DAMP HEAT STABILITY OF TRANSPARENT CONDUCTIVE ZINC OXIDES: ROLE OF ENCAPSULANTS AND PROTECTIVE LAYERS

The mechanisms and environmental influences that cause photovoltaic modules performance degradation are poorly understood, but it is well known that water vapour is deeply implicated in the degradation process. Indeed, some layers and interfaces of thin film modules can be moisture sensitive and depending on the processing conditions, they degrade after exposure to damp heat conditions (85°C, 85% relative humidity) [1]. Transparent conductive oxides (TCO), as used in CIGS or thin silicon film cells play a particular role linked to reliability issues. We showed recently that low-pressure chemical vapour deposition zinc oxide (LPCVD ZnO) can withstand damp heat test even without encapsulant providing doping of the ZnO is high enough, though this is unfavourable for free carrier absorption (reduction of spectral response in the infrared part) [2]. Reduction of doping leads to improved optical properties but needs therefore an optimized encapsulation strategy to avoid the deterioration of the TCO conductivity. In previous work, the degradation of LPCVD ZnO used in thin-film silicon solar cells was investigated [3]. It was shown that the decrease of the ZnO conductivity was essentially due to the humidity increasing inside the encapsulant. However other effects take part in the degradation process and remained yet unexplained. In this paper we will report on several other possible sources of degradation, which have been identified. In order to demonstrate and quantify these effects, we used various encapsulants, but without back protection (foil or glass), and we exposed the samples to different type of atmospheres. The resistivity of the ZnO was monitored using an inductive contactless and a four points probe methods. Finally, schemes to perform highly reliable laminates when using lightly doped ZnO are proposed

Towards in-line determination of EVA Gel Content during PV modules Lamination Processes

Poly (ethylene-co-vinyl acetate) (EVA) is the major polymer used for photovoltaic (PV) modules encapsulation. Its degree of cross-linking (related to its gel content) is taken as a major quality reference. Differential Scanning Calorimetry (DSC) has been proven to be fast and effective but is to determine the gel content, however, destructive for the PV module. With the aim to develop a non-destructive quality assessment tool, a detailed discussion on the DSC thermogram of EVA PV encapsulant is presented here. A possible path towards a fast and non-destructive method for determing EVA gel content is proposed based on the DSC analysis

AN HYBRID LED/HALOGEN LARGE-AREA SOLAR SIMULATOR ALLOWING FOR VARIABLE SPECTRUM AND VARIABLE ILLUMINATION PULSE SHAPE

Commercial large-area solar simulators are principally in the form of Xenon flashers, which intrinsically have a short flash duration time, typically 100 ms at low spectrum quality and 10 ms at high spectrum quality. This implies measurement time constraints not adapted to the characterization of new generations of photovoltaic modules such as high-efficiency crystalline silicon modules, which can exhibit transient effects leading to measurement artifacts [1]. Moreover, thin film technologies require a high spectral match and possibly a variable spectrum of the illumination source for the accurate power-rating of multi-junctions based solar modules. An alternative large-area solar simulator solution is proposed for the power rating and the diagnostic of such generations of solar modules. The developed simulator makes use of a combination of different power LEDs and halogen lamps in a particular matrix configuration, integrated into a 1 m × 1 m table with mirrors. The constructed prototype demonstrates an AAA classification according to the IEC norms [2], allows for long illumination (200 ms to continuous) and permits controlled variation of the spectrum and of the intensity of the illumination