2012, Article / Letter to editor (Journal of Non-Crystalline Solids, vol. 17, iss. 358, (2012), pp. 2308-2312)We present a novel method to achieve light trapping in thin film silicon solar cells. Unlike the commonly used surface textures, such as Asahi U-type TCO, that rely on light scattering phenomena, we employ embossed periodically arranged micro-pyramidal structures with feature sizes much larger than the wavelength of visible light. Angular resolved transmission of light through these substrates indeed showed diffraction patterns, unlike in the case of Asahi U-type substrates, which show angular resolved scattering. Single junction amorphous silicon (a-Si) solar cells made at 125 °C on the embossed structured polycarbonate (PC) substrates showed an increase in current density by 24% compared to a similar solar cell on a flat substrate. The band gap and thickness of the i-layer made by VHF PECVD are 1.9 eV and 270 nm respectively. A double p-layer (nc-Si:H/a-Si:H) was used to make proper contact with ZnO:Al TCO. Numerical modeling, called DokterDEP was performed to fit the dark and light current–voltage parameters and understand the characteristics of the cell. The output parameters from the modeling suggest that the cells have excellent built-in potential (Vbi). However, a rather high recombination voltage, Vµ, affects the FF and short circuit current density (Jsc) for the cells on Asahi as well as for the cells on PC. A rather high parallel resistance » 1 MO cm2 (obtained from the modeling) infers that there is no significant shunt leakage, which is often observed for solar cells made at low temperatures on rough substrates. An efficiency of more than 6% for a cell on PC shows enormous potential of this type of light trapping structures.
2012, Article / Letter to editor (Progress in Photovoltaics: Research and Applications, (2012))In this study, we present a new light absorption enhancement method for p-i-n thin film silicon solar cells using pyramidal surface structures, larger than the wavelength of visible light. Calculations show a maximum possible current enhancement of 45% compared with cells on a flat substrate. We deposited amorphous silicon (a-Si) thin film solar cells directly onto periodically pyramidal-structured polycarbonate (PC) substrates, which show a significant increase (30%) in short-circuit current over reference cells deposited on flat glass substrates. The current of the cells on our pyramidal structures on PC is only slightly lower than that of cells on Asahi U-type TCO glass (Asahi Glass Co., Tokyo, Japan), but suffer from a somewhat lower open circuit voltage and fill factor. Because the used substrates have a locally flat surface area due to the fabrication process, we believe that the current enhancement in the cells on structured PC can be increased using larger or more closely spaced pyramids, which can have a smaller flat surface area.
2011, Article / Letter to editor (Work and Stress, vol. 25, iss. 4, (2011), pp. 338-354)There is an increasing need for managers to understand what motivates younger versus older workers to continue work within their company. We believe that this two-wave study among 90 Dutch employees is the first to examine: (1) the cross-lagged relationships between breach of psychological contract (which includes transactional and relational obligations) and intrinsic work motivation, and (2) the moderating role of the age-related variables future time perspective and regulatory focus. Regulatory focus concerns the orientation (either promotion-focused or prevention-focused) by which an individual pursues their goals. Based on psychological contract theory, we expected and found that relational contract breach predicts lower work motivation. Furthermore, based on lifespan developmental and regulatory focus theory, we assumed that this relationship would be stronger when workers experienced an open future time perspective and a promotion focus rather than a prevention focus. The results showed that future time perspective indeed had a strengthening, and prevention focus a reducing moderating effect in the relationship between psychological contract breach and work motivation. However, no significant effects for promotion focus were found. These findings indicate that age-related processes such as future time perspective and regulatory focus are important variables to include in future psychological contract research.
2010, Article / Letter to editor (Tijdschrift voor Gezondheidswetenschappen, (2010))Dit artikel bespreekt enkele ontwikkelingen in het veld van gezondheidsbevordering en de implicaties hiervan voor de professionalisering van de gezondheidsbevorderaars.