Relationship between absorber layer defect density and performance of a‐Si:H and µc‐Si:H solar cells studied over a wide range of defect densities generated by 2 MeV electron bombardment
| Autor: | Bart E. Pieters, Friedhelm Finger, Vladimir Smirnov, Oleksandr Astakhov, Valeriy Borysenko, Yuri Petrusenko, Reinhard Carius |
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| Rok vydání: | 2014 |
| Předmět: |
Amorphous silicon
Materials science Silicon Renewable Energy Sustainability and the Environment business.industry Analytical chemistry chemistry.chemical_element Electron Surfaces Coatings and Films Electronic Optical and Magnetic Materials law.invention Amorphous solid chemistry.chemical_compound chemistry law Solar cell Optoelectronics Quantum efficiency business Electron paramagnetic resonance Order of magnitude |
| Zdroj: | Solar Energy Materials and Solar Cells. 129:17-31 |
| ISSN: | 0927-0248 |
| DOI: | 10.1016/j.solmat.2013.12.024 |
| Popis: | We summarize an extensive study on the impact of absorber layer defect density on the performance of amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon solar cells. To study the effects of the absorber layer defect density we subjected set of a-Si:H and μc-Si:H cells to a 2 MeV electron bombardment. Subsequently the cells were stepwise annealed to vary the defect density. The cells have varying thicknesses and are illuminated from either the p- or n-side. For reference we subjected i-layers to the same treatment as the cells. The procedure enabled the reversible increase of the i-layer defect density ( N S ) with two orders of magnitude according to electron spin resonance measurements (ESR) performed on reference samples. The large variation of N S induces substantial changes in the current–voltage characteristics ( J – V ) and the external quantum efficiency spectra (EQE). These changes in device characteristics provide a solid reference for analysis and device simulations. It was found that performance of a-Si:H cells degraded weakly upon N S increase up to 10 17 cm −3 and dropped steeply as defect density was increased further. In contrast, performance of µc-Si:H cells showed continuous reduction as N S raised. By comparing p- and n-side illuminated cells we found that, for N S above 10 17 cm −3 , the p-side illuminated a-Si:H cells outperformed the n-side illuminated ones, however, the difference was barely visible at N S below 10 17 cm −3 . On the contrary, the device performance of n-side illuminated µc-Si:H cells was much more affected by the increase in defect density, as compared to the p-side illuminated cells. EQE results evidenced a significant asymmetry in collection of electrons and holes in µc-Si:H devices, where carrier collection was limited by holes as defect density was increased. Based on the experimental data we speculate that the improvement of absorber material in terms of as-deposited defect density is not of primary importance for the performance of a-Si:H cells, whereas in μc-Si:H based solar cells, the reduction of the absorber layer defect density below the state-of-the-art levels, seems to improve the cell performance. |
| Databáze: | OpenAIRE |
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