Polycrystalline thin film technology has shown great promise for low cost, high efficiency photovoltaics. To further increase the power efficiency, a firm understanding of microstructural properties of the devices is required. In this work, we investigate the inhomogeneous electrical and optical properties using local excitation techniques that generate excess carriers by a near-field light illumination or by a focused electron beam irradiation. The spatially resolved photocurrent images of n-CdS / p-CdTe devices obtained by both techniques show high carrier collection efficiencies at grain boundaries. A novel and complementary technique, photothermal induced resonance (PTIR), is also used to obtain absorption spectra and maps in the near-field over a broad range of wavelengths. In PTIR a wavelength tunable pulsed laser is used in combination with an atomic force microscope tip to detect the local thermal expansion induced by light absorption. Sub-micrometer thick lamella samples of CdTe solar cells are measured, and the variation of local band-gap is analyzed. We discuss the resolution and the sensitivity of the techniques in the range of photon energies close to the band gap.
Proceedings Title: 31st European Photovoltaic Solar Energy Conference and Exhibition(EU PVSEC 2015)
Conference Dates: September 14-18, 2015
Conference Location: Hamburg, -1
Pub Type: Conferences
photothermal induced resonance (PTIR), CdTe solar cells, band-gap, scanning photocurrent microscopy (SPCM), near-field scanning optical microscopy (NSOM)