Modeling of annealing kinetics for hydrogenated-amorphous-silicon-based solar cells using two-component metastable defects

Abstract

We propose a kinetic model for the annealing in p-i-n-type hydrogenated-amorphous-silicon ͑a-Si: H͒-based solar cells using a combination of the fill factor and "fast" and "slow" metastable defect states in their absorbers. Reported annealing data are simulated on p-i-n-type a-Si: H-based solar cells using the proposed model in order to confirm its validity. The recovery kinetic dependence on the thermal annealing temperature, biased voltage, and phase of the absorber controlled by the hydrogen dilution ratio during deposition are reviewed. Furthermore, we suggest a recovery mechanism for the solar cells based on long range hydrogen diffusion. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2213507͔Despite high interest of late in thin-film Si solar modules, a major obstacle to their commercialization remains. Specifically, light-induced degradation, which originates from the photocreation of dangling bonds ͑DBs͒ accomplished by the nonradiative recombination of photogenerated electron-hole pairs ͑Staebler-Wronski effect͒, 1 limits the efficiency of hydrogenated-amorphous-silicon ͑a-Si: H͒-based solar cells. In spite of extensive research on the StaeblerWronski effect during the past 30 years, there is no consensus on a microscopic mechanism that explains all experimental phenomena. Similarly, the recovery mechanism for a-Si: H-based solar cells through thermal annealing 2,3 or intense illumination at high temperature with a strong reverse bias 4 has yet to be identified: the recovery kinetics against thermal annealing is often interpreted by the stretched exponential kinetics 5,6 wherein defect generation and annealing for a-Si: H-based materials are controlled by only one type of metastable defect as a result of a dispersive process. 7 However, several recent studies have provided experimental evidence that a-Si: H-based materials possess "fast" and "slow" metastable defects, which is clearly contradictory to the stretched exponential kinetic model. [8][9][10] Thus, the stretched exponential kinetic model is no longer considered appropriate and the total defect density cannot uniquely determine the state for the a-Si: H-based solar cells. In the present work, a model of recovery kinetics for p-i-n-type a-Si: H-based solar cells employing the two-component metastable defect states is suggested.The fill factor ͑FF͒ was selected as a measure of the state for the a-Si: H-based solar cells due to the following reasons. ͑i͒ FF is sensitive to the quality of the intrinsic ͑i͒ absorber. ͑ii͒ Analytic equations relating FF to the collection length, i.e., FFϰ E, where and are the average mobility and lifetime of photogenerated carriers and E is the internal electric field in the i absorber, and to the defect density ͑or electron spin density͒ have been developed. 11 ͑iii͒ FF is the most degraded parameter against light soaking in a-Si: H-based solar cells 6,12 and is less sensitive to the measurement temperature and illumination intensity compared to the opencircuit voltage and short-circuit current. 2 FF for p-i-...

Modeling of amorphous InGaZnO4 thin film transistors and their subgap density of states

“…Amorphous semiconductors have been widely pursued for decades due to their wide applications and high uniformity. [1][2][3] Recently, amorphous oxide semiconductors ͑AOSs͒ have attracted much attention because AOS thin-film transistors ͑TFTs͒ exhibit large mobilities with lowtemperature or even room-temperature fabrication. [4][5][6][7][8][9] The conduction bands of the AOSs are derived from the ns orbitals of heavy metal cations such as In 3+ , Ga 3+ , and Zn 2+ .…”

Annealing Kinetic Model Using Fast and Slow Metastable Defects for Hydrogenated-Amorphous-Silicon-Based Solar Cells

“…In the previous report [15], the author proposed the following mechanism for the recovery kinetics in pin-type a-Si:H-based solar cells based on the TC model: (i) mobile H is thermally emitted from a metastable HSiDB defect by breaking the Si−H bond. As reflected in Figure 2, the elevated T A increases the thermal emission rate of mo-bile H [32]; (ii) emission of bonded H is followed by weak Si−Si bond reconstruction.…”

“…Yang and Chen suggested the existence of the fast and slow metastable defects in a-Si:H solar cells via twostep light soaking [11]; the cell subjected to an intense presoaking exhibits a thermal annealing behavior at the initial stage of 1-sun (AM 1.5, 100 mW/cm 2 ) post-soaking, which could be linked to annealing of the fast metastable defects. Since these results are clearly contradictory to the conventional SE kinetic model, the author suggested a new model of recovery kinetics for pin-type a-Si:H-based solar cells employing the two-component (TC) metastable defect states [15]. We selected the fill factor (FF) as a measure of the state for the a-Si:H-based solar cells due to the following reasons: (i) FF is sensitive to the quality of the intrinsic absorber (iabsorber); (ii) analytic equations relating FF to the collection length and to the defect density (or electron spin density) have been developed [16,17]; and (iii) FF is the most degraded parameter against light-soaking in a-Si:H-based solar cells [18] and is less sensitive to the measurement temperature and illumination intensity compared to the open-circuit voltage and short-circuit current [4].…”

Recent Progress in Inorganic Solar Cells Using Quantum Structures

“…Thus, some photoexcited carriers generated in the a-Si:H matrix of all sublayers can diffuse to grainboundary regions surrounding nc-Si grains. Several recent reports have suggested "fast" and "slow" metastable defects in the a-Si:H matrix [72][73][74]. From the fast metastability and annealing behaviors of pc-Si:H multilayer solar cells, the vertically regular distribution of the isolated nc-Si grains and the improved medium-range-order in the a-Si:H matrix are considered to localize the photocreation near the grain boundary regions, and thereby suppress photocreations of slow metastable defects in the pc-Si:H multilayer.…”