The photovoltaics (PV) industry is booming, with annual growth rates well in excess of 30% per year over the last decade. This explosive growth has been driven by rapidly increasing fossil fuel prices, an almost universal acceptance of the link between global warming and human activity, the growing ...
The photovoltaics (PV) industry is booming, with annual growth rates well in excess of 30% per year over the last decade. This explosive growth has been driven by rapidly increasing fossil fuel prices, an almost universal acceptance of the link between global warming and human activity, the growing realization of a gap between the increasing global demand for energy and the ability to supply. Today’s mainstream PV technology is based on crystalline silicon wafers. Various promising cell concepts from research and development are under investigation for commercialization.
There are several high efficiency crystal silicon solar cells such as passivated emitter solar cell, passivated emitter rear solar cell, passivated emitter rear locally diffused cell, buried contact solar cell and interdigitated back contact solar cell. But, I choose the interdigitated back contact solar cell(IBC). The IBC offers several advantages compared to conventional solar cells. These advantages include the elimination of grid shadowing, improved aesthetics, and simplification of cell interconnection leading to a lower module assembly cost. Furthermore, IBC cells can be interconnected in an easier and simpler way with a higher packing density during the module fabrication. The IBC solar cells have several advantages and many researchers have studied for improving the efficiency of IBC cells. Particularly, the back surface field(BSF) and emitter on the backside are important in improving the IBC solar cell efficiency.
This thesis presets a basic process and solar cell device simulation results of a typical interdigitated back contact solar cell on silicon wafer. The influence of several parameters on device characteristics was simulated by using the a two-dimensional numerical simulation program SILVACO that allows to optimize the cell design. The ATHENA and ATLAS of SILVACO software are useful to simulate the IBC. Unlike solar cell programs based on a combination of discrete electrical components, these programs extract the electrical characteristics of a solar cell based on virtual fabrication of its physical structure, allowing direct manipulation of materials, dimensions, and doping concentrations. Thus, this simulation program was used to design and analyze the results. By changing the values of substrate thickness, surface recombination velocity, resistivity, anti reflective coating thickness, emitter doping concentration and pitch to improve conversion efficiency.
From the simulation results, the adequate substrate thickness of the crystalline silicon back point contact solar cell for the highest efficiency was 100 ㎛. It is well known that the influence of surface recombination velocity is very high and hence its value was cited from the previous reports. The higher substrate resistivity generally offers a higher efficiency because the minority carrier lifetime is longer and hence the short circuit current can become longer. The efficiency and short circuit current density show best results when the substrate doping concentration is 1015/cm3.The oxide ARC provides higher efficiency than the nitride ARC because, the recombination velocity at the Si/SiO2 of interface is lower than the recombination velocity at the Si/Si3N4 interface. The emitter region on the backside is important region because this area makes a pn junction and the doping concentration and junction depth of this region will affect the efficiency of the back contact solar cell. Therefore, the doping concentration and pitch of the IBC solar cell were varied in order to see the effect of them on the IBC solar cell efficiency.
By varying doping concentration and the pitch of the emitter and BSF, the IBC solar cell efficiency changed. The efficiency and short circuit current density show best results when the emitter doping concentration is 5×1016/cm3. But, the carrier recombination rate also increases with emitter doping concentration. When the emitter doping concentration is over 5×1016/cm2, the recombination loss is higher than the gain of sheet resistance. The values of the efficiency and the short circuit current density are 11.1% and 22.2 mA/cm2. The efficiency and current density increase with pitch. The increasing emitter region presents increasing collection probability. The values of solar cell efficiency and short circuit current density are 11.61% and 23.8 mA/cm2. But, the variation of increasing reduces over 70 ㎛ pitch because of recombination loss. The collection probability of carriers generated in the depletion region is unity as the electron-hole pair are quickly swept apart and collected by the electric field. However, away from the pn junction, the collection probability drops. The carrier is generated more than a diffusion length away from the junction, the collection probability of this carrier is low. In other words, the probability of recombination loss is high.
In conclusion, there are several parameters to decide performance of IBC solar cell. Among these parameters, we have to consider emitter doping concentration and pitch to improve conversion efficiency and to reduce cost. The best efficiency of 11.61% was obtained for the IBC solar cell with
emitter doping concentration of 5×1016/cm3, pitch of 90 ㎛. If we control the adequate emitter doping concentration and pitch, it is easy to gain high efficiency. In addition, the pitch is related to substrate cost. From the results of simulation, the proposed doping concentration and pitch are expected to apply high efficiency and low cost IBC solar cell.
The photovoltaics (PV) industry is booming, with annual growth rates well in excess of 30% per year over the last decade. This explosive growth has been driven by rapidly increasing fossil fuel prices, an almost universal acceptance of the link between global warming and human activity, the growing realization of a gap between the increasing global demand for energy and the ability to supply. Today’s mainstream PV technology is based on crystalline silicon wafers. Various promising cell concepts from research and development are under investigation for commercialization.
There are several high efficiency crystal silicon solar cells such as passivated emitter solar cell, passivated emitter rear solar cell, passivated emitter rear locally diffused cell, buried contact solar cell and interdigitated back contact solar cell. But, I choose the interdigitated back contact solar cell(IBC). The IBC offers several advantages compared to conventional solar cells. These advantages include the elimination of grid shadowing, improved aesthetics, and simplification of cell interconnection leading to a lower module assembly cost. Furthermore, IBC cells can be interconnected in an easier and simpler way with a higher packing density during the module fabrication. The IBC solar cells have several advantages and many researchers have studied for improving the efficiency of IBC cells. Particularly, the back surface field(BSF) and emitter on the backside are important in improving the IBC solar cell efficiency.
This thesis presets a basic process and solar cell device simulation results of a typical interdigitated back contact solar cell on silicon wafer. The influence of several parameters on device characteristics was simulated by using the a two-dimensional numerical simulation program SILVACO that allows to optimize the cell design. The ATHENA and ATLAS of SILVACO software are useful to simulate the IBC. Unlike solar cell programs based on a combination of discrete electrical components, these programs extract the electrical characteristics of a solar cell based on virtual fabrication of its physical structure, allowing direct manipulation of materials, dimensions, and doping concentrations. Thus, this simulation program was used to design and analyze the results. By changing the values of substrate thickness, surface recombination velocity, resistivity, anti reflective coating thickness, emitter doping concentration and pitch to improve conversion efficiency.
From the simulation results, the adequate substrate thickness of the crystalline silicon back point contact solar cell for the highest efficiency was 100 ㎛. It is well known that the influence of surface recombination velocity is very high and hence its value was cited from the previous reports. The higher substrate resistivity generally offers a higher efficiency because the minority carrier lifetime is longer and hence the short circuit current can become longer. The efficiency and short circuit current density show best results when the substrate doping concentration is 1015/cm3.The oxide ARC provides higher efficiency than the nitride ARC because, the recombination velocity at the Si/SiO2 of interface is lower than the recombination velocity at the Si/Si3N4 interface. The emitter region on the backside is important region because this area makes a pn junction and the doping concentration and junction depth of this region will affect the efficiency of the back contact solar cell. Therefore, the doping concentration and pitch of the IBC solar cell were varied in order to see the effect of them on the IBC solar cell efficiency.
By varying doping concentration and the pitch of the emitter and BSF, the IBC solar cell efficiency changed. The efficiency and short circuit current density show best results when the emitter doping concentration is 5×1016/cm3. But, the carrier recombination rate also increases with emitter doping concentration. When the emitter doping concentration is over 5×1016/cm2, the recombination loss is higher than the gain of sheet resistance. The values of the efficiency and the short circuit current density are 11.1% and 22.2 mA/cm2. The efficiency and current density increase with pitch. The increasing emitter region presents increasing collection probability. The values of solar cell efficiency and short circuit current density are 11.61% and 23.8 mA/cm2. But, the variation of increasing reduces over 70 ㎛ pitch because of recombination loss. The collection probability of carriers generated in the depletion region is unity as the electron-hole pair are quickly swept apart and collected by the electric field. However, away from the pn junction, the collection probability drops. The carrier is generated more than a diffusion length away from the junction, the collection probability of this carrier is low. In other words, the probability of recombination loss is high.
In conclusion, there are several parameters to decide performance of IBC solar cell. Among these parameters, we have to consider emitter doping concentration and pitch to improve conversion efficiency and to reduce cost. The best efficiency of 11.61% was obtained for the IBC solar cell with
emitter doping concentration of 5×1016/cm3, pitch of 90 ㎛. If we control the adequate emitter doping concentration and pitch, it is easy to gain high efficiency. In addition, the pitch is related to substrate cost. From the results of simulation, the proposed doping concentration and pitch are expected to apply high efficiency and low cost IBC solar cell.
주제어
#solar cell
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