Characterization of amorphous Si, CdTe, and Cu(InGa)Se 2 -based thin-film solar cells is described with focus on the deviations in device behavior from standard device models. Quantum efficiency (QE), current-voltage (J-V), and admittance measurements are reviewed with regard to aspects of interpretation unique to the thin-film solar cells. In each case, methods are presented for characterizing parasitic effects common in these solar cells in order to identify loss mechanisms and reveal fundamental device properties. Differences between these thin-film solar cells and idealized devices are largely due to a high density of defect states in the absorbing layers and to parasitic losses due to the device structure and contacts. There is also commonly a voltage-dependent photocurrent collection which affects J-V and QE measurements. The voltage and light bias dependence of these measurements can be used to diagnose specific losses. Examples of how these losses impact the QE, J-V, and admittance characterization are shown for each type of solar cell.Solar cell operation, either crystalline or thin film, can be described by identifying loss mechanisms. These can be divided into three categories. First are recombination losses which limit the open-circuit voltage V OC . Second are parasitic losses, such as series resistance, shunt conductance, and voltage-dependent current collection, which primarily impact the fill factor (FF), but can also reduce short circuit current J SC and V OC . Finally, there are optical losses which limit generation of carriers and, therefore, J SC . We focus on losses largely unique to TFSCs.Physical and electrical properties of TFSCs which cause them to have different losses from the standard 'textbook' crystalline Si (c-Si) cells include: * TFSC absorber layers have much higher absorption coefficients than c-Si so a large fraction of the photogeneration occurs near the interface and in the high field space charge region (SCR). This enables high currents, even with relatively small collection lengths; * the semiconductor films often have a range of shallow and deep defect levels or defect bands within the bandgap. These result from imperfect crystallinity or amorphous structure and from the use of low-cost materials and processes optimized for high throughput and low cost as much as for high device efficiency. This can create different recombination mechanisms than radiative band-to-band recombination commonly found in ideal crystalline semiconductor devices; * poor minority carrier lifetime, due to the above factors, leads to increased reliance on the electric field for sufficient minority carrier collection rather than diffusion alone. This often results in voltage-dependent collection of light-generated current; * TFSCs are heterojunction device structures with high densities of defect states at interfaces which can provide a path for interface recombination; * the grain boundaries in polycrystalline Cu(InGa)Se 2 and CdTe devices may act as high recombination surfaces or shunt paths. This l...

The creation of a suitable inorganic colloidal nanocrystal ink for use in a scalable coating process is a key step in the development of low-cost solar cells. Here, we present a facile solution synthesis of chalcopyrite CuInSe 2 nanocrystals and demonstrate that inks based on these nanocrystals can be used to create simple solar cells, with our first cells exhibiting an efficiency of 3.2% under AM1.5 illumination. We also report the first solution synthesis of uniform hexagonal shaped single crystals CuInSe 2 nanorings by altering the synthesis parameter.

The drive-level capacitance profiling technique has been applied to ZnO/CdS/CuIn1−xGaxSe2/Mo solar cell devices, in order to study properties of defects in the CuIn1−xGaxSe2 film. Properties studied include the spatial uniformity, bulk defect response, carrier density, and light-induced metastable effects. These results indicate that previous estimates of carrier densities, from C–V profiling, may be significantly overestimated. In addition, a defect response previously thought to be located at the interface is observed to exist throughout the bulk material. Finally, an infrared light-soaking treatment is demonstrated to induce metastable changes in the bulk CuIn1−xGaxSe2 film. Hence, the drive-level capacitance profiling technique provides valuable insights into these films. Herein, the technique itself is fully explained, compared to other junction capacitance methods, and its utility is demonstrated using numerical simulation.

Optical constants of polycrystalline thin film CuIn1−xGaxSe2 alloys with Ga/(Ga+In) ratios from 0 to 1 have been determined by spectroscopic ellipsometry over an energy range of 0.75–4.6 eV. CuIn1−xGaxSe2 films were deposited by simultaneous thermal evaporation of elemental copper, indium, gallium and selenium. X-ray diffraction measurements show that the CuIn1−xGaxSe2 films are single phase. Due to their high surface roughness, the films are generally not suitable for ellipsometer measurements. A method is presented in which spectroscopic ellipsometer measurements were carried out on the reverse side of the CuIn1−xGaxSe2 films immediately after peeling them from Mo-coated soda lime glass substrates. A detailed description of multilayer optical modeling of ellipsometric data, generic to ternary chalcopyrite films, is presented. Accurate values of the refractive index and extinction coefficient were obtained and the effects of varying Ga concentrations on the electronic transitions are presented.