Nickel Oxide Hole‐Selective Heterocontact for Silicon Solar Cells: Role of SiO_x Interlayer on Device Performance

Abstract

Carrier‐selective contact‐based silicon heterojunction solar cells are fabricated using nickel oxide (NiOx) as a hole‐selective layer by thermal evaporation. The highest power conversion efficiency of ≈15.20% with a chemically grown SiOx interlayer is achieved from a Ag/ITO/NiOx/n‐Si/LiFx/Al cell structure in comparison with ≈12.43% without SiOx. The cells without and with the SiOx layer are analyzed by considering crucial parameters for conversion efficiency, such as minority carriers' diffusion lengths, lifetimes, recombination resistance, and density of interface defect states at the NiOx/n‐Si junction, by studying the dark/light current density–voltage, quantum efficiency, impedance, and parallel conductance characteristics. Device analysis provides evidence for the cell's open‐circuit voltage and short‐circuit current enhancement with the SiOx interlayer. This is due to an improvement in minority carrier lifetimes from ≈8.6 to ≈48.27 μs (photo‐conductance decay analysis), which is also estimated from ≈7.45 to ≈49.20 μs by impedance spectra analysis, increased minority carrier diffusion length from ≈171 to ≈952 μm, and decreased rear surface recombination velocity from ≈1106 to ≈170 cm s−1 (quantum efficiency analysis). These investigations reveal that engineering the n‐Si/LiFx interface by the SiOx interlayer is more important than the NiOx/n‐Si interface because of a thin unintentionally grown SiOx layer during NiOx evaporation simultaneously mediating silicon surface passivation.

Evaluating Materials Design Parameters of Hole-Selective Contacts for Silicon Heterojunction Solar Cells

“…Even the case with the lowest D it is still over an order of magnitude worse than the performance modeled in the (p) a-Si:H cell. Nayak et al have recently achieved higher performing cells with a NiO x p-layer [22], which is probably due to better passivation and lower D it , but we note that this device architecture does not use an intrinsic a-Si:H layer, so our simulation is not directly transferable here. This corroborates our simulations from Fig.…”

“…However, as shown recently, it is also possible that SiO x is forming at the interface without a significant detrimental effect on passivation [62]. In fact, Nayak et al reported that an intentionally introduced SiO x layer actually improves the solar cell performance in (n) c-Si / (i) SiO x / (p) NiO x devices [22]. The implications for an (n) c-Si / (i) a-Si:H / (i) SiO x / (p) NiO x device remain to be explored.…”

“…The previous literature has assumed the valence band (VB) edge alignment to crystalline silicon (c-Si) as a principle design parameter; therefore, we select nickel oxide (NiO x , with a VB edge energy E VB,NiO x close to that of c-Si, E VB,c-Si ) as a test hole-selective contact material for both simulations and experiments in a full device stack. NiO x has only rarely been studied as a hole-selective contact in SHJ solar cells [21], [22]. There are only a few reports of solar cell performance, and highest reported efficiencies up to 12.4% and open-circuit voltage (V OC ) values up to 510 mV [22].…”

“…NiO x has only rarely been studied as a hole-selective contact in SHJ solar cells [21], [22]. There are only a few reports of solar cell performance, and highest reported efficiencies up to 12.4% and open-circuit voltage (V OC ) values up to 510 mV [22]. Most notably, its tunable VB edge energy and facile growth conditions make it a suitable test material.…”

RF magnetron sputtered NiO<sub><italic>x</italic></sub> and NiO<sub><italic>x</italic></sub>/c-Si single-side heterojunction solar cells

“…率最高的 HCT 太阳电池。相比 p + :a-Si 发射层的 HJT 电池，其短路电流密度 J SC 提高了 1.3 mA/cm 2 。p 型半导体材料 NiO x [13,14] , Cu 2 O x [15] 的研究较为少见，目前报道的最高效率是印度 理工学院德里分校 Nayak 等人 [13] 以热蒸发 NiO x 为发射极，LiF x 为背场结制备的晶硅异质 结电池，其效率达到 15.20%。南开大学 Yang 等人 [14]…”