论文英文翻译

1、.Temperature Dependence of Si-Based Thin-Film Solar Cells Fabricated on Amorphous to Microcrystalline Silicon Transition PhaseKobsak SRIPRAPHA Ihsanul Afdi YUNAZ Seung Yeop MYONG Akira YAMADA and Makoto KONAGAIDepartment of Physical Electronics, Tokyo Institute of Technology, 2-12-1-S9-9, O-okayama,

2、 Meguro-ku, Tokyo 152-8552, Japan Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1-S9-9, O-okayama, Meguro-ku, Tokyo 152-8552, Japan(Received June 5, 2007; accepted August 20, 2007; published online November 6, 2007)The temperature dependence of silicon (Si)-based thin-

3、film single-junction solar cells, whose intrinsic absorbers were fabricated on the transition phase between hydrogenated amorphous silicon (a-Si:H) to hydrogenated microcrystalline silicon (mc-Si:H), was investigated. By varying the hydrogen dilution ratio, wide-band-gap protocrystalline silicon (pc

4、-Si:H) and mc-Si:H absorber layers were obtained. Photo-current densityvoltage (Photo-JV) characteristics were measured under AM1.5 illumination at ambient temperatures in the range of 25 75 C. We found that the solar cells with pc-Si:H, which exists just below the a-Si:H to mc-Si:H transition bound

5、ary, showed the lowest temperature coefficient (TC) for conversion efficiency and open-circuit voltage (Voc), while the solar cells fabricated at the onset of the a-Si:H to mc-Si:H phase transition exhibited a relatively high TC for and Voc. Experimental results indicated that pc-Si:H is a promising

6、 material for the absorber layer of the single junction or the top cell of tandem solar cells that operate in high temperature regions.KEYWORDS: temperature dependence, amorphous silicon, protocrystalline silicon, Si thin-film solar cell, solar cells 1. Introduction In general, the solar cell perfor

7、mance is measured under the standard test conditions (STC) of a cell temperature of 25 摄氏度and an irradiance of 100mWcm2 with AM 1.5 spectral distributions. However, in an outdoor installation, the operating temperature of solar cells considerably changes depending on the environment, i.e., the clima

8、te in the installed area.In a tropical region, the operating temperature often reaches more than 70 摄氏度. The increase in the operating temperature leads to a decline in conversion efficiency mainly due to the drop in open-circuit voltage(Voc) Among Si-based solar cells, bulk crystalline Sisolar cell

9、s which include single-crystalline-Si (c-Si) and polycrystalline-Si (poly-Si) solar cells show higher than thin-film solar cells at room temperature. However, of c-Siand poly-Si solar cells seriously decreases with an increase in the operating temperature, while hydrogenated amorphous Si (a-Si:H)-ba

10、sed thin-film solar cells exhibit relatively small variation in. The main reason for the lowertemperature coefficient (TC) of a-Si:H-based solar cells is their wide-band-gap intrinsic absorber or high Voc compared with those of bulk crystalline Si-solar cells. Taking the real output power affected b

11、y the operating temperature and production cost into account, a-Si:H-based thin-film solar cells have advantages over bulk crystalline-Si solar cells for use in high temperature areas such as a tropical region. However, it is well known that a-Si:H-based thin-film solar cells exhibit light-induced d

12、egradation after light exposure, the so-called StaeblerWronski effect (SWE).The SWE in a-Si-based thin-film solar cells is also a veryim portant factor that must be considered for outdoor installation. During the past 30 years, extensive research has been conducted to suppress the SWE. As a result,

13、two kinds of edge materials near the phase boundary have been developed as stable intrinsic absorbers: one is the wideband- gap protocrystalline silicon (pc-Si:H) existing just below the a-Si:H-to-microcrystalline silicon (mc-Si:H) transition transition and the other is the narrow-band-gap mc-Si:H w

14、ith crystalline silicon volume fraction (Xc) of 30 50% obtained near the onset of the phase transition. The pc-Si:H material nucleate from the deposition of the a-Si:H at just before the transition boundary of a-Si:H to a-Si:H t mc-Si:H mixedphase. Once, the a-Si:H t mc-Si:H transition is detected,w

15、hich can be observed by a real time spectroscopic ellipsometry (RTSE), the growing material is no longer considered pc-Si:H.10) The unique properties of pc-Si:H are the optical band gaps (Eopt) and the Urbach tail. The Eopt of pc-Si:H is larger than conventional material and increases with increasin

16、g H2 dilution ratio. Besides, the narrower Urbach tail in pc-Si:H causes the higher hole drift mobility than conventional materials. The key feature of the pc-Si:Hmaterial is its relative stability to light induced degradation as observed in the electron-mobility lifetime product and similarly in th

17、e solar cell fill factor. These two kinds of materials are attractive for application to Si-based thin-filmsolar cells because of their low SWE. Although the pc-Si:H solar cell has shown a good temperature dependence among Si-based thin-film solar cells, the behavior of TC for pc-Si:H solar cells ha

18、s not yet been clarified. In this work, we investigated the temperature dependence of a-Si:H-based solar cells fabricated in the pc-Si:H to mc-Si:H transition regime. The TC values after lightinduced degradation were also investigated in order to findthe optimal absorber layer for the use at high op

19、erating temperatures.2. Experimental Procedure The pin single-junction solar cells were fabricated on Asahi U-type glass substrates in a multi chamber system with the structure of glass/SnO2:F/hydrogenated p-type amorphous silicon carbide (p-a-SiC:H)/buffer/intrinsic (i-)absorber/n-type amorphous si

20、licon (n-a-Si:H)/boron-doped zinc oxide (ZnO:B)/Ag/Al with the cell area of 0.086 cm2.The thicknesses of p, buffer, i-, and n-layers were kept constant at around 12, 4, 320 340, and 2 nm, respectively.All solar cells were fabricated at the substrate temperature of around 200 C with deposition pressu

21、res of 50 70 Pa. Thevery high frequency (60 MHz) plasma-enhanced chemical vapor deposition (VHF-PECVD) was used to deposit the i-layer. The i-layers were deposited at different silane concentrations, SC ?SiH4=eSiH4 t H2T, by varying SC from 6.0 to 2.4% in order to obtain material with the phase tran

22、sition from amorphous to microcrystalline silicon.With a decrease in SC, the deposition rate of the i-layerdeclined from 1.6 to 0.9. The doped (p- and n-layers) and buffer layers were deposited by a radio-frequency(13.56MHz) PECVD technique. ZnO was deposited by metal organic chemical vapor depositi

23、on (MOCVD) as a back reflector, while Ag and Al were evaporated as back electrodes for all samples.The Raman spectroscopy was performed using a JASCONRS-1000 system with a semiconductor laser at a wavelength of 532 nm. Ex-situ spectroscopic ellipsometry (SE)measurements (J. A. Wollam) were used with

24、 a variableangle spectroscopic ellipsometer. The temperature dependence of the solar cell parameters were measured using a solar simulator in a chamber at ambient temperatures (T) in the range of 25 75 C with a step increment of 10 C under 1-sun (AM1.5, 100mWcm2) irradiation. The temperature of the

25、sample was regulated by a temperature-controlled airflow. The temperature dependence of solar cells was obtained from photo-current densityvoltage (photo-JV) measurements. The value of TC can be expressed as where Z denotes the solar cell parameters, i.e., Voc, shortcircuit current density (Jsc), an

26、d fill factor (FF). The normalized temperature Tn is chosen to be 25 C because it corresponds to the standard reference condition for solar cell measurement. The 1-sun standard light-soaking test was performed in a climate chamber at the temperature of 50 C for 100 h.3. Results and Discussion3.1 Cha

27、racterization of intrinsic absorbersIn the first series of experiments, we inspected the Raman spectra for the solar cells fabricated in the phase transition regime. Figure 1 shows the Raman spectra for solar cells prepared with different SCs which are measured from the nside(rear-side of the solar

28、cells). The Raman spectra were deconvoluted to four Gaussian peaks centered at the Raman shift areas at around 430, 480, 510, and 520 cm1, whichcorrespond to the longtitude optical (LO) mode of a-Si:H, the transverse optical (TO) mode of a-Si:H, the defective crystalline phase and the TO mode of c-S

29、i, respectively. The defective part of the crystalline phase is included in thecrystalline fraction.15) The Xc calculated from the Raman spectrum is expressed as where Ii is the area under the Gaussian peak centered at the Raman shift of i cm1 and I480 t I510 t I520 is the total integrated area. By

30、decreasing SC from 6.0 to 4.0%, the peak position of Raman spectra of a-Si:H in the TO mode increased from the Raman shift of 475 to 480 cm1, as shown by the solid line in the figure, which means that the a-Si:Hmicrostructure improved when SC decreased, leading to further improvement of stability ag

31、ainst illumination.16) For SC ?3:2%, the Raman spectra exhibited two peaks at 480 and 517 cm1, which correspond to the onset of mc-Si:H growth. With further decrease of SC, SC 3:2%) to the onset of mc-Si:H solar cells (SC ?3:2%), Voc and FF both decreased and drastically fellwhen the films approache

32、d the mc-Si:H region (SC 3:2%),resulting in the consecutive decline in the . The highest initial of 9.44% was obtained from a solar cell fabricated at SC of 6.0%. It was also found that Jsc and FF were less sensitive to T than Voc. The temperature dependence of solar cell parameters is shown in Tabl

33、e I. Figure 3 shows the normalized solar cell parameters in the initial state. In general, FF of a Si-based solar cell decreases when T becomes high, mainly because of the reduction of Voc. However, it has been reported that for a-Si:H-based thin-film solar cells, FF sometimes increases with increas

34、ing T. This is probably due to the decrease of the contact resistance or the increase of the mobility-carrier lifetime product within the collection regionin a-Si:H solar cells. It was concluded that the increase incollection length with T was large in a-Si:H solar cells with poor transport properties. As shown in Fig. 3, normalized Voc for the pc-Si:H solar cell (SC between 6.0 and 4.0%) exhibited less degradation with the increase of temperature. Voc also drastically fell when SC reached 2.4%, because of the strong influence of t