Inorganic Nanocomposites of n- and p-Type Semiconductors: A New Generation of 3D Solar Cells
01 / 2002 - 04 / 2006
The major drawback of the present generation of photovoltaic solar cells is their laborious, energy consuming, and costly production. Therefore, a completely new approach is desired. With the advent of dye-sensitized (Gr䴺el-type) solar cells, C60/polymer, and hybrid CdSe / polymer bulk heterojunctions challenging alternatives are offered, although serious complications have still to be solved. A major concern in these alternatives is their poor stability when operating in full sunlight. The cells must be sealed completely against oxygen and water. All-solid, completely inorganic, bulk heterojunctions do not require expensive sealing and have been pursued with limited success so far. Here we report a new approach towards what we call the 3D solar cell concept. We employed Atomic-Layer Chemical Vapour Deposition (AL-CVD) and spray pyrolysis for infiltration of CuInS2 inside the pores of nanostructured TiO2. In this way it is possible to obtain a nanometer-scale interpenetrating network between n-type TiO2 and p-type CuInS2. The efficiency of CuInS2 (CIS) solar cells is determined by the presence of native (extrinsic) lattice defects. A detailed study of native defects in CuInS2 (CIS) thin films is necessary for optimisation of photovoltaic solar cells based on this material. These defects introduce energy levels in the band gap, which determine the conductivity type, and the minority carrier lifetime. In this study we apply different characterization methods to elucidate the defect chemistry of CIS. The CuInS2 films are investigated by X-ray diffraction, Raman spectroscopy, photoluminescence (PL) spectroscopy, Impedance Spectroscopy (IS), and Deep-Level Transient Spectroscopy (DLTS). Spray pyrolysis offers a cheap alternative to deposit semiconductor thin-films, which is the topic of the present study. Spray pyrolysis is a suitable technique to obtain thin film coatings at minimal costs. Careful selection of the deposition parameters results in a homogeneous deposition. The thin films obtained have adequate properties, which make them suitable for use in solar cells. This 3D solar cell, based on the nanocomposite TiO2 : CuInS2, opens up a new direction towards cheap and efficient PV devices.