Halilov S, Belayneh M L, Hossain M A, Abdallah A A, Hoex B, Rashkeev S N
Qatar Environment and Energy Research Institute (QEERI) Doha Qatar
School of Photovoltaic and Renewable Energy Engineering, University of New South Wales Sydney New South Wales Australia.
RSC Adv. 2020 Jun 11;10(38):22377-22386. doi: 10.1039/d0ra02982c. eCollection 2020 Jun 10.
NiO alloyed with aluminum, Ni Al O, is analyzed in terms of its stoichiometry, electronic and transport properties, as well as interfacial band alignment with Si to evaluate its potential use as a hole transport layer (HTL) in p-i-n type solar cells. The analysis is based on component material and slab structural simulations, as well as simulated and measured angle-resolved valence-band photoemission spectroscopy (PES) data, in order to reveal the best suitable stoichiometry. It is concluded that the ionization energy from the highest occupied states tends to increase with Al content as the simulated work function grows from 4.1 eV for pure NiO to 4.7 eV for heavily alloyed AlNiO. The electronic structure as a function of the interface design between crystalline silicon and the transport layer is used to assess the band lineup and its correlation with the discontinuity of the affinities. The affinity rule is tested by evaluating the workfunctions of the component layers and justified best for a particular Ni-enriched interface design. Technology Computer-Aided Design (TCAD) device simulations show, that the band offset between oxide and crystalline silicon remains within the range of values to sustain a staggering alignment - a condition suitable for effective charge separation, similar to a situation in a tunneling diode. The self-energy of the hole carriers is estimated by contrasting simulated and measured photoemission data, which in the case of non-annealed Al-rich samples is shown to be an order of magnitude higher due to the disorder effects. The work functions derived from the measured PES data for the epitaxially grown oxide films with nearly identical alloy stoichiometry correlate well with the simulated values. The findings suggest that the optimal HTL is formed by starting with a pure Ni layer, followed by a graded doping Al Ni O, with high at contact/oxide interface and low at the oxide/semiconductor.
与铝合金化的氧化镍（NiAlO），从其化学计量、电子和输运性质以及与硅的界面能带排列方面进行分析，以评估其作为p-i-n型太阳能电池中空穴传输层（HTL）的潜在用途。该分析基于组成材料和板结构模拟，以及模拟和测量的角分辨价带光电子能谱（PES）数据，以揭示最合适的化学计量。得出的结论是，随着模拟功函数从纯NiO的4.1 eV增长到重合金化AlNiO的4.7 eV，最高占据态的电离能倾向于随着Al含量的增加而增加。作为晶体硅和传输层之间界面设计函数的电子结构用于评估能带排列及其与亲和性不连续性的相关性。通过评估组成层的功函数来检验亲和性规则，并且对于特定的富Ni界面设计最合理。技术计算机辅助设计（TCAD）器件模拟表明，氧化物和晶体硅之间的能带偏移保持在维持交错排列的值范围内——这是一种适合有效电荷分离的条件，类似于隧道二极管中的情况。通过对比模拟和测量的光电子能谱数据来估计空穴载流子的自能，在未退火的富Al样品中，由于无序效应，其显示出高一个数量级。从具有几乎相同合金化学计量的外延生长氧化膜的测量PES数据得出的功函数与模拟值相关性良好。研究结果表明，最佳的HTL是通过从纯Ni层开始，然后是渐变掺杂的AlNiO形成的，在接触/氧化物界面处高，在氧化物/半导体处低。
