Maximizing the power conversion efficiency (PCE) of perovskite/silicon tandem solar cells that can exceed the Shockley-Queisser single-cell limit requires a high-performing, stable perovskite top cell with a wide bandgap. We developed a stable perovskite solar cell with a bandgap of ~1.7 electron volts that retained more than 80% of its initial PCE of 20.7% after 1000 hours of continuous illumination. Anion engineering of phenethylammonium-based two-dimensional (2D) additives was critical for controlling the structural and electrical properties of the 2D passivation layers based on a lead iodide framework. The high PCE of 26.7% of a monolithic two-terminal wide-bandgap perovskite/silicon tandem solar cell was made possible by the ideal combination of spectral responses of the top and bottom cells.

Z-scheme in natural photosynthesis are promising for solar-driven CO 2 conversion. [2] By combining multiple photoelectrodes or photovoltaics (PV), the Z-scheme PEC cells can provide sufficient photopotential to simultaneously drive water oxidation and CO 2 reduction under minimal or no external bias. [3] Nevertheless, lowering the kinetic barrier of thermodynamically inert CO 2 remains a hurdle for efficient CO 2 reduction. The development of CO 2reducing biocatalyst-conjugated cathodes can improve chemoselectivity and increase yield under mild conditions. [4] Compared to synthetic catalysts that often require extreme conditions such as high pressure, pH, or temperature, enzymes show high catalytic activities and specificities under mild conditions, making them a valuable catalyst for sustainable and green applications. In particular, formate dehydrogenase (FDH) is an attractive redox enzyme that reduces CO 2 to formate, an alternative water-soluble feedstock that can be easily converted to other common fuels. [5] Previous studies have focused on mediated electron transfer (MET)-type reactions, [6] in which redox mediators such as nicotinamide adenine dinucleotide cofactor (NADH) and Rh-based complexes shuttle electrons between an electrode and FDH. However, the MET-based biocatalysis requires costly electron mediators and multiple electron transfer steps that cause side reactions and significant losses in efficiency. [7] Here, we report the development of 3D titanium nitride nanoshell (3D TiN) electrodes for biocatalytic PEC cells that convert CO 2 to formate through direct electron transfer (DET), as depicted in Scheme 1a. A highly ordered, porous TiN structure is employed as an electrically conductive scaffold for efficient DET to a W-containing FDH from Clostridium ljungdahlii (ClFDH) (inset, Scheme 1a). TiN was chosen as a scaffold for DET-based bioelectrode because it is highly conductive, electrochemically stable and exhibit high chemical and thermal resistance, as well as exceptional hardness. [8] The 3D TiN electrode simultaneously provides (i) a large electroactive surface area generated from an ultrathin (≈30 nm), 3D nanoshell structure with high porosity (92.1%) for high enzyme loading per geometric area, (ii) a continuous electron transfer network with high electrical Z-scheme-inspired tandem photoelectrochemical (PEC) cells have received attention as a sustainable platform for solar-driven CO 2 reduction. Here, continuously 3D-structured, electrically conductive titanium nitride nanoshells (3D TiN) for biocatalytic CO 2 -to-formate conversion in a bias-free tandem PEC system are reported. The 3D TiN exhibits a periodically porous network with high porosity (92.1%) and conductivity (6.72 × 10 4 S m −1 ), which allows for high enzyme loading and direct electron transfer (DET) to the immobilized enzyme. It is found that the W-containing formate dehydrogenase from Clostridium ljungdahlii (ClFDH) on the 3D TiN nanoshell is electrically activated through DET for CO 2 reduction. At a low overpotential...

Redox enzymes catalyze fascinating chemical reactions with excellent regio- and stereo-specificity. Nicotinamide adenine dinucleotide cofactor is essential in numerous redox biocatalytic reactions and needs to be regenerated because it is consumed as an equivalent during the enzymatic turnover. Here we report on unbiased photoelectrochemical tandem assembly of a photoanode (FeOOH/BiVO4) and a perovskite photovoltaic to provide sufficient potential for cofactor-dependent biocatalytic reactions. We obtain a high faradaic efficiency of 96.2% and an initial conversion rate of 2.4 mM h−1 without an external applied bias for the photoelectrochemical enzymatic conversion of α-ketoglutarate to l-glutamate via l-glutamate dehydrogenase. In addition, we achieve a total turnover number and a turnover frequency of the enzyme of 108,800 and 6200 h−1, respectively, demonstrating that the tandem configuration facilitates redox biocatalysis using light as the only energy source.

The solution process is the most widely used method to prepare perovskite absorbers for high performance solar cells due to its ease for fabrication and low capital cost.