Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films.

1] Laboratory for Thin Films and Photovoltaics, Swiss Federal Laboratories for Materials Science and Technology Empa, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland [2].
Nature Material (Impact Factor: 35.75). 09/2011; 10(11):857-61. DOI: 10.1038/nmat3122
Source: PubMed

ABSTRACT Solar cells based on polycrystalline Cu(In,Ga)Se(2) absorber layers have yielded the highest conversion efficiency among all thin-film technologies, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Aims: Today's cardiac pacemakers are powered by batteries with limited energy capacity. As the battery's lifetime ends, the pacemaker needs to be replaced. This surgical re-intervention is costly and bears the risk of complications. Thus, a pacemaker without primary batteries is desirable. The goal of this study was to test whether transcutaneous solar light could power a pacemaker. Methods and results: We used a three-step approach to investigate the feasibility of sunlight-powered cardiac pacing. First, the harvestable power was estimated. Theoretically, a subcutaneously implanted 1 cm2 solar module may harvest ∼2500 µW from sunlight (3 mm implantation depth). Secondly, ex vivo measurements were performed with solar cells placed under pig skin flaps exposed to a solar simulator and real sunlight. Ex vivo measurements under real sunlight resulted in a median output power of 4941 µW/cm2 [interquartile range (IQR) 3767–5598 µW/cm2, median skin flap thickness 3.0 mm (IQR 2.7–3.3 mm)]. The output power strongly depended on implantation depth (ρSpearman = −0.86, P < 0.001). Finally, a batteryless single-chamber pacemaker powered by a 3.24 cm2 solar module was implanted in vivo in a pig to measure output power and to pace. In vivo measurements showed a median output power of >3500 µW/cm2 (skin flap thickness 2.8–3.84 mm). Successful batteryless VVI pacing using a subcutaneously implanted solar module was performed. Conclusion: Based on our results, we estimate that a few minutes of direct sunlight (irradiating an implanted solar module) allow powering a pacemaker for 24 h using a suitable energy storage. Thus, powering a pacemaker by sunlight is feasible and may be an alternative energy supply for tomorrow's pacemakers.
    Europace 01/2014; · 2.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Until this day, the most efficient Cu(In,Ga)Se2 thin film solar cells have been prepared using a rather complex growth process often referred to as three-stage or multistage. This family of processes is mainly characterized by a first step deposited with only In, Ga and Se flux to form a first layer. Cu is added in a second step until the film becomes slightly Cu-rich, where-after the film is converted to its final Cu-poor composition by a third stage, again with no or very little addition of Cu. In this paper, a comparison between solar cells prepared with the three-stage process and a one-stage/in-line process with the same composition, thickness, and solar cell stack is made. The one-stage process is easier to be used in an industrial scale and do not have Cu-rich transitions. The samples were analyzed using glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction, current–voltage-temperature, capacitance-voltage, external quantum efficiency, transmission/reflection, and photoluminescence. It was concluded that in spite of differences in the texturing, morphology and Ga gradient, the electrical performance of the two types of samples is quite similar as demonstrated by the similar J–V behavior, quantum spectral response, and the estimated recombination losses. Copyright © 2014 John Wiley & Sons, Ltd.
    Progress in Photovoltaics Research and Applications 01/2014; · 7.71 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An all-solid-state, lightweight, flexible, and wearable polymer solar cell (PSC) textile with reasonable photovoltaic performance has been developed. A metal textile electrode made from micrometer-sized metal wires is used as the cathode, and the surfaces of the metal wires are dip-coated with the photoactive layers. Two ultrathin, transparent, and aligned carbon nanotube sheets that exhibit remarkable electronic and mechanical properties were coated onto the modified metal textile at both sides as the anode to produce the desired PSC textile. Because of the designed sandwich structure, the PSC textile displays the same energy conversion efficiencies regardless of which side it is irradiated from. As expected, the PSC textiles are highly flexible, and their energy conversion efficiencies varied by less than 3 % after bending for more than 200 cycles. The PSC textile shows an areal density (5.9 mg cm−2) that is lower than that of flexible film-based PSCs (31.3 mg cm−2).
    Angewandte Chemie 08/2014;

Full-text (2 Sources)

Available from
Oct 16, 2014