Prof Laura Herz FRS

Abstract:

Obtaining micron-thick perovskite films of high quality is key to realizing efficient and stable positive (p)-intrinsic (i)-negative (n) perovskite solar cells^1,2, but it remains a challenge. Here we report an effective method for producing high-quality, micron-thick formamidinium-based perovskite films by forming coherent grain boundaries, in which high-Miller-index-oriented grains grow on the low-Miller-index-oriented grains in a stabilized atmosphere. The resulting micron-thick perovskite films, with enhanced grain boundaries and grains, showed stable material properties and outstanding optoelectronic performances. The small-area solar cells achieved efficiencies of 26.1%. The 1-cm² devices and 5 cm × 5 cm mini-modules delivered efficiencies of 24.3% and 21.4%, respectively. The devices processed in a stabilized atmosphere presented a high reproducibility across all four seasons. The encapsulated devices exhibited superior long-term stability under both light and thermal stressors in ambient air.

Abstract:

Controlling crystal growth alignment in low-dimensional perovskites (LDPs) for solar cells has been a persistent challenge, especially for low-n LDPs (n < 3, n is the number of octahedral sheets) with wide band gaps (>1.7 eV) impeding charge flow. Here we overcome such transport limits by inducing vertical crystal growth through the addition of chlorine to the precursor solution. In contrast to 3D halide perovskites (APbX3), we find that Cl substitutes I in the equatorial position of the unit cell, inducing a vertical strain in the perovskite octahedra, and is critical for initiating vertical growth. Atomistic modelling demonstrates the thermodynamic stability and miscibility of Cl/I structures indicating the preferential arrangement for Cl-incorporation at I-sites. Vertical alignment persists at the solar cell level, giving rise to a record 9.4% power conversion efficiency with a 1.4 V open circuit voltage, the highest reported for a 2 eV wide band gap device. This study demonstrates an atomic-level understanding of crystal tunability in low-n LDPs and unlocks new device possibilities for smart solar facades and indoor energy generation.

Abstract:

The possibility to combine organic semiconducting materials with inorganic halide perovskites opens exciting pathways toward tuning optoelectronic properties. Exploring stable and nontoxic, double perovskites as a host for electroactive organic cations to form two-dimensional (2D) hybrid materials is an emerging opportunity to create both functional and lead-free materials for optoelectronic applications. By introducing naphthalene and pyrene moieties into Ag-Bi-I and Cu-Bi-I double perovskite lattices, intrinsic electronic challenges of double perovskites are addressed and the electronic anisotropy of 2D perovskites can be modulated. (POE)₄AgBiI₈ containing pyrene moieties in the 2D layers was selected from a total of eight new 2D double perovskites, exhibiting a favorable electronic band structure with a type IIb multiple quantum well system based on a layer architecture suitable for out-of-plane conductivity and leading to a photocurrent response ratio of almost 3 orders of magnitude under AM1.5G illumination. Finally, an exclusively parallelly oriented thin film of (POE)₄AgBiI₈ was integrated into a device to construct the first pure n = 1 Ruddlesden-Popper 2D double perovskite solar cell.