Silvia Martin de Nicolas

Silicon heterojunction solar cell with passivated hole selective MoOx contact

We explore substoichiometric molybdenum trioxide (MoOx, x < 3) as a dopant-free, hole-selective contact for silicon solar cells. Using an intrinsic hydrogenated amorphous silicon passivation layer between the oxide and the silicon absorber, we demonstrate a high open-circuit voltage of 711 mV and power conversion efficiency of 18.8%. Due to the wide band gap of MoOx, we observe a substantial gain in photocurrent of 1.9 mA/cm2 in the ultraviolet and visible part of the solar spectrum, when compared to a p-type amorphous silicon emitter of a traditional silicon heterojunction cell. Our results emphasize the strong potential for oxides as carrier selective heterojunction partners to inorganic semiconductors.

22.5% efficient silicon heterojunction solar cell with molybdenum oxide hole collector

Substituting the doped amorphous silicon films at the front of silicon heterojunction solar cells with wide-bandgap transition metal oxides can mitigate parasitic light absorption losses. This was recently proven by replacing p-type amorphous silicon with molybdenum oxide films. In this article, we evidence that annealing above 130 °C—often needed for the curing of printed metal contacts—detrimentally impacts hole collection of such devices. We circumvent this issue by using electrodeposited copper front metallization and demonstrate a silicon heterojunction solar cell with molybdenum oxide hole collector, featuring a fill factor value higher than 80% and certified energy conversion efficiency of 22.5%.

Organic-Inorganic Halide Perovskites: Perspectives for Silicon-Based Tandem Solar Cells

We investigate the efficiency potential of organic-inorganic halide perovskite/crystalline silicon tandem solar cells, a new class of photovoltaic devices targeting long-term cost reductions by ultrahigh conversion efficiencies. Methyl ammonium lead triiodide perovskite solar cells are particularly interesting as the top cell in Si-based tandem devices due to their suitable band gap, high photovoltage, and low sub-bandgap absorption. We derive optical models for a perovskite/Si tandem cell with Lambertian light trapping in the perovskite top cell, as well as for a top cell in the single pass limit. We find that unlike for other thin-film device architectures, light trapping is not required for the triiodide perovskite/Si tandem to reach matched top and bottom cell currents. While a Lambertian top cell could be employed in a four-terminal tandem, a top cell in the single pass limit enables a current-matched monolithic device with realistic top cell thicknesses. We calculate a limiting efficiency of 35.67% for an ideal (no parasitic absorption, ideal contacts) monolithic tandem, assuming a top cell open-circuit voltage of 1100 mV.

Back-Contacted Silicon Heterojunction Solar Cells With Efficiency >21%

We report on the fabrication of back-contacted silicon heterojunction solar cells with conversion efficiencies above 21%. Our process technology relies solely on simple and size-scalable patterning methods, with no high-temperature steps. Using in situ shadow masks, doped hydrogenated amorphous silicon layers are patterned into two interdigitated combs. Transparent conductive oxide and metal layers, forming the back electrodes, are patterned by hot melt inkjet printing. With this process, we obtain high short-circuit current densities close to 40 mA/cm2 and open-circuit voltages exceeding 720 mV, leading to a conversion efficiency of 21.5%. However, moderate fill factor values limit our current device efficiencies. Unhindered carrier transport through both heterocontact layer stacks, as well as higher passivation quality over the minority carrier-injection range relevant for solar cell operation, are identified as key factors for improved fill factor values and device performance.

Photolithography-free interdigitated back-contacted silicon heterojunction solar cells with efficiency >21%

We report on the development of interdigitated back-contacted silicon heterojunction solar cells with conversion efficiencies well above 21%. Doped hydrogenated amorphous silicon layers, needed for electron and hole collection, are patterned via in-situ shadow masking whereas transparent conductive oxide and metal layers, of the back electrodes, are defined via hot melt inkjet printing of an etch resist and subsequent wet etching. Our technology is therefore photolithography-free and avoids any high-temperature step. The best fabricated solar cell presents a high short-circuit current density of 39.9 mA/cm2, an open-circuit voltage of 724 mV and a fill factor of 74.5% resulting in a conversion efficiency of 21.5%, with a strong upside potential. We report also on a silver-free IBC-SHJ solar cell with conversion efficiency >20%.

Hole selective MoO x contact for silicon heterojunction solar cells

Efficient carrier selective contacts and excellent surface passivation are essential for solar cells to reach high power conversion efficiencies. Exploring MoOx as a dopant-free, hole-selective contact in combination with an intrinsic hydrogenated amorphous silicon passivation layer between the oxide and the crystalline silicon absorber, we demonstrate a silicon hetero-junction solar cell with a high open-circuit voltage of 711 mV and a power conversion efficiency of 18.8%. Compared to the traditional p-type hydrogenated amorphous silicon emitter of a traditional silicon heterojunction solar cell, we observe a substantial gain in photocurrent of 1.9 mA/cm2 for MoOx due to its wide band gap of 3.3 eV. Our results on MoOx have important implications for other combinations of transition metal oxides and photovoltaic absorber materials.

Transparent electrodes in silicon heterojunction solar cells: Influence on carrier recombination

Hole and electron collectors in silicon heterojunction solar cells consist of hydrogenated amorphous silicon layer stacks deposited on the crystalline silicon wafer surfaces. Charge carrier extraction from these layers is achieved by electrodes consisting of a transparent conductive oxide and a metal layer. Earlier, the mere presence of the transparent conductive oxide layer on top of the hole collecting stack was shown to alter minority carrier lifetimes, at low minority injection levels, of the crystalline silicon absorber. In this work, we present a detailed investigation of the magnitude and nature of these effects and discuss their impact on silicon heterojunction solar cell performance for the different device architectures.