On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment
On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment
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DOI：
10.1088/2515-7655/ab6942
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发表时间：
2020-04-01
影响因子：
6.9
通讯作者：
Ghorbani, Elaheh
中科院分区：
文献类型：
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作者：
Ghorbani, Elaheh
地球资源丰富、环境友好的Cu-2-II-IV-VI4 （II = Sr, Ba; IV = Ge, Sn; VI = S,Se）被认为是薄膜太阳能电池吸收层的材料。通过了解和改进这些新出现的吸收剂的光电特性的尝试，在不到两年的时间里，效率提高了5.2%。然而，缓冲/吸收界面的能带对准尚未得到研究；这一信息对设计高性能器件至关重要。因此，目前的研究重点是这些材料与CdS缓冲器之间的频带偏移。利用第一性原理计算，计算了缓冲/吸收界面处的带不连续度。结果在所有Cu-2-II-IV-VI4吸收剂和CdS之间产生ii型波段对准，因此δ E-c为负。然而，在缓冲器/吸收器界面处采用负δ E-c（崖状导带偏移）会产生低开路电压和高界面相关重组。因此，有必要寻找一种与这些吸收剂形成i型带对准的替代缓冲材料，其中导带最小值和价带最大值都位于吸收剂一侧。
Earth-abundant and environmentally-friendly Cu-2-II-IV-VI4 (II = Sr, Ba; IV = Ge, Sn; VI = S,Se) are considered materials for the absorber layers in thin film solar cells. Attempts to understand and improve optoelectronic properties of these newly emerged absorbers resulted in an efficiency of 5.2% in less than two years. However, the energy band alignment at the buffer/absorber interface has not been studied yet; an information which is of crucial importance for designing high performance devices. Therefore, current study focuses on the band offsets between these materials and the CdS buffer. Using first-principles calculations, band discontinuities are calculated at the buffer/absorber interface. The results yield a type-II band alignment between all Cu-2-II-IV-VI4 absorbers and CdS, hence a negative Delta E-c. Adoption of a negative Delta E-c (cliff-like conduction band offset) at the buffer/absorber interface, however, gives rise to low open circuit voltage and high interface-related recombinations. Therefore, it is necessary to search for an alternative buffer material that forms a type-I band alignment with these absorbers, where the conduction band minimum and the valence band maximum are both localized on the absorber side.