• Energy Research

AbstractIn this paper, we first give some historical background and trends in PV module technologies with a focus on the growing trend towards ‘PV everywhere’, mainly targeting improved aesthetics, dimensional freedom including curved surfaces, weight concerns and specific reliability testing. This section acts as an introductory review of the field.Then, in the following sections, we elaborate on two technological developments in this field where we are active: (i) multi‐wire interconnection and (ii) advanced encapsulation.In terms of multi‐wire interconnection, this technology offers improved aesthetics, a similar performance and dimensional freedom compared to the traditional tabbing‐stringing process, and the experiments show promising results on extended reliability testing, including thermal cycling, damp heat and humidity freeze, as well as high‐temperature storage.In terms of advanced encapsulation, we introduce our approach for curved surfaces using a double‐membrane laminator and present results on fabricating curved modules, targeting as demonstration examples on the one hand, glass–glass sunroofs, and on the other hand, lighter‐weight bonnets for automotive applications.We mix examples targeting building and automotive applications, to illustrate the variety of requirements (colours, curvature, weight, reliability, safety), although this variety within building and vehicle applications is probably as large as between them.

In the frame of the development of thin crystalline silicon solar cell technologies, surface nanopatterning of silicon is gaining importance. Its impact on the material quality is, however, not yet fully controlled.We investigate here the influence of surface nanotexturing on the series resistance of a contacting scheme relevant for thin-film crystalline silicon heterojunction solar cells. Two dimensional periodic nanotextures are fabricated using a combination of nanoimprint lithography and either dry or wet etching, while random pyramid texturing is used for benchmarking. We compare these texturing techniques in terms of their effect on the series resistance of a solar cell through a study of the sheet resistance (Rsh ) and contact resistance (Rc) of its front layers, i.e., a sputtered transparent conductive oxide and evaporated metal contacts. We have found by four-point probe and the transfer length methods that dry-etched nanopatterns render the highest Rsh and Rc values. Wet-etched nanopatterns, on the other hand, have less impact on Rc and render Rsh similar to that obtained from the nontextured case. Authors' post-print version in Abdo et al., IEEE Journal of Photovoltaics, July 2015

AbstractIn this paper, we investigate the mechanisms leading to rear reflectance losses in i-PERC type solar cells by means of reflectance measurements, scanning spreading resistance microscopy (SSRM), and transmission electron microscopy (TEM). Using 2μm sputtered (PVD) AlSi12.7% (eutectic composition) it is found that the interaction between Si present in the sputtered mixture and the rear dielectrics upon contact firing leads to a large drop in rear reflectance even without any laser ablated contact openings. On the other hand, in the case of local Al-BSF formation with pure PVD Al, it is shown that the presence of Si on top of the rear dielectrics, coming from Si diffusion into the Al layer with alloying, leads to parasitic absorption which contributes almost entirely to the measured drop in rear reflectance.

ABSTRACTDriven by the relatively high cost of silver (Ag), interest has grown in the photovoltaic (PV) industry to substitute conventional screen printed (SP) Ag front contacts with copper (Cu) plated contacts. The approach chosen here applies selective laser ablation of the front anti‐reflection coating (ARC), then forming self‐aligned nickel silicides (NiSix) contacts, and thickening the lines by Cu plating to achieve the desired line conductivity. A successful implementation of this scheme requires annealing to form NiSix with low contact resistance. However, it has been shown that industrial shallow emitters can be damaged severely upon conventional annealing of nickel. In this paper, we show that by using large area excimer laser annealing (ELA), NiSix contacts can be formed on industrial shallow emitters without the associated junction degradation. On the basis of sheet resistance, transmission electron microscopy, and lifetime measurements, we demonstrate that NiSix formation by ELA can be achieved in narrow contact openings without damaging the passivation and reflectance properties of the neighboring ARC. In addition, the thresholds for NiSix formation for different Ni thicknesses are quantified by rigorous finite element simulations and compared with experimental data. Finally, high efficiency passivated emitter and rear cell type solar cells featuring a shallow 85 Ω/sq emitter have been processed on large area CZ–Si using laser ablation of the ARC and subsequent NiSix formation by ELA. These cells show an average efficiency gain of 0.4%abs compared with cells processed with reference SP contacts. In this work, the best performing cell with the ELA process reached 20.0% energy conversion efficiency. Copyright © 2013 John Wiley & Sons, Ltd.

AbstractIn this work, we show the integration of polysilicon‐based passivating contacts in plated bifacial n‐type PERT (passivated emitter and rear totally diffused) solar cells. We show the viability of n‐PERT cells using two‐side passivating contacts with two‐side plated nickel/silver metallization. Compared with commercially available “TOPCon” cells with rear side passivated contacts only, n‐PERT cells with both side passivated contacts should enable the exploitation of the full potential of passivated contacts. We show that both n‐poly and p‐poly were applied and co‐plated successfully on both sides of n‐PERT solar cells. Considering the potential parasitic absorption losses on the front side of the device originating from p‐poly, we applied selective p‐poly by patterning. We compared two patterning methods for front side polysilicon: the masking and etch approach using inkjet printing and a simple and cost‐effective patterning method using UV laser oxidation. A best efficiency of 22.7% has been achieved with these cells so far on large area (244.3 cm2) n‐type Cz, with a potential efficiency above 24%. Some of these co‐plated bifacial cells have been processed into one‐cell laminates using smart wire interconnection (SWCT) technology. These have passed thermal cycling (TC) tests as defined in IEC61215.

AbstractNi/Cu plated front contacts are applied to large-area hybrid silicon heterojunction (SHJ) solar cells consisting of a diffused front surface field and intrinsic and boron doped a-Si:H(i/p+) layers forming the rear SHJ emitter. Nickel silicide front contacts are formed by excimer laser annealing (ELA) which unlike rapid thermal annealing (RTA) is shown to be compatible with a rear SHJ emitter. A top efficiency of 20.1% (externally confirmed at FhG-ISE CalLab), with jsc=39.0mA/cm2, Voc=675.1mV, and FF=76.5% is obtained on 15.6x15.6 cm2 n-type Cz-Si in a first trial and this without compromising solder tab adhesion results at the front side. Limitations arising from series resistance at the rear side and from recombination at the front side are discussed.

The integration of two-dimensional (2D) periodic nanopattern defined by nanoimprint lithography and dry etching into aluminum induced crystallization (AIC) based polycrystalline silicon (Poly-Si) thin film solar cells is investigated experimentally. Compared to the unpatterned cell an increase of 6% in the light absorption has been achieved thanks to the nanopattern which, in turn, increased the short circuit current from 20.6 mA/cm2 to 23.8 mA/cm2. The efficiency, on the other hand, has limitedly increased from 6.4% to 6.7%. We show using the transfer length method (TLM) that the surface topography modification caused by the nanopattern has increased the sheet resistance of the antireflection coating (ARC) layer as well as the contact resistance between the ARC layer and the emitter front contacts. This, in turn, resulted in increased series resistance of the nanopatterned cell which has translated into a decreased fill factor, explaining the limited increase in efficiency. Authors' post-print version