Insights into the reliability of Ni/Cu plated p-PERC silicon solar cells

Selective laser ablation of dielectric layers in combination with plated Ni/Cu/Ag contacts have been investigated by many photovoltaic researchers. Despite that there has been quite some practical progress on improved processing, the reliability of plated Ni/Cu/Ag cells still needs further insight and understanding. In this paper, the impact of laser induced defects that result from a ps-laser (wavelength 355nm) ablation on the performance of p-type PERC cells has been studied. A thermal stress experiment at 235 degrees C is applied. It is shown that the defects formed during the laser ablation process do indeed decrease the cell performance. A higher laser fluence results in lower fill factor and therefore lower efficiency. Moreover, the cells with higher laser fluence ablation degrade faster compared to the cells which had lower laser fluence to open the dielectric layer. The second part of the paper focuses on characterization of the p-n junction of the laser ablated cells by Deep Level Transient Spectroscopy (DLTS) before and after thermal ageing. A hole trap around 80K was found for all samples, which is related to point defects induced during the cell processing. A broad peak around 200K observed for the ablated cells with high laser fluence could correspond to dislocations induced by the laser ablation. This peak is shifted to higher energy (closer to the silicon mid-gap) after annealing, which may be due to impurity decoration during the annealing

Switched-capacitors as local converters for snake PV modules : a cost/efficiency exploration

In order to reduce the negative effect of partial shading and other sources of current mismatch within a module, smart reconfigurable modules allow altering the connections between groups of cells (cell-strings). With a proper algorithm managing these connections, we can make sure that the majority of the cells are operating close to their MPP, even when a part of the module is shaded. Such a smart reconfigurable module consists of some extra components. Switches are needed to change the interconnection scheme. Small, local converters collect power from multiple cell-strings. They step-up the voltage to reduce the current on the central bus they are connected to. At the end where we connect to the string-level bus, a module converter further regulates the voltage for the grid or the PV array. This topology was presented before where we showed that a smart reconfigurable module could recover up to 70% of the power lost to partial shading. In this paper we take a closer look at the local DC-DC converter. More precisely, we present a cost-efficiency analysis of different converter topologies. Taking into account practical limitations (economical limitations, number of components, maximum switch currents, maximum capacitance values, etc..) we estimate efficiency and projected cost. We show that Dickson pump (CR3) with 30-35mOhm switches is the best candidate. This would result in a chip cost of about €1.

Process Development of Silicon Heterojunction Interdigitated Back-Contacted (SHJ-IBC) Solar Cells Bonded to Glass

In imec’s i2-module concept, silicon heterojunction interdigitated back-contacted (SHJ-IBC) solar cells are fabricated on monocrystalline foils bonded to glass. The proposed technology allows for cell processing on thin wafers mechanically supported by the glass, increasing the yield of processing such thin wafers. A process sequence for SHJ-IBC cell fabrication that can be applied to bonded thin foils is described. We investigated and optimized individual process steps on thick wafers. Then the developed steps were integrated into a process flow to fabricate solar cells on wafers with different thicknesses and bonding agents. On wafers with a thickness of 190 μm, functional cells with efficiencies of 22.6% and 21.7% were made on freestanding and silicone bonded wafers, respectively. On thin wafers of 57 μm, our best SHJ-IBC cell on an EVA bonded wafer exhibits excellent Voc of 740 mV and efficiency of 20.0%, which demonstrates the high potential of the i2-module concept

How cool is floating PV? A state-of-the-art review of floating PV's potential gain and computational fluid dynamics modeling to find its root cause

The noticeable rise in electricity demand, environmental concerns, and the intense land burden has led to installing PV systems on water bodies to create floating photovoltaic (FPV). Of all market niches, FPV is the one developing the fastest. Along with some of its well-documented merits comes a claim that FPV modules operate at a lower temperature than their ground-mounted counterparts (GPVs). This claim is essential due to the performance loss of PV modules at high operating temperatures. Some literature claims that FPVs are so well-cooled that they maintain around 10% higher efficiencies. However, this cooling is poorly quantified, and the root cause remains unclear in the industry. In this paper, an extensive review of all the latest published literature and white paper advertisements was analyzed. The gains in energy yield coming from different root causes range from 0.11% to 31.29%! This proves the point of lack of clarity of potential gain of FPV. The paper then analyses four possible explanations for this cooling effect and its root causes. The FPV performance parameters are isolated and systematically investigated through physics-based finite element modeling. The impacts of wind velocity, wind direction, water temperature, relative humidity, air temperature, proximity to water, tilt angle, and others are evaluated and explained. The outcomes dictate that FPV is cooled largely through wind convection. But the increase in efficiency is below the anticipated values, ranging from 0.5% to 3%