A concept for Lithography-free patterning of silicon heterojunction back-contacted solar cells by laser processing

Silicon heterojunction (SHJ) solar cells with an interdigitated back-contact (IBC) exhibit high conversion efficiencies of up to 25.6%. However, due to the sophisticated back-side pattern of the doped layers and electrode structure many processing and patterning steps are required. A simplification of the patterning steps could ideally increase the yield and/or lower the production costs. We propose a patterning approach for IBC SHJ solar cells free of any photo-lithography with the help of laser-induced forward transfer (LIFT) of the individual layer stacks to create the required back-contact pattern. The concept has the potential to lower the number of processing steps significantly while at the same time giving a large degree of freedom in the processing conditions optimization of emitter and BSF since deposition of the intrinsic/doped layers and processing of the wafer are all independent from each other.Comment: 6 pages, 3 figures, 1 tabl

Vehicular Visible Light Communications

Vehicular communications are foreseen to play a key role to increase road safety and realize autonomous driving. In addition to the radio frequency (RF)-based dedicated short range communication (DSRC) and long-term evolution (LTE) communication technologies, vehicular visible light communication (V2LC) is proposed as a complementary solution, utilizing readily deployed vehicle light emitting diode (LED) lights as transmitter with image sensors such as photodetector (PD) and camera as the receivers. V2LC fundamentals including transmitter and receiver characteristics with dimming capabilities are reviewed in this chapter. Depending on the field measurements using off-the-shelf automotive LED light, communication constraints are demonstrated. Moreover, considering the line-of-sight (LoS) characteristics, security aspects of V2LC is compared with the DSRC for a practical vehicle-to-vehicle (V2V) communication scenario. Finally, superiority of V2LC in terms of communication security with the proposed SecVLC method is demonstrated through simulation results

Flexible design of building integrated thin‐film photovoltaics

The high cost of building integrated photovoltaics is one of the main reasons preventing a more widespread application. We propose a panel-on-demand concept for flexible design of building integrated thin-film photovoltaics to address this issue. The concept is based on the use of semi-finished PV modules (standard mass products) with subsequent refinement into BIPV PV modules. In this study, we demonstrate the three processes necessary to realize this concept. First, a prototype tool to cut thin film photovoltaic elements on glass substrates based on laser perforation was developed. Damage to the processed samples did not exceed a distance of 50 μm from laser cuts. Second, oxide/metal/oxide-electrodes with integrated colour were applied on Cu (In, Ga)Se2 cells and standard monolithic interconnection structuring was used to produce modules sized 30 × 30 cm2 in red, green and blue with strong colours. Third, A back-end interconnection process was developed for amorphous silicon thin film cells, which allows for the structuring of modules from elements of custom shape. The panel-on-demand strategy may allow for a streamlined production of customized modules and a lower cost for aesthetically pleasing, fully building integrated solar modules

Laser processing for the integrated series connection of thin-film silicon solar cells

The integrated series connection of solar cells is an essential aspect for thin-film photovoltaic technology. With a series connection a high output voltage of the module is achieved while the output current is kept low. Thus, Ohmic losses in the contact materials are kept low as well. In thin-film silicon solar technology the steps to create the interconnection are commonly done by laser ablation integrated in-between the depositions of the solar cell layer materials. In three steps laser scribing is used to selectively remove layers locally in the form of lines across the module substrate. In a first step the front-contact is removed for electrical insulation and cell stripe definition. Afterwards, the absorber is removed locally exposing the front-contact beneath. Finally, the interconnection is formed when the back-contact is removed locally as well. The area that is needed for the interconnection of two neighboring cells is no longer active for current generation. Depending on the technology 5-10% of active area is lost. The reduction of this area holds an attractive potential for an increase of the module efficiency. The topic of this thesis is the investigation of the lower geometrical limits for the dead area reduction for substrate side laser processing of thin-film silicon solar cells. It is well-known that the interconnection and the laser processes can have an impact on the performance of the solar module. Therefore, the characterization of the impact on the performance is of special importance when laser processes are used that are capable of generating a reduced interconnection width. P1: for the front-contact insulation process it was found out that the scribe quality strongly depends on the used laser wavelength. Ablation mechanisms that are driven by material phase changes (scribing with 532nm or 1064nm) can lead to smoother scribe edges compared to mechanisms dominated by stress-induced removal (355nm) where non-uniform rip-off at the edges occurs. However, in certain processing regimes, strong ablation debris redeposition in direct vicinity of the P1 scribe is observed when small beam spot radii (<10µm) are used. Such redeposition has a severe impact on the solar cell performance in this region. With proper wet-chemical cleaning the amount of redeposited debris on the front-contact and the negative impact on the solar module can be minimized. Parasitic shunting of two neighboring cell stripes by deposition of absorber material into the P1 scribe increases when the scribe width is reduced. Measurements show that the overall magnitude of the shunt is in a value range that impact on the solar module is negligible for commonly used cell topologies. P2: the width reduction approach was extended for the absorber removal process (P2). To ensure the selectivity of silicon removal without damaging of the front-contact beneath, only 532nm was used for scribing. For this wavelength ablation is strongly assisted by mechanical stresses generated by hydrogen diffusion from the absorber layer and/or thermal expansion of the absorber layer. Mechanical constraints limiting the lower scribe width are found that depend on the absorber thickness and the laser beam spot size. Such behavior can be explained directly from linear elastic fracture mechanics where removal of the layer is determined by the relation between delamination at the interface and fracture of the absorber along the circumference of the spot. It can be concluded that for substrate side laser-induced ablation thin scribe lines are only possible for thin layers. The parasitic series resistance formed by P2 also increases as the scribe width is decreased. However, for processing of amorphous silicon absorbers, with a beam radius 10µm, the minimal achievable resistance value is strongly increased. In fact, much more than what would be expected just by the geometrical contact area reduction. This is most likely owed to changes of the specific contact resistance due to increased debris redeposition within the P2 scribe prior to back-contact deposition. In contrast, such effects are not observed for processing of tandem absorber where debris redeposition is less pronounced. Here, low series resistances, with only minor impact on the module performance, are achieved for all investigated beam spot sizes. P3: the back-contact insulation process (P3) is similar to P2 since the back-contact is removed indirectly by removal of the absorber beneath. Shunting between front- and back-contact can occur at the direct P3 scribe edges. These shunts are possibly formed due to heat generated by sub-threshold energy intake of excess energy from the shoulders of Gaussian distribution of the laser. The mechanical constraints on the minimal achievable scribe widths are even stronger than what was observed for the optimization of the P2 process. This is owed to the additional overall thickness of the layer-stack due to the back-contact. Furthermore, for tandem solar cell processing the scribe edges are strongly distorted by delaminated material while clean edges are obtained for a-Si:H solar cells. The parasitic shunting by P3 scribing increases by many orders of magnitude when a processing beam radius of 10µm is used. However, just like it was observed from P2, an overall weaker deterioration is obtained for scribing of tandem solar cells than for amorphous silicon cells. It is possible that material modifications are more localized in the a-Si:H top-cell. Together with the higher thickness of the tandem cells (300nm vs. 1.4µm) the impact on the whole device is not as pronounced

Investigating the effects of maintenance and environmental conditions on the operational efficiency of ships by analysis on the real operational data

The maritime sector has recently been under pressure to reduce its fuel consumption due to the restriction on Greenhouse gas emissions and fuel prices. The new regulations of the International Maritime Organisation (IMO) regarding operational management and design limitations enter force in following years. Besides that, fuel consumption cost represents a major of total ship operation cost. Due to these, environmental performance and energy efficiency are top issues for ship operators and technical departments who are in pursue of cost reductions and greener operations. In this case, fouling management by hull and propeller cleaning and intelligent operations by considering environmental conditions may give ship operators to reach remarkable fuel saving. In this study, different 7 ships' noon data are examined in terms of fouling and environmental conditions such as sea state and sea direction. The Energy Efficiency Operation Indicator (EEOI) and main engine fuel consumption per nautical miles (T/NM) are considered as efficiency Key Performance Indicators (KPIs). This research's aim is to analyse of fuel consumption data before and after hull and propeller cleaning period and indicate any relevant way of these maintenances affects fuel consumption. Secondly, this research also aims to determine how ship speed is influenced by different sea state conditions and different wave & wind directions.The maritime sector has recently been under pressure to reduce its fuel consumption due to the restriction on Greenhouse gas emissions and fuel prices. The new regulations of the International Maritime Organisation (IMO) regarding operational management and design limitations enter force in following years. Besides that, fuel consumption cost represents a major of total ship operation cost. Due to these, environmental performance and energy efficiency are top issues for ship operators and technical departments who are in pursue of cost reductions and greener operations. In this case, fouling management by hull and propeller cleaning and intelligent operations by considering environmental conditions may give ship operators to reach remarkable fuel saving. In this study, different 7 ships' noon data are examined in terms of fouling and environmental conditions such as sea state and sea direction. The Energy Efficiency Operation Indicator (EEOI) and main engine fuel consumption per nautical miles (T/NM) are considered as efficiency Key Performance Indicators (KPIs). This research's aim is to analyse of fuel consumption data before and after hull and propeller cleaning period and indicate any relevant way of these maintenances affects fuel consumption. Secondly, this research also aims to determine how ship speed is influenced by different sea state conditions and different wave & wind directions