Generation-dependent charge carrier transport in Cu(In,Ga)Se 2/CdS/ZnO thin-film solar-cells

The following article appeared in Journal of Applied Physics 113.4 (2013): 044515 and may be found at http://scitation.aip.org/content/aip/journal/jap/113/4/10.1063/1.4788827Cross section electron-beam induced current (EBIC) and illumination- dependent current voltage (IV) measurements show that charge carrier transport in Cu(In,Ga)Se2 (CIGSe)/CdS/ZnO solar-cells is generation-dependent. We perform a detailed analysis of CIGSe solar cells with different CdS layer thicknesses and varying Ga-content in the absorber layer. In conjunction with numerical simulations, EBIC and IV data are used to develop a consistent model for charge and defect distributions with a focus on the heterojunction region. The best model to explain our experimental data is based on a p+ layer at the CIGSe/CdS interface leading to generation-dependent transport in EBIC at room temperature. Acceptor-type defect states at the CdS/ZnO interface cause a significant reduction of the photocurrent in the red-light illuminated IV characteristics at low temperatures (red kink effect). Shallow donor-type defect states at the p+ layer/CdS interface of some grains of the absorber layer are responsible for grain specific, i.e., spatially inhomogeneous, charge carrier transport observed in EBIC

IBPOWER Project, Intermediate band materials and solar cells for photovoltaics with high efficiency and reduced cost

IBPOWER is a Project awarded under the 7th European Framework Programme that aims to advance research on intermediate band solar cells (IBSCs). These are solar cells conceived to absorb below bandgap energy photons by means of an electronic energy band that is located within the semiconductor bandgap, whilst producing photocurrent with output voltage still limited by the total semiconductor bandgap. IBPOWER employs two basic strategies for implementing the IBSC concept. The first is based on the use of quantum dots, the IB arising from the confined energy levels of the electrons in the dots. Quantum dots have led to devices that demonstrate the physical operation principles of the IB concept and have allowed identification of the problems to be solved to achieve actual high efficiencies. The second approach is based on the creation of bulk intermediate band materials by the insertion of an appropriate impurity into a bulk semiconductor. Under this approach it is expected that, when inserted at high densities, these impurities will find it difficult to capture electrons by producing a breathing mode and will cease behaving as non-radiative recombination centres. Towards this end the following systems are being investigated: a) Mn: In1-xGax N; b) transition metals in GaAs and c) thin films

Buffer free Cu In,Ga Se2 solar cells by near surface ion implantation

High efficiency Cu In,Ga Se2 thin film solar cells typically include CdS buffer layers deposited in a chemical bath. In this work, Cu In,Ga Se2 devices are presented in which the CdS buffer layer was omitted completely. Instead, low energy ion implantation of group II elements Cd, Zn, and Mg is applied in order to establish an n type surface layer in p type Cu In,Ga Se2 absorber layers. Therefore, thermal annealing procedures were developed which lead to a full recovery of the implantation induced defects and simultaneously minimize the diffusion of the dopants. Such a treatment is shown to provide high quality p n junction functionality and buffer free Cu In,Ga Se2 thin film solar cells with opencircuit voltages close to 600 mV and efficiencies exceeding 1