Excitonic metal oxide heterojunction (NiO/ZnO) solar cells for all-transparent module integration

•All metal oxide device is proposed for advanced transparent solar cells and modules.•Ultraviolet active ZnO/NiO junction demonstrated power conversion efficiency of 6%.•All transparent metal oxide (ZnO/NiO) device is fabricated room temperature.•Room temperature excitons in the crystalline ZnO are described.

Could transparent solar cells work as the invisible power generator? Is it possible, in order to satisfy the on-site energy production, to install the transparent solar cell into the window of buildings and vehicles without recognizing the existence of energy harvesting entities?Here we propose and demonstrate the wide energy bandgap materials for visible light transmittance and UV photon absorption for power generation. All-transparent solar cell was achieved by the heterojunction of metal oxide layers. By using the solid-state sputtering method, transparent heterojunction (p-type NiO/n-type ZnO) was realized. A unit cell gave the record-high conversion efficiency of 6% with the enormous current density (2.7 mA/cm2) and open circuit voltage of 532 mV. The remarkable transparent solar power is mainly attributed to the absolute UV absorption to induce the substantial excitonic effect for ZnO/NiO heterojunction.For integration, the transparent solar cell units were fabricated on a glass substrate to demonstrate the module of unit solar cells. Using the 3 × 3 unit cell solar module, a significant output voltage (> 2 V) was achieved to confirm the excellent connection manipulation of transparent solar cell units. By putting the transparent solar cells on buildings and vehicles, the electric power is spontaneously supplied from the Sun power but human eyes have no visible scarification. Transparent solar cells would provide a route for on-site energy generation.

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