| Renewable energy including the photovoltaic power has supported by the Government policies. The solar cell is the core of the photovoltaic system. CdTe is a near perfect material for PV application since it is a direct band gap semiconductor with a high optical absorption coefficient in the visible portion of the photon spectrum. The highest efficiency16.5%of CdTe/CdS thin film solar cell has a large distance from its theoretical limit-28%which indicates that there is a much space to improve the performance of this device. On the basis of commercial ITO glass, we deposited the CdS films using CBD method, and then grown the CdTe polycrystalline by CSS method. Finally, we deposited the back contact layer CuxTe using vacuum evaporation method. We produce a CdTe thin film solar cell and analyze the crucial factor which could affect the performance of this device.After introducing the basic properties of related materials of CdTe solar cell and several technologies, we analyze the function of each layer of thin film solar cell focusing on the light-induced carriers’ collection.With the help of adding oxidant into the reaction solution, we improve the optical and morphological properties of the CdS window layer by chemical bath deposition (CBD). Then, we systematically investigate the structural, morphological, optical and electrical properties of CdS films. Our result shows that the oxidant destroys the complex making the CdS grain size as small as20nm. The quantum confinement effects appear at this size and increase the band gap of CdS. The large bandgap allows more photons to pass through the window layer and contribute to the photocurrent which could improve the open-circle voltage and short-circle current.Second, we investigated the CdTe films grown by close space sublimation (CSS) in order to understand the effect of oxidation and CdCl2activation on the structural, morphological and electrical properties of CdTe. The results show that the introduction of O2during the deposition promotes the nucleation of CdTe and decreases the preferential orientation in the (111) plane, and the O2could also reduce the grain size because the nucleation process is enhanced. Furthermore, the oxidation lowers the level of valence band of CdTe so that a hole-barrier formed in the grain boundaries which hinder the motion of hole-carriers. The CdCl2activation makes the grain boundaries passivation and shifts the top of valence band to a higher level, so the activation is like a p-doping process. The oxygen-assistant CdTe growth, together with the CdCl2passivation may efficient to fabricate the CdTe film solar cells.Finally, we produce a CdTe thin film solar cell and discuss the key point of its technology. Intermixing at the CdS/CdTe interface is crucial for device performance, as it is expected to reduce the effect of lattice mismatch by formance a graded layer at the interface. It needs a high-temperature growth processing or a post-heat treatment with CdCI2. CuxTe is one the most commonly used conductive back contact materials. It can reduce the barrier height caused by high CdTe work function and eliminate the "Roll-over". The collection of minority carrier will also be enhanced by a proper back contact layer.In the end, we produce a CdTe thin film solar cell with the efficiency of9.3%successfully. |
PDF Full Text Request