Robert C. Reedy

We show a method for making a self-aligned selective emitter by annealing aluminum grid lines above the SiAl eutectic temperature, and study the recombination properties using lifetime measurements. The dark saturation current density at the metal contact (J _0,metal ) is determined as a function of minority carrier density using photoconductive decay. After annealing at 600 °C, J _0,metal decreases from 1800 fA cm ^-2 to 500 fA cm ^-2 at an injection level of 1E15 cm ^-3 . This value of J _0,metal would correspond to a very low emitter recombination contribution of ~10 - 25 fA cm ^-2 for a front metal grid with area coverage of 2 - 5%. In addition, J _0,metal is found to be injection dependent. A low contact resistivity of ~0.1 mOhm cm ^-2 is obtained from transmission line measurement (TLM).

The Sutter's Mill (SM) carbonaceous chondrite fell in California on April 22, 2012. The cosmogenic radionuclide data indicate that Sutter's Mill was exposed to cosmic rays for 0.082 ± 0.008 Myr, which is one of the shortest ages for C chondrites, but overlaps with a small cluster at approximately 0.1 Myr. The age is significantly longer than proposed ages that were obtained from cosmogenic noble gas concentrations, which have large uncertainties due to trapped noble gas corrections. The presence of neutron‐capture ⁶⁰Co and ³⁶Cl in SM indicates a minimum preatmospheric radius of approximately 50 cm, and is consistent with a radius of 1–2 m, as derived from the fireball observations. Although a large preatmospheric size was proposed, one fragment (SM18) contains solar cosmic ray–produced short‐lived radionuclides, such as ⁵⁶Co and ⁵¹Cr. This implies that this specimen was less than 2 cm from the preatmospheric surface of Sutter's Mill. Although this conclusion seems surprising, it is consistent with the observation that the meteoroid fragmented high in the atmosphere. The presence of SCR‐produced nuclides is consistent with the high SCR fluxes observed during the last few months before the meteorite's fall, when its orbit was less than 1 AU from the Sun.

Most recent gains in CdTe photovoltaic (PV) device efficiency have been in short-circuit current density (Jsc) and fill factor (FF), rather than open-circuit voltage (Voc). Because Jsc is nearing its theoretical limit, further improvements in device efficiency will require increasing Voc beyond 860 mV and increasing FF. Voc and FF may be improved by increasing both the carrier concentration and minority-carrier lifetime of the CdTe. However, Voc may be limited for other reasons, including Fermi-level pinning and surface recombination. In this study, we used doped CdTe single crystals to test whether higher carrier concentration and lifetime can overcome traditional Voc barriers. In our work to date, we have fabricated heterojunction CdTe PV cells with Voc up to 929 mV, FF of ~60%, and efficiencies of 10%.