Contents of data set for Chemical Control of the Octahedral Network of Solar Absorbers from the CuI-AgI-BiI3 Phase Space via the Discovery of 3D CuAgBiI5 All files are ACSII format as either .txt, .dat, .xy, or .csv Synchrotron XRD and neutron diffraction data (Figure 5) CuAgBiI5 Neutron Powder Diffcation HRPD ISIS CuAgBiI5 Powder X-ray Diffraction I11 Diamond Synchrotron Optical properties - Photoluminescence, UVvis spectroscopy, Time-resolved Photoluminescence, X-ray photoelectonc Spectroscopy (Figure 7) a CuAgBiI5 film UV-Vis and PL b CuAgBiI5 and Cu2AgBiI6 powder XPS c CuAgBiI5 film PL in air d CuAgBiI5 film TRPL Supplmenetary data S2 CuAg1p5Bi0p5I4 PXRD S3 Cu1p5Ag0p5BiI5 PXRD S4 AgBiI4 to CuBiI4 PXRD S7 CuAgBiI5 x=0.16, 0.18 TEM EDX S8 Cu2AgBiI6 x=0.27, 0.29, 0.31, 0.33 TEM EDX S9 CuBiI4 PXRD S13 a TEM EDX CuAgBiI5 0.25g batches b,c PXRD CuAgBiI5 powder 0p25g batches S14 SEM EDX CuAgBiI5 crystal S15 CuAgBiI5 XPS core levels S16 Stability PXRD CuAgBiI5 and Cu2AgBiI6 S17 Raman spectroscopy PXRD CuAgBiI5 and Cu2AgBiI6 S18 a CuAgBiI5 film XRD b CuAgBiI5 film SEM EDX S20 PL Lightsoaking 20mins PL Lightsoaking 90mins S21 a TRPL Vacuum b TRPL Air c TRES Heatmap d TRES spectra e TRES Decays Methods Sample Preparations Optimised CuAgBiI5 Powder Synthesis CuI (0.0318g, 99.999% Sigma–Aldrich) AgI (0.0653g, 99.999% Alfa Aesar) and BiI3 (0.1530g, synthesised as previously reported) powders (nominal composition Cu0.68Ag1.14Bi1.06I5.00, just off the Cu4x(AgBi)1-xI4 solid solution line) were ground together in a pestle and mortar and pressed in to a pellet with a 5 mm diameter. The pellet was sealed in a fused silica tube. The fused silica tubes had a 6 mm internal diameter, 1 mm thick walls and were sealed at 10-4 mbar to 15 cm in length. The sample in the tube was cooled in liquid N2 during the evacuation and sealing process to avoid sublimation of the iodides. The tube was placed upright in a furnace and heated at 5°C/min to 350°C and kept there for 5 days. The tube was taken out after 5 days and the bottom half of it (containing the pellet) was quenched to room temperature in a water bath. The tube was scored and carefully broken open to retrieve the pellet which was then ground in to a black powder. Direct scale up of the CuAgBiI5 powder synthesis from 0.25g to 2.5g led to a small decrease in compositional homogeneity. Therefore, to produce large samples for neutron powder diffraction (NPD) experiments, 0.25g batches of CuAgBiI5 were synthesised and screened for their lattice parameter, purity by PXRD, and average TEM EDX composition and then combined (Figure S4). CuAgBiI5 Crystals A small crystal approx. 20 µm × 15 µm × 10 µm, with an average SEM EDX composition of Cu0.77(1)Ag1.27(3)Bi1.10(5)I5.00(4), was picked out of the CuAgBiI5 powder sample for structural studies via SCXRD (Figure S14). CuAgBiI5 Film Deposition 156.5 mg AgI and 393.1 mg BiI3 were dissolved in 0.8 ml DMSO at 100°C over 15 minutes with constant stirring. In a separate vial, 127 mg of CuI powder were dissolved in 0.5 ml pyridine at 100°C over 15 minutes with constant stirring. The AgBiI in DMSO and CuI in pyridine solutions were quickly filtered through a 0.22 µm pore-size, 13 mm diameter PTFE filter and combined into a single vial. The solutions were kept stirring at 100°C during deposition. Glass substrates were cut to size (approx. 24mm x 24 mm) and sonicated in soap and DI water, acetone and IPA for 15 minutes, dried using an N2 gun, then further cleaned in a U.V.-Ozone generator. After which, the substrates were quickly transferred to a dry box and heated to 150°C for deposition. 100 ul of the hot CuAgBiI solution was deposited dynamically on to the hot substrate and spun at 4000 rpm for 45 seconds on a spincoater. The films were then annealed at 50°C for 30 minutes in air, over which the films turned from a clear orange film to a dark red-brown film. The film was then annealed at 150°C for 15 seconds in air to form the dark black film. Films were transferred to and kept in a N2 filled glovebox until used for measurements. Characterisation Methods Powder X-ray diffraction (PXRD) Initial compositional screening and solution processing experiments made use of PXRD data measured on a Panalytical X’Pert Pro diffractometer using Co Ka1 radiation (? = 1.7890 Å) in Bragg–Brentano geometry and an X’Celerator detector. Phase identification was carried out using the X’Pert HighScore Plus (Version 2.2a) with the PDF-2-ICDD database. PXRD data of capillaries used for photostability assessment were measured on a Bruker D8 Advance diffractometer using monochromated Mo Ka1 radiation (? = 0.7093 Å). PXRD patterns used for detailed structural analysis were collected at room temperature using the MAC detectors on the I11 beamline at Diamond Light Source (RAL, Oxfordshire, U.K.) with a wavelength of ? = 0.825898 Å. Samples were mixed with 50 vol% amorphous boron to reduce absorption effects and contained within 0.3 mm diameter borosilicate capillaries. TopasAcademic (Version 5) was used to perform Pawley fittings and Rietveld refinements of the data. VESTA3 was used for graphical representation of the structures. X-ray diffraction patterns collected on CuAgBiI5 films were measured using a Panalytical X’Pert powder diffractometer, using radiation from a Cu-Ka1 source, across 2?? values ranging from 5-40o. Neutron powder diffraction High-resolution time-of-flight (ToF) data were collected on the HRPD instrument at ISIS Neutron and Muon Source (RAL, Oxfordshire, U.K.) of powder samples at room temperature packed in to vanadium cans with a 6 mm diameter. Data from bank 1 and bank 2 were used for Rietveld refinement in combination with the PXRD I11 dataset. Single crystal X-ray diffraction (SCXRD) Data were collected at 100K on a Rigaku MicroMax-007 HF diffractometer with a molybdenum rotating anode microfocus source and a Saturn 724+ detector using Rigaku Crystal Clear v2.0. Unit-cell indexation, data integration, and reduction were performed using Rigaku CrysAlisPro v171.38.43. The structure was partially solved using SHELX-2013, implemented through Olex2. Compositional Analysis Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) was used to measure the composition as a direct elemental analysis technique. Measurements were carried out using a Hitachi S-4800 SEM with an Oxford Instruments model 7200 EDS X-ray detector. Quantification was carried out using the microanalysis suite of the Inca Suite software (Version 4.15). All powders and crystals were sputtered with 15 nm Au to limit charging effects. Transmission Electron Microscopy (TEM) EDX was carried out using an JEOL JEM 2000FXII TEM microscope operating a W electron source operated at 200 kV, using an EDAX EDX detector, with quantification carried out using EDAX Genesis Spectrum (Version 5.217, 21-Jan-2008). All samples were prepared by spreading a finely ground powder onto carbon coated Au grids. Beam intensity had to be lowered, by increasing the spot size of the beam, as to not decompose the samples. All compositions calculated from EDX measurements were normalised to the nominal iodide content unless otherwise stated. Photostability Experiment For the experiments, a Solar Light Model 16S-300-002 Solar Simulator was used which has a spectral output that complies with air mass 1.5 (AM1.5) per the ASTM standard definition. The combination of neutral density filters and lamp-to-sample distance allowed for the tuning of the intensity of the incident light to 1000 W m-2 as measured by a Solar Light Pyranometer PMA2144 and datalogging radiometer PMA2100. Sample temperatures were monitored using a T-type thermocouple and were found to stay below 35°C. For measurements in sealed atmospheres, powder was loaded into thin-walled (0.01 mm wall thickness) borosilicate capillaries under ambient air, dry synthetic air, and helium, and these were sealed with a gas-oxygen torch. The capillaries were then placed in the solar simulator and subjected to the full solar spectrum at an intensity of1000 W m-2. Raman Spectroscopy The measurements were carried out on a Renishaw inVia Reflex with a Leica microscope utilising a 633 nm wavelength red laser with a maximum power of 6.5 mW. The powder samples were measured in borosilicate capillaires and were exposed to 0.5% of the maximum laser power to avoid decomposition of the sample. The spot size was 5 µm. X-ray Photoelectron Spectroscopy (XPS) Measurements were conducted on powders using a SPECS monochromatic Al Ka (1486.6 eV) X-ray source and a PSPMCD5 analyser calibrated to the Ag 3d5/2 peak. For sample work function measurements, a 20V bias was applied to the sample to shift the work function from the analyser work function. Samples were measured at a base pressure of 10-10 mbar. Charge neutralisation at the surface was achieved by means of a low energy electron flood gun and subsequent correction of the binding energy scale to the adventitious C 1s peak (284.8 eV). Fourier-Transform Infrared Spectroscopy (FTIR) Absorption spectra were taken using a Bruker Vertex 80v Fourier-Transform Infrared (FTIR) spectrometer, with a tungsten halogen source and a silicon diode detector. Measurements were carried out under low vacuum (< 5 mbar). To calculate the absorption coefficient, film thickness was measured using a Veeco Dektak 150 profilometer, which gave a thickness of 320±30 nm. Absorption coefficients were calculated as: a= -1/d ln?(T/(1-R)), where d is the sample thickness, T=t_sample/t_ref and R=r_sample/r_ref , and a blank quartz substrate and silver mirror were used as references for the transmission and reflection, respectively. Steady-State Photoluminescence Measurements Photoluminescence (PL) spectra were measured following excitation by a 398 nm continuous wave laser (PicoHarp, LDH-D-C-405M) at a power density of 40.5 Wcm-2. The emitted PL was collected and coupled into a grating spectrometer (Princeton Instruments SP-2558), after which light was detected by an iCCD camera (PI-MAX4, Princeton Instruments). Measurements on three fresh films were carried out under vacuum (<5×10^(-2) mbar). Subsequently, two fresh films were exposed to air over 90 minutes, and short (15 s) measurements were carried out after 20, 60 and 90 minutes at a power density of 39.0 Wcm-2. The measurements involved five acquisitions being taken, every 3 s, under constant illumination over 15 s. Time-Resolved Photoluminescence Measurements Time-Correlated Single Photon Counting was carried out using the same laser as above to photoexcite the thin films, but in pulsed excitation mode with a repetition rate of 5 MHz at fluences of 1480, 410, 180, 50 nJcm-2. Photoluminescence was collected using the same monochromator, with a photon-counting detector (PDM series from MPD). Timing is controlled electronically using a PicoHarp300 event timer. Measurements were carried out under vacuum (<5×10^(-2) mbar) and air, as discussed in the main text. Time-Resolved Photoluminescence Fitting A least-squares fit was carried out on the highest-fluence PL decay using a stretched exponential of the form I=I_0 e^(-(t/t_char )^ß ) between 0 – 150 ns, and the average decay lifetime is calculated as t_av=(t_char/ß)G(1/ß). Optical-Pump Terahertz-Probe Spectroscopy An amplified laser system (Spectra Physics, MaiTai - Ascend - Spitfire) with a central wavelength 800 nm, 35 fs pulse duration and 5 kHz repetition rate was used to generate THz radiation via the inverse spin hall effect8and was detected using free-space electro-optic sampling with a 1 mm-thick ZnTe (110) crystal, a Wollaston prism and a pair of balanced photodiodes. The THz pulse was measured in transmission geometry. The pump beam was frequency-doubled to 400nm by a ß-barium- borate (BBO) crystal. Measurements were carried out under low vacuum (< 10-2 mbar). Charge-carrier mobilities were calculated from the initial transmitted signal at time t = 0 ps, at fluences of 4.9, 12.5, 25 µJcm^(-2).