Highly and Rapidly Stabilized Protocrystalline Silicon Multilayer Solar Cells
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A11.2.1
Highly and Rapidly Stabilized Protocrystalline Silicon Multilayer Solar Cells Koeng Su Lim, Joong Hwan Kwak, Seong Won Kwon, and Seung Yeop Myong Department of Electrical Engineering & Computer Science, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea ABSTRACT We have developed highly stabilized (p-i-n)-type protocrystalline silicon (pc-Si:H) multilayer solar cells. However, the source of the superior light-induced stability of the pc-Si:H multilayer absorbers compared to conventional amorphous silicon (a-Si:H) absorbers remains unclear. Photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy measured at room temperature produce strong evidence that nano-sized silicon grains embedded in regularly arranged highly H2-diluted sublayers suppress the photocreation of dangling bonds. To achieve a high conversion efficiency, we applied a double-layer p-type amorphous siliconcarbon alloy (p-a-Si1-xCx:H) structure to the pc-Si:H multilayer solar cells. The less pronounced initial short wavelength quantum efficiency variation as a function of bias voltage, and the wide overlap of dark current - voltage (JD-V) and short-circuit current - open-circuit voltage (Jsc-Voc) characteristics prove that the double p-a-Si1-xCx:H layer structure successfully reduces recombination at the p/i interface. Thus, we achieved a highly stabilized efficiency of 9.0 % without any back reflector. INTRODUCTION Thin film silicon solar cells employing amorphous silicon (a-Si:H) based absorbers have attracted great interest in the industrial realm due to their easy optical band gap design, lowtemperature, low-cost, and large-scale production. However, a-Si:H exhibits serious lightinduced degradation called the Staebler-Wronski effect [1]. The H2 dilution of SiH4 has attracted great interest in efforts to suppress the Staebler-Wronski effect in a-Si:H based material. Recently, so-called “edge” materials such as single layers of H2-diluted protocrystalline silicon (pc-Si:H) or nanocrystalline silicon (nc-Si:H) [2-6] were shown to be better absorbers than conventional H2-diluted a-Si:H due to their higher stability and vertical photosensitivity (the ratio of photo- to dark-conductivity). Because the former is fabricated just below the threshold of an amorphous-to-microcrystalline transition and the latter is fabricated just above the threshold of the transition, such depositions are very sensitive to the film thickness and H2 dilution. An a-Si:H/H2-diluted microcrystalline silicon (µc-Si:H) superlattice has been proposed as the most promising absorber due to its (i) isotropic transport properties achieved by perturbing the columnar growth of µc-Si:H [7] and (ii) lower sensitivity to the film thickness and H2 dilution than single layers of edge materials. However, this structure is unsuitable for mass production because of the discrete deposition of its sublayers. Therefore, we have developed pcSi:H multilayer absorbers that are prepared by alternate H2 dilution under continuous ultraviolet (UV) light irr
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