Biological and bio-inspired mineralization processes yield a variety of three-dimensional structures with relevance for fields such as photonics, electronics and photovoltaics. However, these processes are only compatible with specific material compositions, often carbonate salts, thereby hampering widespread applications. Here we present a strategy to convert a wide range of metal carbonate structures into lead halide perovskite semiconductors with tunable bandgaps, while preserving the 3D shape. First, we introduce lead ions by cation exchange. Second, we use carbonate as a leaving group, facilitating anion exchange with halide, which is followed rapidly by methylammonium insertion to form the perovskite. As proof of principle, pre-programmed carbonate salt shapes such as vases, coral-like forms and helices are transformed into perovskites while preserving the morphology and crystallinity of the initial micro-architectures. This approach also readily converts calcium carbonate biominerals into semiconductors, furnishing biological and programmable synthetic shapes with the performance of artificial compositions such as perovskite-based semiconductors.

Patterning materials with different properties in a single film is a fundamental challenge and essential for the development of next‐generation (opto)electronic functional components. This work introduces the concept of ion exchange lithography and demonstrates spatially controlled patterning of electrically insulating films and semiconductors with tunable optoelectronic properties. In ion exchange lithography, a reactive nanoparticle “canvas” is locally converted by printing ion exchange “inks.” To demonstrate the proof of principle, a canvas of insulating nanoporous lead carbonate is spatioselectively converted into semiconducting lead halide perovskites by contact printing an ion exchange precursor ink of methylammonium and formamidinium halides. By selecting the composition of the ink, the photoluminescence wavelength of the perovskite semiconductors is tunable over the entire visible spectrum. A broad palette of conversion inks can be applied on the reactive film by printing with customizable stamp designs, spray‐painting with stencils, and painting with a brush to inscribe well‐defined patterns with tunable optoelectronic properties in the same canvas. Moreover, the optoelectronic properties of the converted canvas are exploited to fabricate a green light‐emitting diode (LED), demonstrating the functionality potential of ion exchange lithography.

Bottom-up assembly can organize simple building blocks into complex architectures for light manipulation. The optical properties of self-assembled polycrystalline barium carbonate/silica double helices are studied using fluorescent Fourier and Mueller matrix microscopy. Helices doped with fluorescein direct light emission along the long axis of the structure. Furthermore, light transmission measured normal and parallel to the long axis exhibits twist sense-specific circular retardance (CR) and wave-guiding, respectively, albeit the measurements suffer from depolarization. The helices thus integrate highly directional emission with enantiomorphspecific polarization. This optical response emerges from the arrangement of nanoscopic mineral crystallites in the microscopic helix, and demonstrates how bottom-up assembly can achieve ordering across multiple length scales to form complex functional materials.Helical-shaped nanocomposites formed from barium carbonate (BaCO3) nanocrystals and amorphous silica (SiO2) can put these ideas to the test. These bioinspired nanocomposites have been observed to self-assemble into highly intricate, yet controllable, three-dimensional (3D) Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

Shape-preserving conversion offers a promising strategy to transform self-assembled structures into advanced functional components with customizable composition and shape. Specifically, the assembly of barium carbonate nanocrystals and amorphous silica nanocomposites (BaCO 3 /SiO 2 ) offers a plethora of programmable three-dimensional (3D) microscopic geometries, and the nanocrystals can subsequently be converted into functional chemical compositions, while preserving the original 3D geometry. Despite this progress, the scope of these conversion reactions has been limited by the requirement to form carbonate salts. Here, we overcome this limitation using a single-step cation/anion exchange that is driven by the temporal pH change at the converting nanocomposite. We demonstrate the proof of principle by converting BaCO 3 /SiO 2 nanocomposites into tin-containing nanocomposites, a metal without a stable carbonate. We find that BaCO 3 /SiO 2 nanocomposites convert in a single step into hydroromarchite nanocomposites (Sn 3 (OH) 2 O 2 /SiO 2 ) with excellent preservation of the 3D geometry and fine features. We explore the versatility and tunability of these Sn 3 (OH) 2 O 2 /SiO 2 nanocomposites as a precursor for functional compositions by developing shape-preserving conversion routes to two desirable compositions: tin perovskites (CH 3 NH 3 SnX 3 , with X = I or Br) with tunable photoluminescence (PL) and cassiterite (SnO 2 )—a widely used transparent conductor. Ultimately, these findings may enable integration of functional chemical compositions into advanced morphologies for next-generation optoelectronic devices.

Two-dimensional (2D) lead halide perovskites are an exciting class of materials currently being extensively explored for photovoltaics and other optoelectronic applications. Their ionic nature makes them ideal candidates for solution...