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| Die eta-Solarzelle: Ein neues Solarzellenkonzept mit extrem dünnem Absorber auf der Basis einer strukturierten TiO2/CdTe-Grenzfläche Ernst, Katja |
| Main title | Die eta-Solarzelle: Ein neues Solarzellenkonzept mit extrem dünnem Absorber auf der Basis einer strukturierten TiO2/CdTe-Grenzfläche |
| Title variations | The eta-solar cell: a new solar cell concept with extremely thin absorber based on a structured TiO2/CdTe-junction |
| Author(s) | Ernst, Katja
Place of birth: Kirchhellen Deutschland |
| 1. Referee | Prof. Martha-Christina Lux-Steiner |
| Further Referee(s) | Prof. Hans-Joachim Lewerenz |
| Keywords | eta-solar cell, CdTe, porous TiO2, electrical transport84.60Jt |
| Classification (DDC) | 530 Physics |
| Summary | The concept of a solar cell with an extremely thin absorber (eta) is based on the reduction of transport distances in a solar cell in order to use absorber materials of low electronic quality, i.e. small diffusion lengths. This work presents for the first time an eta-solar cell consisting of a structured pn-heterojunction between a n-type window material and a p-type absorber. The local absorber thickness that determines the maximum transport path is around 150nm. The thesis comprises the screening of different materials such as TiO2, ZnO and ZnTe and different morphologies regarding scattering properties, surface enlargement, structure and absorption behavior. For the solar cell microporous TiO2 has been used as a substrate combined with CdTe as absorber material. The conformal coverage of the structured TiO2-substrates prepared by spraypyrolysis has been achieved by electrodeposition of CdTe. After a post-deposition treatment of the CdTe in CdCl2-environment, which leads to a recrystallization of the material, the TiO2 is covered by small crystallites with a size in the order of the local absorber thickness, so that the light generated minority charge carriers do not have to pass any grain boundaries inside the CdTe for collection. The solar cell shows an open circuit voltage of Voc=680mV and a short circuit current of jsc=8.9mA/cm2. The eta-solar cell is compared to a planar configuration of the same materials: it is shown that the photocurrent is increased drastically when using an eta-configuration. The reason can be found in a low minority carrier diffusion length in the electrodeposited CdTe. In an eta-solar cell the space charge region penetrates most of the CdTe-layer, so that despite of the short diffusion length efficient collection of the photogenerated charge carriers can be achieved. The optical comparison via simulating transmission- and reflection-data shows a possible enhancement of the absorption in the CdTe of about a factor of 6 particularly for very thin CdTe-layers due to multiple scattering processes. A detailed analysis of the TiO2/CdTe interface by XPS and UPS reveals a valence band offset of 2.5eV leading to a conduction band offset of 0.6eV between TiO2 and CdTe. The conduction band offset leads to a diminished electric field inside the CdTe-absorber and, in combination with a short diffusion length of minority charge carriers, to a strong voltage dependent photocurrent collection. The resulting low fill factor of the solar cell turns out to be the limiting factor for the efficiency of this new solar cell concept at the moment. |
| Documents |
FUDISS_derivate_000000000406
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| FU Department | Department of Physics |
| Year of publication | 2001 |
| Document type | Doctoral thesis |
| Media type/Format | Text |
| Language | German |
| Terms of use/Rights | Nutzungsbedingungen |
| Date of defense | 2001-05-09 |
| Created at | 2001-06-26 : 12:00:00 |
| Last changed | 2010-02-19 : 11:42:30 |
| Old Darwin URL | http://www.diss.fu-berlin.de/2001/102/ |
| Static URL | http://www.diss.fu-berlin.de/diss/receive/FUDISS_thesis_000000000406 |
| NBN | urn:nbn:de:kobv:188-2001001026 |
| Statistics | |
