14%-efficient flexible CdTe solar cells on ultra-thin glass substrates
W. L. RanceJames M. BurstD. M. MeysingColin A. WoldenMatthew O. ReeseT. A. GessertWyatt K. MetzgerSean GarnerPat CimoTeresa M. Barnes
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Abstract:
Flexible glass enables high-temperature, roll-to-roll processing of superstrate devices with higher photocurrents than flexible polymer foils because of its higher optical transmission. Using flexible glass in our high-temperature CdTe process, we achieved a certified record conversion efficiency of 14.05% for a flexible CdTe solar cell. Little has been reported on the flexibility of CdTe devices, so we investigated the effects of three different static bending conditions on device performance. We observed a consistent trend of increased short-circuit current and fill factor, whereas the open-circuit voltage consistently dropped. The quantum efficiency under the same static bend condition showed no change in the response. After storage in a flexed state for 24 h, there was very little change in device efficiency relative to its unflexed state. This indicates that flexible glass is a suitable replacement for rigid glass substrates, and that CdTe solar cells can tolerate bending without a decrease in device performance.Keywords:
Cadmium telluride photovoltaics
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An ultra-thin Cadmium Sulphide (CdS)- Cadmium Telluride (CdTe) photovoltaic cell has been designed incorporating an intrinsic layer (i-CdTe) and p + -CdTe layer as a back surface field (BSF) to achieve high conversion efficiency. The optimized thickness of the proposed photovoltaic cell is only 1.9 μm. The conversion efficiency of the proposed cell increased noticeably with introducing a CdTe intrinsic layer. It is found that with the increase of thickness of intrinsic layer, the conversion efficiency increased. At a solar irradiance of AM 1.5, we achieved open circuit voltage (V oc ) of 0.93 V, short circuit current density (J sc ) of 47.52 mA/cm 2 , the maximum power of 36.91 mW/cm 2 and fill factor (FF) of 83.98%. The overall conversion efficiency of the proposed cell structure is achieved as 31%.
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In this study, the application and characteristics of photovoltaic cell fabricated with poly(3-hexylthiophene (P3HT) and its copolymers blending with (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) have been investigated. Studies on the enhancement for power conversion efficiency of photovoltaic cell for the influence of the annealing temperature, annealing time, and weight ratio of P3HT/PCBM have been carried out. To analysis the characteristics of the power conversion efficiency, studies on the energy band and the strength of absorption spectra have been investigated. The power conversion efficiency of the photovoltaic cell fabricatd with P3HT/PCBM (1:1) subjected to heat treatment at 150 ℃ for 15 or 20 min is about 0.42% ~ 0.46%, which are larger than that (0.08%) of the original device (without annealing). The characteristics of the photovoltaic cell fabricatd with P3HT/PCBM (1:0.8) subjected to heat treatment at 100, 150, 180, and 200 ℃ for 20 min have been invertigated. The short-circuit current density, open-circuit voltage, fill factor, and efficiency of device subjected to heat trement at 150 ℃ are 1.88 mA/cm2, 0.4 V, 0.46, and 0.86%, respectively. The short-circuit current density, open-circuit voltage, fill factor, and power conversion efficiency of the photovoltaic cell with P3HT/PCBM (of 3:1 weight ratio) subjected to heat treatment at 150 ℃ for 10 min are 4.3 mA/cm2, 0.35 ,and 1.12%, respectively. On the other hand, the short-circuit current density, open-circuit voltage, and power efficiency of the photovoltaic cell fabricated with copoly(3-hexylthiophene-co-3-dodecylthiophene (P3HTDDT), which is synthesized by our laboratory, blending with PCBM subjected to heat treatment at 150 ℃ for 15 min are 0.135 mA/cm2, 0.61 V, and 0.65%, respectively.
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The presence of a hole conducting agent in a quasi-solid state dye sensitized solar cell (DSSC) may improve cell parameters. The paper reports on the photovoltaic properties of two types of cells, one containing a layer of CuI on a dye coated ZnO electrode (cell A) and the other with CuI dispersed in a gel electrolyte (cell B). The cell A generated a short circuit current density of 7.45 mA·cm, an open-circuit voltage of 0.56 V, a fill factor of 0.54 and an overall power conversion efficiency of 2.26% under 100 mW·cm (air mass: 1.5). In cell B, an enhancement in its performance was observed. The cell showed 2.67% efficiency with a short circuit current density of 8.75 mA·cm, an open-circuit voltage of 0.59 V and a fill factor of 0.52. The increase in the performance is attributed to the improvement in the hole transport in the electrolyte. The efficiency of cell B was further increased to 3.38% by introducing a compact layer of ZnO 106 nm thick.
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An alternative model for glass/CG/CdS/CdTe/metal solar cell is presented. Using guidelines based on this new model, the authors have fabricated improved devices producing open-circuit voltage (V/sub oc/) values over 600 mV, fill factor (FF) values over 0.60 and the short-circuit current density (J/sub sc/) values over 60 mAcm/sup -2/ for best devices. Although V/sub oc/ and FF could be further improved, the remarkable improvement of J/sub sc/ indicates the possibility of further development of CdS/CdTe solar cell. Positive effects of n-type doping of CdTe with iodine and MlS type electrical contacts are presented.
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ABSTRACT Sputtered CdS/CdTe cells with only 0.75 µm of CdTe have reached AM1.5 efficiencies over 12.5%. But the use of very thin absorber layers of CdTe raises questions about the possible impact on long‐term stability when the back contact is very close to the main junction. In this study, we have performed accelerated life testing (ALT) on unencapsulated CdTe dot cells with absorber thickness ranging from 0.7 to 2.1 µm. After 900 h of ALT at 85°C under continuous one‐sun illumination, with open circuit biasing and no encapsulation, we find that any decrease in stability as CdTe thickness decreases is within the ~10% statistical uncertainty shown by the sample sets of more than 20 cells each. Cells of all thicknesses exhibited some decrease in performance under these stress conditions, and open‐circuit voltage appears to be the key factor in decreased efficiency. These changes in performance under ALT at 85°C are found to be consistent with a projected field lifetime of about 40 years in typical conditions. Secondary ion mass spectroscopy depth profiles of several elements including Cu showed no evidence of ALT‐driven diffusion in these sputtered CdTe cells. Copyright © 2013 John Wiley & Sons, Ltd.
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