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Observation and implications of the Franz‐Keldysh effect in ultrathin GaAs solar cells
Progress in Photovoltaics ( IF 8.0 ) Pub Date : 2020-05-03 , DOI: 10.1002/pip.3270
Maarten Eerden 1 , Jasper Gastel 1 , Gerard J. Bauhuis 1 , Peter Mulder 1 , Elias Vlieg 1 , John J. Schermer 1
Affiliation  

Voltage‐dependencies were observed in the external quantum efficiency (EQE) spectra of ultrathin GaAs solar cells. The subbandgap tail was shown to increase going from forward to reverse bias, while at energies above the bandgap, voltage‐dependent oscillations in the EQE were measured. Using optical simulations, it is irrefutably shown that the voltage‐dependencies are caused by the Franz‐Keldysh effect, that is, an electric field‐dependent absorption coefficient near the bandgap. The dependency on voltage of the subbandgap tail is demonstrated to be strongest in thin‐film cells with a textured rear mirror, since the absorptivity below the bandgap is enhanced by light trapping. The voltage‐dependent subbandgap tail has important implications for the use of the reciprocity relation between photovoltaic quantum efficiency and electroluminescence. It is shown that the radiative limit for the open‐circuit voltage of thin‐film cells integrated with light management schemes can be underestimated by more than 25 mV. Consequently, these cells may be assumed to be closer to the radiative limit than they really are.

中文翻译:

超薄GaAs太阳能电池中Franz-Keldysh效应的观察和意义

在超薄GaAs太阳能电池的外部量子效率(EQE)光谱中观察到电压依赖性。子带隙尾巴显示从正向偏置到反向偏置会增加,而在带隙以上的能量下,会测量EQE中与电压有关的振荡。使用光学模拟,无法避免地表明电压依赖性是由Franz-Keldysh效应引起的,即带隙附近的电场依赖性吸收系数。在带纹理的后视镜的薄膜电池中,对子带隙尾巴电压的依赖性最强,这是因为带隙以下的吸收率会因光陷阱而增强。依赖电压的子带隙尾部对光伏量子效率与电致发光之间互易关系的使用具有重要意义。结果表明,集成有光管理方案的薄膜电池开路电压的辐射极限可能被低估了25 mV以上。因此,可以假定这些单元格比实际单元格更接近辐射极限。
更新日期:2020-05-03
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