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The development of tandem photovoltaics and photoelectrochemical solar cells requires new absorber materials with bandgaps in the range of ≈1.5–2.3 eV, for use in the top cell paired with a narrower‐gap bottom cell. An outstanding challenge is finding materials with suitable optoelectronic and defect properties, good operational stability, and synthesis conditions that preserve underlying device layers. This study demonstrates the Zintl phosphide compound CaZn2P2 as a compelling candidate semiconductor for these applications. Phase‐pure, ≈500 nm‐thick CaZn2P2 thin films are prepared using a scalable reactive sputter deposition process at growth temperatures as low as 100 °C, which is desirable for device integration. Ultraviolet‐visible spectroscopy shows that CaZn2P2 films exhibit an optical absorptivity of ≈104 cm−1 at ≈1.95 eV direct bandgap. Room‐temperature photoluminescence (PL) measurements show near‐band‐edge optical emission, and time‐resolved microwave conductivity (TRMC) measurements indicate a photoexcited carrier lifetime of ≈30 ns. CaZn2P2 is highly stable in both ambient conditions and moisture, as evidenced by PL and TRMC measurements. Experimental data are supported by first‐principles calculations, which indicate the absence of low‐formation‐energy, deep intrinsic defects. Overall, this study shall motivate future work integrating this potential top cell absorber material into tandem solar cells. [ABSTRACT FROM AUTHOR]

A trap‐corrected bias–temperature–stress (TraC‐BTS) method to quantify the kinetics of ion migration in dielectrics based on capacitance–voltage measurements is presented. The method is based on the extraction of flatband potential (Vfb) shifts in metal–insulator–semiconductor test structures an enables the reliability assessment of semiconductor dielectrics and solar cells. Herein, it is shown that carrier trapping in the dielectric must be accounted for, as it strongly affects the measurement of flatband potential in silicon‐nitride‐based capacitors. This effect is corrected by isolating the contribution of trapping on Vfb using contamination‐free control devices. A specific drift‐diffusion model of the ion kinetics presented herein allows the extraction of ion diffusivity. An Arrhenius relationship is obtained for sodium diffusivity in silicon nitride in a temperature range from 30 °C to 90 °C at an electric field of 1 MV cm−1, yielding a prefactor D0=1×10−14 cm2 s−1 and an activation energy Ea=0.14 eV, with a 95% confidence interval of [0.07,0.21] eV for the diffusivity. These quantitative kinetics confirm that silicon nitride may be a poor sodium migration barrier under a significant electric field. [ABSTRACT FROM AUTHOR]

Solar cells based on n-type multicrystalline silicon (mc-Si) wafers are a promising path to reduce the cost per kWh of photovoltaics; however, the full potential of the material and how to optimally process it are still unknown. Process optimization requires knowledge of the response of the metalsilicide precipitate distribution to processing, which has yet to be directly measured and quantified. To supply this missing piece, we use synchrotron-based micro-X-ray fluorescence (µ-XRF) to quantitatively map >250 metal-rich particles in n-type mc-Si wafers before and after phosphorus diffusion gettering (PDG).We find that 820 °C PDG is sufficient to remove precipitates of fast-diffusing impurities and that 920 °C PDG can eliminate precipitated Fe to below the detection limit of µ-XRF. Thus, the evolution of precipitated metal impurities during PDG is observed to be similar for n- and p-type mc-Si, an observation consistent with calculations of the driving forces for precipitate dissolution and segregation gettering. Measurements show that minority-carrier lifetime increases with increasing precipitate dissolution from 820 °C to 880°C PDG, and that the lifetime after PDG at 920 °C is between the lifetimes achieved after 820 °C and 880 °C PDG. [ABSTRACT FROM AUTHOR]

Chromium (Cr) can degrade silicon wafer-based solar cell efficiencies at concentrations as low as 1010cm-3. In this contribution, we employ synchrotron-based X-ray fluorescence microscopy to study chromium distributions in multicrystalline silicon in as-grown material and after phosphorous diffusion. We complement quantified precipitate size and spatial distribution with interstitial Cr concentration and minority carrier lifetime measurements to provide insight into chromium gettering kinetics and offer suggestions for minimizing the device impacts of chromium. We observe that Cr-rich precipitates in as-grown material are generally smaller than iron-rich precipitates and that Cri point defects account for only one-half of the total Cr in the as-grown material. This observation is consistent with previous hypotheses that Cr transport and CrSi2 growth are more strongly diffusion-limited during ingot cooling. We apply two phosphorous diffusion gettering profiles that both increase minority carrier lifetime by two orders of magnitude and reduce [Cri] by three orders of magnitude to ≈1010cm-3. Some Cr-rich precipitates persist after both processes, and locally high [Cri] after the high-temperature process indicates that further optimization of the chromium gettering profile is possible. [ABSTRACT FROM AUTHOR]

The light-emitting diodes (LEDs) used in indoor testing of perovskite solar cells do not expose them to the levels of ultraviolet (UV) radiation that they would receive in actual outdoor use. We report degradation mechanisms of p-i-n–structured perovskite solar cells under unfiltered sunlight and with LEDs. Weak chemical bonding between perovskites and polymer hole-transporting materials (HTMs) and transparent conducting oxides (TCOs) dominate the accelerated A-site cation migration, rather than direct degradation of HTMs. An aromatic phosphonic acid, [2-(9-ethyl-9H-carbazol-3-yl)ethyl]phosphonic acid (EtCz3EPA), enhanced bonding at the perovskite/HTM/TCO region with a phosphonic acid group bonded to TCOs and a nitrogen group interacting with lead in perovskites. A hybrid HTM of EtCz3EPA with strong hole-extraction polymers retained high efficiency and improved the UV stability of perovskite devices, and a champion perovskite minimodule—independently measured by the Perovskite PV Accelerator for Commercializing Technologies (PACT) center—retained operational efficiency of >16% after 29 weeks of outdoor testing. [ABSTRACT FROM AUTHOR]

Module reliability and service lifetime are critical factors in improving photovoltaic system performance and reducing the levelized cost of electricity (LCOE). Soldering and lamination of the cell impart residual stresses that persist over time and superimpose additional loads during operation. This paper demonstrates the use of X-ray Topography (XRT) to image in-situ the dynamic response of a glass/backsheet mini-module upon drying at elevated temperature after saturation at humidity levels compatible with accelerated testing. The local water content in the encapsulant is also determined in-situ over time via Water Reflectometric Detection (WaRD), with diffusion of water in the front (glass side) and rear (backsheet side) resolved. As water diffuses out from the back of the glass/backsheet module, the cell curves towards the backsheet concomitantly. We find that the cell edges deflect 40 μm out-of-plane with respect to its center while the encapsulant dries, compared to ∼100 μm deflection when heating from 25 °C to 85 °C. The local cell deflections (changes in cell orientation) are correlated with the dynamic loss of water in the backside encapsulant. We conclude that the observed cell deflections are the result of hygroscopic stress induced by the encapsulant upon moisture outdiffusion. Therefore, the cell experiences a continually changing stress state and curvature dependent on local humidity and temperature. Depending on cell architecture and interconnection, this "breathing" mode of the cell may induce wear out and fatigue of the interconnects, affect the electrical connection of cracked pieces or cause failure near the interconnected edges of two cells. • The mechanical response to moisture diffusion in Glass/Backsheet PV modules is detectable by lab-scale X-Ray Topography. • The effect of moisture on the mechanical state of the cell can be decoupled from the influence of temperature. • Moisture diffusion dynamically changes the curvature of the PV cell, increasing as moisture diffuses out of the encapsulant. • The dynamic mechanical response to moisture raises the question of daily humidity cycling in mechanical fatigue of the cell. [ABSTRACT FROM AUTHOR]

Spatial heterogeneities in the chemical makeup of thin film photovoltaic devices are pivotal in determining device efficiency. We report the in-plane spatial distribution and degree of chlorine incorporation in organic-inorganic lead halide perovskite absorbers by means of nondestructive synchrotron-based nanoprobe X-ray fluorescence. The presence of chlorine is positively identified in CH3NH3PbI3 films synthesized with Cl-containing precursors and as an impurity in some films synthesized with nominally Cl-free precursors. The impurity may be introduced from precursors or as contaminants during film synthesis. The films formed from Cl-containing precursors contain roughly an order of magnitude higher amount of chlorine, with Cl:I values greater than 0.02 found whether Cl is present in either the organic or the inorganic precursor for both one- and two-step fabrication processes. A spatial variation in the Cl incorporation is observed within single particles and as well as between particles within a given film, and the standard deviation of the Cl:I ratio across the films is up to 30% of the average value. Understanding and controlling the heterogeneous distribution of chlorine in hybrid perovskite layers may offer a path to improve their photovoltaic performance. [ABSTRACT FROM AUTHOR]