. Broader ContextThin film photovoltaics (PV), based on materials that absorb light 10-100 times more efficiently than crystalline silicon, has the potential to drive down PV module cost by increasing efficiency and requiring less raw material. Currently, the market for thin film PV is dominated by CdTe and CuIn x Ga 1-x Se 2 technologies, which suffer from concerns of toxicity (Cd) or rarity (Te, In) when considering terawatt-scale deployment. As an alternative to these technologies, researchers have turned to studying new absorber materials that exhibit equivalent light absorbing properties but are comprised of Earth-abundant elements. In this work, we explore the properties of a thin film III-N analog, ZnSnN 2 , that until recently has received little attention in the literature. Classification as a III-N analog is advantageous for PV applications, considering that III-N materials are well-known for their stability. ZnSnN 2 possesses a direct bandgap and large absorption coefficient in a PV-relevant energy range, in addition to being composed of abundant and non-toxic elements. However, a few key optoelectronic properties (e.g. doping control and exact bandgap) of this material are not well understood. If this challenge is addressed, ZnSnN 2 has excellent potential as an absorber material for Earth-abundant thin film PV. AbstractZnSnN 2 is an Earth-abundant semiconductor analogous to the III-Nitrides with potential as a solar absorber due to its direct bandgap, steep absorption onset, and disorder-driven bandgap tunability. Despite these desirable properties, discrepancies in the fundamental bandgap and degenerate n-type carrier density have been prevalent issues in the limited amount of literature available on this material. Using a combinatorial RF co-sputtering approach, we have been able to explore a growth-temperature-composition space for Zn 1+x Sn 1-x N 2 over the ranges 35-340• C and 0.30-0.75 Zn/(Zn+Sn). In this way, we were able to identify an optimal set of deposition parameters for obtaining as-deposited films with wurtzite crystal structure and carrier density as low as 1.8 x 10 18 cm -3 . Films grown at 230• C with Zn/(Zn+Sn) = 0.60 were found to have the largest grain size overall (70 nm diameter on average) while also exhibiting low carrier density (3 x 10 18 cm -3 ) and high mobility (8.3 cm 2

Electron-beam-induced damages in methylammonium lead triiodide (MAPbI3) perovskite thin films were studied by cathodo­luminescence (CL) spectroscopy. We find that high-energy electron beams can significantly alter perovskite properties through two distinct mechanisms: (1) defect formation caused by irradiation damage and (2) phase transformation induced by electron-beam heating. The former mechanism causes quenching and broadening of the excitonic peaks in CL spectra, whereas the latter results in new peaks with higher emission photon energy. The electron-beam damage strongly depends on the electron-beam irradiation conditions. Although CL is a powerful technique for investigating the electronic properties of perovskite materials, irradiation conditions should be carefully controlled to avoid any significant beam damage. In general, reducing acceleration voltage and probing current, coupled with low-temperature cooling, is more favorable for CL characterization and potentially for other scanning electron-beam-based techniques as well. We have also shown that the stability of perovskite materials under electron-beam irradiation can be improved by reducing defects in the original thin films. In addition, we investigated effects of electron-beam irradiation on formamidinium lead triiodide (FAPbI3) and CsPbI3 thin films. FAPbI3 shows similar behavior as MAPbI3, whereas CsPbI3 displays higher resistance to electron-beam damage than its organic–inorganic hybrid counterparts. Using CsPbI3 as a model material, we observed nonuniform luminescence in different grains of perovskite thin films. We also discovered that black-to-yellow phase transformation of CsPbI3 tends to start from the junctions at grain boundaries.

Single-phase, spinel zinc stannate (Zn2SnO4) thin films were grown by rf magnetron sputtering onto glass substrates. Uniaxially oriented films with resistivities of 10−2–10−3 Ω cm, mobilities of 16–26 cm2/V s, and n-type carrier concentrations in the low 1019 cm−3 range were achieved. X-ray diffraction peak intensity studies established the films to be in the inverse spinel configuration. Sn119 Mössbauer studies identified two octahedral Sn sites, each with a unique quadrupole splitting, but with a common isomer shift consistent with Sn+4. A pronounced Burstein–Moss shift moved the optical band gap from 3.35 to as high as 3.89 eV. Density-of-states effective mass, relaxation time, mobility, Fermi energy level, and a scattering parameter were calculated from resistivity, Hall, Seebeck, and Nernst coefficient transport data. Effective-mass values increased with carrier concentration from 0.16 to 0.26 me as the Fermi energy increased from 0.2 to 0.9 eV above the conduction-band minimum. A bottom-of-the-band effective-mass value of 0.15 me is in good agreement with local density approximation calculations. Temperature-dependent transport measurements and calculated scattering parameters correlated well with ionized impurity scattering with screening by free electrons for highly degenerate films.