifting, or photon multiplication by generating more low-energy photons than incoming high-energy quanta .…”

First down converter multilayers integration in an industrial Si solar cell process

“…For example, an increase of 1°C above 25°C leads to a decrease of the SC efficiency by around 0.65% [3][4][5] and results in its faster aging. Several ways to improve the SC efficiency 6 are thus investigated such as tandem cells, 7,8 surface texturing, 9,10 antireflective layer, [11][12][13] or frequency conversion layer. 2,[14][15][16][17][18][19][20] In that respect, down conversion (DC) answers the thermalization issue by converting high energy photons to a greater number of lower energy photons with energies close to the Si-SC gap.…”