| Work Detail |
The tandem device is based on a bottom thin-film heterojunction cell that can bend and a top perovskite cell that can be manufactured with a low-temperature process to prevent damage. It achieved the highest efficiency ever recorded to date for a flexible perovskite-silicon tandem solar cell. Researchers at Tokyo City University have fabricated a bendable tandem solar cell based on a top semi-transparent inverted perovskite cell and a flexible bottom thin-film silicon heterojunction (HJT) PV device. “Stable and flexible silicon heterojunctions can be fabricated by thinning silicon, thereby enabling the production of light-weight and flexible solar cells suitable for various applications such as building-integrated photovoltaics,” the researchs corresponding author, Ryosuke Ishikawa, told pv magazine. For the thinning of the 21.1%-efficient bottom cell, the research group used a technique known as potassium hydroxide (KOH) etching, which is a wet chemical etching process used to create cavities in silicon. It was used to texture the cell wafer on the back side, while the front side was micro-textured and rounded. The scientists also deposited a protective layer made of silicon nitride (SiNx) film on both sides of the wafer by chemical vapor deposition (CVD). The wafer was then cut into 5 cm square pieces, and the SiNx film along the outer edges was removed using a laser. The top cell was fabricated with a self-assembled monolayer made of MeO-2PACz, which is also known as [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid, a glass substrate coated with indium tin oxide (ITO), a perovskite absorber with an energy bandgap of 1.68 eV, an electron transport layer (ETL) made of buckminsterfullerene (C60), a tin oxide (SnO2), another ITO layer, an anti-reflective coating based on magnesium fluoride (MgF2), and a silver (Ag) metal contact. Tested under standard illumination conditions, the tandem cell achieved a power conversion efficiency of 26.5%, an open-circuit voltage of 1.83 V, a short-circuit current density of 17.9 mA/cm2, and a fill factor of 81.%. This result represents the highest efficiency ever recorded for a flexible perovskite-silicon tandem solar cell, according to the research group. Looking forward, the researchers said they intend to enhance the current in the bottom cell with a more precise design of the back-reflection structure. “To further enhance the conversion efficiency, future research should involve improving current matching by applying a bifacial heterojunction to the bottom cell,” they further explain. “We also intend to conduct detailed evaluations of the bending properties and durability of this tandem solar cell.” The novel cell concept was presented in “High-Efficiency Perovskite/Silicon Tandem Solar Cells with Flexibility,” published in Solar RLL. |
