Opportunity
Organic-inorganic hybrid perovskites have shown remarkable promise for optoelectronic devices, particularly perovskite solar cells (PVSCs), due to their excellent properties like high absorption coefficients and long carrier diffusion lengths. While conventional (n-i-p) architecture PVSCs have achieved high power conversion efficiencies (PCEs), the inverted (p-i-n) structure, which offers advantages such as lower-temperature processing and better compatibility with tandem and flexible devices, still suffers from performance limitations. A key challenge hindering further improvement in inverted PVSCs is the significant energy loss, primarily from non-radiative recombination caused by defects at the perovskite film's surface and grain boundaries. The intrinsic quality of the perovskite film—including its morphology, phase stability, and defect density—is critical for achieving high efficiency and long-term stability. Common strategies to enhance film quality involve using additives to control crystallization. However, many effective additives, especially volatile ones like certain solvents and organic salts, tend to evaporate during the annealing process. This evaporation can create voids at critical interfaces, such as between the perovskite and the substrate, leading to increased recombination sites and accelerated device degradation. Therefore, there is a pressing need for a stable additive that remains within the film to continuously passivate defects and improve film quality without causing detrimental voids, thereby unlocking the full potential of inverted perovskite solar cells and facilitating their commercialization.
Technology
This patent addresses the aforementioned challenges by introducing a novel class of multifunctional nonvolatile additives (MNAs) into organic-inorganic hybrid perovskite materials and their precursor solutions. The core innovation lies in the molecular design of these MNAs, which feature both acidic groups (e.g., -COOH, -SO3H, -PO3H2) and basic groups (e.g., guanidinium or ammonium groups) on an aryl or heteroaryl backbone. A representative example is 4-guanidinobenzoic acid hydrochloride (GBAC). When added to the perovskite precursor solution, these MNAs form a hydrogen bond-bridged intermediate phase with the perovskite precursors (like PbI2) and the solvent molecules (e.g., DMF). This intermediate phase, which exhibits a one-dimensional organic-inorganic hybrid chain structure, effectively modulates the crystallization kinetics. It slows down the film formation process, allowing for the growth of perovskite films with larger grain sizes (up to 1 μm), enhanced crystallinity, smoother surfaces, and significantly reduced defect densities at grain boundaries. Crucially, unlike volatile additives, these MNAs are nonvolatile and remain embedded within the final perovskite film after annealing. They continue to function as effective passivators, chemically interacting with and neutralizing defect sites. This dual function—controlling crystallization during film formation and providing persistent defect passivation in the final film—is the key technological advancement. The perovskite composition typically includes cations like formamidinium (FA+), methylammonium (MA+), and cesium (Cs+), with lead (Pb2+) as the common divalent metal, and the MNA is incorporated in a molar ratio (m) typically between 0.01 and 0.5 relative to the perovskite structure.
Advantages
- Achieves high-quality perovskite films with large grain sizes (up to ~1 μm), reduced pinholes, and smoother surfaces.
- Significantly lowers trap density (from 2.64×10^16 cm^-3 to 1.76×10^16 cm^-3) and reduces Urbach energy (from 40 meV to 30 meV), indicating minimized electronic disorder and defects.
- Enables inverted (p-i-n) perovskite solar cells to reach record-high power conversion efficiencies (PCEs) of up to 24.8%, rivaling conventional architectures.
- Provides excellent long-term stability; devices retain over 90% of initial PCE after 500 hours of maximum power point tracking under illumination and show minimal decay after 1200 hours of thermal aging at 65°C.
- The nonvolatile nature of the additive prevents the formation of voids at interfaces that are common with volatile additives, leading to more robust film morphology.
- The strategy demonstrates general applicability, also improving the performance of wider-bandgap perovskites used in tandem solar cells.
Applications
- High-efficiency, stable single-junction perovskite solar cells (PVSCs), particularly in the inverted (p-i-n) device architecture.
- Perovskite-based tandem solar cells, where the perovskite layer serves as the top cell combined with silicon or other bottom cells.
- Flexible and lightweight photovoltaic devices due to the low-temperature process compatibility of the inverted structure.
- Other optoelectronic devices leveraging perovskite materials, such as light-emitting diodes (LEDs), photodetectors, and lasers.
- Large-area perovskite solar modules, as demonstrated by the fabrication of devices with active areas of ~1 cm² maintaining good performance.
