Efficient and Stable Perovskite Solar Cell with Safe-to-Use

Presently, over 85% of the world's energy is provided by non-renewable fossil fuels with concealed consequences on health and the environment. Developing and engineering novel materials and devices to provide efficient and sustainable energy is imperative. Metal halide perovskite solar cells (PSCs) have attracted enormous attention from academic and industrial communities due to their great promise of addressing the scalability challenges for affordable clean energy.<br/>Power conversion efficiencies (PCEs) as high as 25.7% have been realized for single-junction conventional (n-i-p) PSCs, comparable to state-of-the-art crystalline-silicon solar cells. Inverted (p-i-n) devices have exhibited greater stability and lifetimes because of their un-doped hole-transporting layers (HTLs) and the formation of highly crystalline perovskite films, while their PCE still lag the conventional devices. Interfacial engineering to mitigate the interface recombination in the heterojunctions between perovskites and charge-transporting layers was considered as one of the promising strategies to further improve the photovoltaic performance and long-term stability of PSCs. Another concern occurs from the toxic element lead (Pb), a significant portion of the active layer in the most efficient PSCs. The potential risk of lead leaking due to damage by natural factors becomes the biggest challenge in entering the market.<br/>To understand the impacts of the interface on perovskite, we systematically study interfacial engineering with respect to molecule design. We have developed a ferrocene-based organometallic interface material (FcTc₂), the functional groups assembled in the side arms of the ferrocene unit can provide chemical solid Pb-O binding between perovskite and molecule, effectively reducing surface trap states. Moreover, the electron-rich and electron-delocalized ferrocene units can accelerate interfacial electron transfer. These synergetic effects of FcTc₂ contribute to a record PCE of inverted PSCs and superior device operational stability, leading to a PCE of 25.0% (with certified 24.3%) and maintaining&gt; 98% of its initial efficiency after continuously operating at the maximum power point for 1500 hours under simulated AM1.5 illumination. It is noteworthy that the FcTc₂-based device exhibited satisfactory durability under damp heat environment, which meet the IEC61215:2016 qualification (<i>Science</i> 2022, 376, 416-420).<br/>For the lead leakage prevention in PSCs, we designed and synthesized novel lead trapping materials. Cation exchange resin (CER) and sulfonated graphene aerogels (S-GA) were first assembled in rigid and flexible perovskite PV encapsulation structures. The extremely low-cost CER with a sulphonic acid group (SO^3-) in Na⁺ form possesses efficient adsorption capability of Pb²⁺. More than 90% of the Pb²⁺ from the degraded perovskite PV solar modules (PSMs) could be captured under simulated severe weather conditions. The lead leaching of perovskite solar modules could meet the requirement of the US Resource Conservation and Recovery Act Regulation (RCRA) (<i>Nano Energy</i> 2022, 93, 106853). The large specific area of sulfonated graphene aerogels and their high binding energy with Pb²⁺ give them superior lead adsorption capacity in an aqueous solution. The encapsulant can capture over 99% of Pb²⁺ from the degraded flexible PSMs under different simulated conditions (scratching, bending, and thermal circling) to reduce the lead leakage to ≈10 ppb (<i>Adv. Energy Mater.</i> 2022, 12, 2103236). We also designed the thiol-functionalized 2D conjugated MOF as an electron extraction layer at the perovskite/cathode interface for electron extraction and Pb leakage prevention (<i>Nat. Nanotech. </i>2020, <i>15</i>, 934). These works pave the way for the real-life application of perovskite photovoltaic technology.