Aluminium-doped zinc oxide thin film contacts for use in dye-sensitized solar cells

Aluminium-doped zinc oxide films are deposited for use in dye-sensitized solar cells. High temperature stability is achieved by varying the sputtering conditions, whilst maintaining high transmission. The most stable film of the set deposited increased to only 9.4 Ω/sq after heating in air at 400°C from 5.1 Ω/sq. Initial solar cells are made with encouraging efficiencies of 8.2% reported

Chemical incorporation of copper into indium selenide thin films

Indium selenide thin-films have been treated in a copper-containing chemical bath with the goal of forming a precursor layer capable of being converted into copper indium diselenide. The conversion process was carried out by annealing the layers in a tube furnace in the presence of selenium vapour. The phase content of the layers as a function of composition and annealing temperature has been investigated by Raman spectroscopy. It is concluded that copper selenide is formed during the chemical bath treatment and that during annealing the copper selenide reacts first with elemental selenium vapour and then with the indium selenide to form chalcopyrite CuInSe2. Secondary phases of CuIn3Se5 and Cu-Au ordered CuInSe2 have been detected in annealed copper-poor layers

Characterisation of a LBIC system by scanning of silicon solar cells and modules

A laser beam induced current (LBIC) system has been used as a non-destructive characterisation tool for photovoltaic (PV) devices. It provides a detailed twodimensional map of the current signal. Each data point in the map is generated by the laser beam scanning over the devices. The signal strength depends on the response of that particular area on which the laser beam is incident, thereby reflecting the absorption and collection characteristics of that local PV area. However, the magnitude of the measured signal, induced by modulated laser, is very small. Adjustment of set parameters, measurement variables and environmental influences may affect the measurement result and thus could lead to misinterpretation. The LBIC system at the Centre for Renewable Energy Systems Technology (CREST) is analysed for reliability and optimised. It is evident that with appropriate settings under controlled environmental conditions, the system can provide a highly repeatable measurement result

Accelerated testing of performance of thin film module

There is an interest in identifying localised effects when investigating durability of devices. The combination of tests might also have an influence on test results. This is investigated for single junction amorphous silicon modules. The modules were put under accelerated testing including thermal cycling, light soaking and annealing test. I-V measurement and LBIC system as characterisation tools are used to investigate the possible degradation occurring in the devices both before and after certain stages of the test. Results have shown that there is a difference between modules which have experienced light soaking before being exposed to thermal cycling, indicating that the initial light soaking resulted in a UV activation of the material, which then changed the durability of the lamination

Structural analysis of thin film silicon PV modules by means of large area laser beam induced current measurements

The spatial variation of key properties of large area silicon thin film PV modules is investigated using a Laser Beam Induced Current (LBIC) system. The system produces a very detailed current mapping of devices, allowing the identification of spatially varying structural defects of photovoltaic modules. It allows for efficient defect detection as well as investigations of localised performance variation. In this paper, the results are shown for large area single junction amorphous silicon modules from different manufacturers that have been installed outdoors for more than two years. Several defects are identified as probable sources of poor performance and low efficiency of some devices. Some of the major contributions to these defects are likely to occur during the production process while some are developed during outdoor exposure

Energy production of single junction amorphous silicon modules with varying i-Layer thickness

The energy production of a number of single junction amorphous silicon (a-Si) solar modules with different intrinsic layer thicknesses is investigated. This has been carried out through both indoor measurement and real operating condition monitoring outdoors. After 13 months of light exposure, the fully degraded and seasonally annealed states, can be seen. The results indicate that the thinnest devices do not necessarily have the lowest degradation. The thicker devices which have higher initial efficiency, however do suffer greater efficiency degradation. Experiment also shows that energy production does not follow the initial Standard Test Condition (STC) rated efficiency as the highest can be seen in thinner modules, which initially have much lower efficiencies

Multi-layer LBIC system for thin film PV module characterisation

Several non-destructive characterisation tools - solar simulator, LBIC, thermography - are used together to investigate the performance of and locate possible defects in TF silicon PV modules of different structures. A special module is investigated where all techniques are compared and good agreement is demonstrated

Alkali incorporation into solution processed CIGS precursor layers

Solution based ion-exchange reactions offer a simple, non-vacuum route for adding Cu into In- Ga-Se precursor layers as a step in a low-cost process for the preparation of Cu(In, Ga)Se2 (CIGS) solar cells. The chemically treated precursor layers may be converted into CIGS by annealing with Se vapour. Structural and compositional characterisation has shown that the converted layers have good composition, microstructure and crystalline phase content. Nevertheless, photovoltaic cells processed from these layers have failed to produce energy conversion efficiencies greater than ~4% under standard test conditions. The chemical bath used for the incorporation of Cu into the precursor layers includes a complexant for stability and this complexant contains alkali atoms, which are known to strongly influence the properties of CIGS. Low alkali content is highly desirable in CIGS layers but excessive inclusion may be detrimental. This paper reports the results of an investigation into the potential incorporation of excess alkali atoms from the solution into the precursor layers. Whilst no evidence of alkali incorporation is detected by energy dispersive X-ray analysis, clear evidence is seen in time-of-flight secondary ion mass spectrometry measurements. The implications of this are discussed in terms of reported effects on device performance

Chemical incorporation of copper into indium selenide thin-films for processing of CuInSe2 solar cells

A chemical method of incorporating copper into indium selenide thin-films has been investigated, with the goal of creating a precursor structure for conversion into CuInSe2 layers suitable for solar cell processing. The precursor and converted layers have been investigated with scanning electron microscopy, x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy. From these measurements, the incorporation of copper into the indium selenide layers is concluded to proceed by an ion-exchange reaction. This reaction results in the formation of a precursor layer with a graded compositional depth-profile containing the crystalline phases In2Se3 and Cu2-xSe. Selenization of the precursor layer homogenises the composition and forms chalcopyrite CuInSe2. These CuInSe2 layers exhibit a dense microstructure with rough surface morphology, which is ascribed to a non-optimal selenization process. Solar cells with the structure ZnO:Al/i-ZnO/CdS/CuInSe2/Mo/Glass have been processed from the selenized layers and have exhibited efficiencies of up to 4% under simulated AM1.5 illumination

Incorporation of copper into indium gallium selenide layers from solution

A chemical method for the incorporation of copper into indium gallium selenide (IGS) layers has been developed. The resulting copper-containing precursor layers have been annealed in the presence of selenium vapour with the goal of forming Cu(In, Ga)Se2 (CIGS) layers. It is found that copper ions in solution are incorporated into IGS layers during immersion, resulting in the formation of a precursor layer containing both copper selenides and IGS. When aqueous solutions are used for this process, corrosion of the molybdenum back contact occurs by reduction of copper ions in the solution. Use of an ethylene glycol solution prevents corrosion of the Mo and allows higher process temperatures, corresponding to higher reaction rates. During annealing, the precursor layers are converted into CIGS and the morphology of these layers is strongly affected by the availability of selenium whilst the substrate temperature is ramped up