Electrical transport parameters for active layers in silicon (Si) wafer solar cells are determined from free carrier optical absorption using non-contacting optical Hall effect measurements. Majority carrier transport parameters [carrier concentration (N), mobility (μ), and conductivity effective mass (m*)] are determined for both the n-type emitter and p-type bulk wafer Si of an industrially produced aluminum back surface field (Al-BSF) photovoltaic device. From measurements under 0 and ±1.48 T external magnetic fields and nominally “dark” conditions, the following respective [n, p]-type Si parameters are obtained: N = [(3.6 ± 0.1) × 10¹⁸ cm⁻³, (7.6 ± 0.1) × 10¹⁵ cm⁻³]; μ = [166 ± 6 cm²/Vs, 532 ± 12 cm²/Vs]; and m* = [(0.28 ± 0.03) × m_e, (0.36 ± 0.02) × m_e]. All values are within expectations for this device design. Contributions from photogenerated carriers in both regions of the p-n junction are obtained from measurements of the solar cell under “light” 1 sun illumination (AM1.5 solar irradiance spectrum). From analysis of combined dark and light optical Hall effect measurements, photogenerated minority carrier transport parameters [minority carrier concentration (Δp or Δn) and minority carrier mobility (μ_h or μ_e)] under 1 sun illumination for both n- and p-type Si components of the solar cell are determined. Photogenerated minority carrier concentrations are [(7.8 ± 0.2) × 10¹⁶ cm⁻³, (2.2 ± 0.2) × 10¹⁴ cm⁻³], and minority carrier mobilities are [331 ± 191 cm²/Vs, 766 ± 331 cm²/Vs], for the [n, p]-type Si, respectively, values that are within expectations from literature. Using the dark majority carrier concentration and the effective equilibrium minority carrier concentration under 1 sun illumination, minority carrier effective lifetime and diffusion length are calculated in the n-type emitter and p-type wafer Si with the results also being consistent with literature. Solar cell device performance parameters including photovoltaic device efficiency, open circuit voltage, fill factor, and short circuit current density are also calculated from these transport parameters obtained via optical Hall effect using the diode equation and PC1D solar cell simulations. The calculated device performance parameters are found to be consistent with direct current-voltage measurement demonstrating the validity of this technique for electrical transport property measurements of the semiconducting layers in complete Si solar cells. To the best of our knowledge, this is the first method that enables determination of both minority and majority carrier transport parameters in both active layers of the p-n junction in a complete solar cell.

Electrical transport properties [carrier concentration (N), mobility (μ), effective mass (m*), resistivity (ρ), and scattering time (τ)] are deduced from free carrier optical absorption using noncontacting optical Hall effect measurements. Here, we use this technique to determine N, μ, and m* for semiconductor absorber materials for photovoltaic (PV) devices. As case studies, PV component materials including thin-film methylammonium lead iodide, cadmium telluride, and copper indium diselenide as well as silicon wafers are characterized. Optical Hall effect measurements involve collecting long wavelength ellipsometric spectra under the application of an external magnetic field to determine N and μ for these thin films, and N, μ, and m* for the silicon wafers. ρ and τ are also determined for each sample from N, μ, and m* using the Drude model. In all cases, an additional transport parameter measurement is accessible relative to standard optical measurements alone even for the PV absorber materials having low free carrier absorption. As the technique is noncontacting, it could be very useful for the determination of transport properties of layers in complex multilayer stacks such as those in thin film and wafer-based PV devices.

Tin doped indium oxide (In ₂ O ₃ :Sn (ITO)) thin films RF sputtered under similar conditions on soda lime glass and single crystal silicon wafers (c-Si) are used to study near infrared optical absorption variations during film growth. The presence of strong free carrier absorption and phonon absorption in the low photon energy spectral range provides an opportunity to disentangle tailing effects extending in the near infrared to visible spectral range. Toward that end, a model describing ITO film optical properties in the form of the complex dielectric function ( ε = ε ₁ + i ε ₂ ) from ex situ ellipsometry collected over 0.4 to 4.1 meV, 0.035 to 0.4 eV, and 0.75 to 5.89 eV spectral range is developed to describe these features along with other higher energy electronic transitions. In situ real time spectroscopic ellipsometry (RTSE) from 0.75 to 5.89 eV is used to track changes film structure and optical response during thin film growth. Optical emission spectroscopy indicates the plasma is very stable during deposition implying that film property changes with thickness are not correlated with changes in plasma chemistry. Film resistivity ( ρ ), mobility ( µ ), scattering time ( τ ), and carrier concentration ( n ) are determined from the free carrier absorption component of ε . Increased near infrared absorption manifested in ε obtained from RTSE data analysis is hypothesized to originate from enhancement of OH-group phonon absorption due to the presence of water molecules in the chamber at the beginning of growth.

Non-contacting optical probes based on spectroscopic ellipsometry or reflectance measurements are used to predict photovoltaic (PV) device performance and to diagnose optical and electronic losses. Optical modeling of aluminum back surface field (Al-BSF) silicon, thin film cadmium telluride (CdTe), and hybrid organic inorganic lead halide based perovskite (FA_1−xCs_xPbI₃) solar cell technologies are reviewed. Using the near infrared (IR) to ultraviolet (UV) optical properties of PV device component materials and the device structures as input, external quantum efficiency (EQE) spectra are simulated for Al-BSF, CdTe, and perovskite solar cells for comparison with experimental EQE and short circuit current density (J_SC). Optical Hall effect measurements of Al-BSF PV determine majority and minority carrier transport properties in the n+ emitter and p-type wafer silicon; from this information open circuit voltage (V_OC), fill factor (FF), J_SC, and power conversion efficiency (PCE) are calculated and agree well with direct current-voltage (J-V) electrical measurement. An IR-extended optical model for Al-BSF silicon PV includes coherent multiple reflections, ray tracing optics, and diffuse scattering and is applicable as a baseline for developing optical and thermal management strategies. Analysis of EQE for CdTe based solar cells with selenium alloying (CdSe_1−yTe_y) enables determination of absorber composition after full device processing. EQE modeling for perovskite solar cells includes the ability to account for sub gap absorption measured in films but not present in the solar cell absorber and incomplete photogenerated carrier collection in the PV device.