A comprehensive study of the room-temperature electrical and electrothermal transport of single-crystalline indium oxide (In 2 O 3) and indium tin oxide (ITO) films over a wide range of electron concentrations is reported. We measured the room-temperature Hall mobility μ H and Seebeck coefficient S of unintentionally doped and Sn-doped high-quality, plasma-assisted molecular-beam-epitaxy-grown In 2 O 3 for volume Hall electron concentrations n H from 7 × 10 16 cm −3 (unintentionally doped) to 1 × 10 21 cm −3 (highly Sn-doped, ITO). The resulting empirical S(n H) relation can be directly used in other In 2 O 3 samples to estimate the volume electron concentration from simple Seebeck coefficient measurements. The mobility and Seebeck coefficient were modeled by a numerical solution of the Boltzmann transport equation. Ionized impurity scattering and polar optical phonon scattering were found to be the dominant scattering mechanisms. Acoustic phonon scattering was found to be negligible. Fitting the temperature-dependent mobility above room temperature of an In 2 O 3 film with high mobility allowed us to find the effective Debye temperature (D = 700 K) and number of phonon modes (N OPML = 1.33) that best describe the polar optical phonon scattering. The modeling also yielded the Hall scattering factor r H as a function of electron concentration, which is not negligible (r H ≈ 1.4) at nondegenerate electron concentrations. Fitting the Hall-scattering-factor corrected concentration-dependent Seebeck coefficient S(n) for nondegenerate samples to the numerical solution of the Boltzmann transport equation and to widely used, simplified equations allowed us to extract an effective electron mass of m * = (0.30 ± 0.03)m e (with free electron mass m e). The modeled mobility and Seebeck coefficient based on polar optical phonon and ionized impurity scattering describes the experimental results very accurately up to electron concentrations of 10 19 cm −3 , and qualitatively explains a mobility plateau or local maximum around 10 20 cm −3. Ionized impurity scattering with doubly charged donors best describes the mobility in our unintentionally doped films, consistent with oxygen vacancies as unintentional shallow donors, whereas singly charged donors best describe our Sn-doped films. Our modeling yields a (phonon-limited) maximum theoretical drift mobility and Hall mobility of μ = 190 cm 2 /Vs and μ H = 270 cm 2 /V s, respectively. Simplified equations for the Seebeck coefficient describe the measured values in the nondegenerate regime using a Seebeck scattering parameter of r = −0.55 (which is consistent with the determined Debye temperature), and provide an estimate of the Seebeck coefficient to lower electron concentrations. The simplified equations fail to describe the Seebeck coefficient around the Mott transition (n Mott = 5.5 × 10 18 cm −3) from nondegenerate to degenerate electron concentrations, whereas the numerical modeling accurately describes this region.

Liquid phase crystallized silicon on glass with a thickness of (10–40) μm has the potential to reduce material costs and the environmental impact of crystalline silicon solar cells. Recently, wafer quality open circuit voltages of over 650 mV and remarkable photocurrent densities of over 30 mA/cm2 have been demonstrated on this material, however, a low fill factor was limiting the performance. In this work we present our latest cell progress on 13 μm thin poly-crystalline silicon fabricated by the liquid phase crystallization directly on glass. The contact system uses passivated back-side silicon hetero-junctions, back-side KOH texture for light-trapping and interdigitated ITO/Ag contacts. The fill factors are up to 74% and efficiencies are 13.2% under AM1.5 g for two different doping densities of 1 · 1017/cm3 and 2 · 1016/cm3. The former is limited by bulk and interface recombination, leading to a reduced saturation current density, the latter by series resistance causing a lower fill factor. Both are additionally limited by electrical shading and losses at grain boundaries and dislocations. A small 1 × 0.1 cm2 test structure circumvents limitations of the contact design reaching an efficiency of 15.9% clearly showing the potential of the technology.

Electrokinetic charging of aqueous microjets was characterized by measuring streaming currents as a function of sodium iodide salt concentration. Measured streaming currents at high salt concentrations (up to 0.5 M) varied nonmonotonically with the jet velocity and can be explained by a multipolar charge distribution at the nozzle-water interface. In the case of potassium fluoride no multipolar charge distribution is observed. Electrokinetic potentials were estimated from the streaming currents, under the assumption that all excess charges are confined within the liquid jet. Measured photoelectron spectra indicate much smaller streaming potentials. To resolve the apparent discrepancy, we propose that a significant fraction of excess charges evaporates in the form of ion-water clusters.

Liquid phase crystallization of silicon (LPC-Si) on glass is a promising method to produce high quality multi-crystalline Si films with macroscopic grains. In this study, we report on recent improvements of our interdigitated back-contact silicon heterojunction contact system (IBC-SHJ), which enabled open circuit voltages as high as 661 mV and efficiencies up to 14.2% using a 13 µm thin n-type LPC-Si absorbers on glass. The influence of the BSF width on the cell performance is investigated both experimentally and numerically. We combine 1D optical simulations using GenPro4 and 2D electrical simulations using Sentaurus™ TCAD to determine the optical and electrical loss mechanisms in order to estimate the potential of our current LPC-Si absorbers. The simulations reveal an effective minority carrier diffusion length of 26 µm and further demonstrate that a doping concentration of 4×10 16 cm-3 and a back surface field width of 60 µm are optimum values to further increase cell efficiencies.

Thin crystalline silicon solar cells prepared directly on glass substrates by means of liquid-phase crystallization of the absorber utilize only a small fraction of the silicon material used by standard wafer-based silicon solar cells. The material consists of large crystal grains of up to square centimeter area and results in solar cells with open-circuit voltages of 650 mV, which is comparable with results achieved with multi-crystalline silicon wafers. We give a brief status update and present new results on the electronic interface and bulk properties. The interrelation between surface passivation and additional hydrogen plasma passivation is investigated for p-type and n-type absorbers with different doping concentrations. Internal quantum efficiency measurements from both sides on bifacial solar cells are used to extract the bulk-diffusion length and surface-recombination velocity. Finally, we compare various types of solar cell devices based on 10 μm thin crystalline silicon, where conversion efficiencies of 11-12% were achieved with p-type and n-type liquid-phase crystallized absorbers on glass.