Effects of surface nanostructuring and impurity doping on ultrafast carrier dynamics of silicon photovoltaic cells: a pump-probe study

Abstract

We present femtosecond optical pump-terahertz probe studies on the ultrafast dynamical processes of photo-generated charge carriers in silicon photovoltaic cells with various nanostructured surfaces and doping densities. The pump-probe measurements provide direct insight on the lifetime of photo-generated carriers, frequency-dependent complex dielectric response along with photoconductivity of silicon photovoltaic cells excited by optical pump pulses. A lifetime of photo-generated carriers of tens of nanosecond is identified from the time-dependent pump-induced attenuation of the terahertz transmission. In addition, we find a large value of the imaginary part of the dielectric function and of the real part of the photoconductivity in silicon photovoltaic cells with micron length nanowires. We attribute these findings to the result of defect-enhanced electron–photon interactions. Moreover, doping densities of phosphorous impurities in silicon photovoltaic cells are also quantified using the Drude–Smith model with our measured frequency-dependent complex photoconductivities.

Effect of IT-M doping on charge transfer and ultrafast carrier dynamics of ternary organic solar cell materials

“…In contrast to the conventional optoelectronic measurements, in which the charge transport properties are obtained by measuring the current density-voltage characteristics under illumination, optical pump time-resolved terahertz (THz) probe spectroscopy provides the possibility to accurately resolve the ultrafast dynamics of photo-excited charge carriers, the frequency-resolved complex refractive index, the dielectric response, and the photoconductivity in semiconductors or insulators [20][21][22][23][24][25][26][27]. By analyzing the measured frequency-resolved complex photoconductivity with a classical Drude-like model, charge carrier density and scattering time, which are the fundamental physical properties of the material, are obtained [22].…”

First- and second-order photon–phonon interactions and optical parameters of ZnTe crystal: a broadband terahertz time-domain spectroscopy study

“…Combining the characteristics of THz radiation with the ultrafast spectroscopy technique, THz time-domain spectroscopy (THz-TDS) provides the possibility to study the THz response of charge carriers, lattice vibrations and polarons in materials within the time scales of sub-picosecond. Owing to the advantages of time-resolved THz spectroscopy, fundamental physical properties including the ultrafast relaxation time of hot-carriers, frequency-resolved complex photoconductivity and photon-induced dielectric response, along with charge carrier densities and scattering times of both bulk and nanoscale materials have been well studied by using THz-TDS measurements [4][5][6][7][8][9][10][11][12][13][14]. In addition to the studies on the electronic properties, interactions between THz photon and lattice vibrations in CdTe and ZnTe crystal wafers have been investigated using THz-TDS measurements, in which THz absorption peaks with frequencies lower than 3 THz were obtained [15].…”

“…In most of the previous THz-TDS studies, the THz waves were generated either via nonlinear optical process using a non-Centro-symmetric crystal such as ZnTe as the working material [13,14] or based on the emission of photoconductive antenna [15]. Due to the strong phonon absorption of the nonlinear optical crystals [16][17][18] and the complicated geometry structures of photoconductive antenna, the bandwidths of these THz sources were limited in the range from 0.1 to 3 THz.…”