A new metal transfer process for van der Waals contacts to vertical Schottky-junction transition metal dichalcogenide photovoltaics

Two-dimensional transition metal dichalcogenides are promising candidates for ultrathin optoelectronic devices due to their high absorption coefficients and intrinsically passivated surfaces. To maintain these near-perfect surfaces, recent research has focused on fabricating contacts that limit Fermi-level pinning at the metal-semiconductor interface. Here, we develop a new, simple procedure for transferring metal contacts that does not require aligned lithography. Using this technique, we fabricate vertical Schottky-junction WS₂ solar cells, with Ag and Au as asymmetric work function contacts. Under laser illumination, we observe rectifying behavior and open-circuit voltage above 500 mV in devices with transferred contacts, in contrast to resistive behavior and open-circuit voltage below 15 mV in devices with evaporated contacts. One-sun measurements and device simulation results indicate that this metal transfer process could enable high specific power vertical Schottky-junction transition metal dichalcogenide photovoltaics, and we anticipate that this technique will lead to advances for two-dimensional devices more broadly

A new metal transfer process for van der Waals contacts to vertical Schottky-junction transition metal dichalcogenide photovoltaics

Two-dimensional transition metal dichalcogenides are promising candidates for ultrathin optoelectronic devices due to their high absorption coefficients and intrinsically passivated surfaces. To maintain these near-perfect surfaces, recent research has focused on fabricating contacts that limit Fermi-level pinning at the metal-semiconductor interface. Here, we develop a new, simple procedure for transferring metal contacts that does not require aligned lithography. Using this technique, we fabricate vertical Schottky-junction WS₂ solar cells, with Ag and Au as asymmetric work function contacts. Under laser illumination, we observe rectifying behavior and open-circuit voltage above 500 mV in devices with transferred contacts, in contrast to resistive behavior and open-circuit voltage below 15 mV in devices with evaporated contacts. One-sun measurements and device simulation results indicate that this metal transfer process could enable high specific power vertical Schottky-junction transition metal dichalcogenide photovoltaics, and we anticipate that this technique will lead to advances for two-dimensional devices more broadly

Non-Epitaxial GaAs Heterojunction Nanowire Solar Cells (PVSC)

The efficiency of substrate-removed GaAs nanowire solar cells can be increased to over 32% by borrowing processes and materials from GaAs MOSFETs and perovskite photovoltaics. Photogenerated carriers fundamentally limit the performance of off-wafer homojunction devices to less than 15% efficiency by creating low resistance pathways for minority carriers to recombine at ohmic contacts. We report the results of coupled optoelectronic device physics simulations of GaAs nanowire homojunction solar cells and GaAs nanocone heterojunction solar cells where SnO₂ and CuSCN are used for charge carrier collection. Our simulations include realistic recombination models for bulk and surface recombination. We find the optimal design is a radial junction with moderately p-type GaAs. Densities of states previously demonstrated in GaAs MOSFETs enable efficiencies greater than 30%

Non-Epitaxial GaAs Heterojunction Nanowire Solar Cells (PVSC)

The efficiency of substrate-removed GaAs nanowire solar cells can be increased to over 32% by borrowing processes and materials from GaAs MOSFETs and perovskite photovoltaics. Photogenerated carriers fundamentally limit the performance of off-wafer homojunction devices to less than 15% efficiency by creating low resistance pathways for minority carriers to recombine at ohmic contacts. We report the results of coupled optoelectronic device physics simulations of GaAs nanowire homojunction solar cells and GaAs nanocone heterojunction solar cells where SnO₂ and CuSCN are used for charge carrier collection. Our simulations include realistic recombination models for bulk and surface recombination. We find the optimal design is a radial junction with moderately p-type GaAs. Densities of states previously demonstrated in GaAs MOSFETs enable efficiencies greater than 30%

Silicon heterojunction solar cells with effectively transparent front contacts

We demonstrate silicon heterojunction solar cells with microscale effectively transparent front contacts (ETCs) that redirect incoming light to the active area of the solar cell. Replacing standard contact electrodes by ETCs leads to an enhancement in short circuit current density of 2.2 mA cm^(−2) through mitigation of 6% shading losses and improved antireflection layers. ETCs enable low loss lateral carrier transport, with cells achieving an 80.7% fill factor. Furthermore, dense spacing of the contact lines allows for a reduced indium tin oxide thickness and use of non-conductive, optically optimized antireflection coatings such as silicon nitride. We investigated the performance of ETCs under varying light incidence angles, and for angles parallel to the ETC lines find that there is no difference in photocurrent density with respect to bare indium tin oxide layers. For angles perpendicular to the ETC lines, we find that the external quantum efficiency (EQE) always outperforms cells with flat contact grids

Integrated Solar-Driven Device with a Front Surface Semitransparent Catalysts for Unassisted CO2 Reduction

Monolithic integrated photovoltaic-driven electrochemical (PV-EC) artificial photosynthesis is reported for unassisted CO2 reduction. The PV-EC structures employ triple junction photoelectrodes with a front mounted semitransparent catalyst layer as a photocathode. The catalyst layer is comprised of an array of microscale triangular metallic prisms that redirect incoming light toward open areas of the photoelectrode to reduce shadow losses. Full wave electromagnetic simulations of the prism array (PA) structure guide optimization of geometries and length scales. An integrated device is constructed with Ag catalyst prisms covering 35% of the surface area. The experimental device has close to 80% of the transmittance with a catalytic surface area equivalent 144% of the glass substrate area. Experimentally this photocathode demonstrates a direct solar-to-CO conversion efficiency of 5.9% with 50 h stability. Selective electrodeposition of Cu catalysts onto the surface of the Ag triangular prisms allows CO2 conversion to higher value products enabling demonstration of a solar-to-C2+ product efficiency of 3.1%. This design featuring structures that have a semitransparent catalyst layer on a PV-EC cell is a general solution to light loss by shadowing for front surface mounted metal catalysts, and opens a route for the development of artificial photosynthesis based on this scalable design approach