Twisted intramolecular charge transfer (TICT) chromophores exhibit a promising third-order nonlinear optical (NLO) response, γ, which is potentially useful for all-optical switching. Here we explore the third-and fifth-order NLO response of a newly synthesized chromophore, TMC-3′, which incorporates both stilbene and TICT motifs with optical function. Solution Z-scan measurements in CH 2 Cl 2 reveal modest two-photon absorptions (2PA) at 1100 and 800 nm (σ 2PA > 80 GM), and two contributions to the nonlinear refraction. The first component is attributed to the third-order bound-electronic response, while the second is assigned to a fifth-order process involving 2PA induced excited state refraction (2PA-ESR). Quantum computation suggests that the differences between the present work and previous studies lie primarily in the addition of the stilbene related states, as well as the increase in ground state dipole moment. This work yields insight into the thirdand fifth-order NLO response of TICT chromophores and demonstrates that subtle structural modifications significantly impact their functionality.
It is long recognized that high‐quality surface cleaning is critical for an increased performance of solar cells and semiconductor devices. In this contribution, the effectiveness of UV‐ozone cleaning by comparing it against the industry standard RCAand UV‐assisted deionized water (DI‐O3) techniques has been demonstrated. UV‐ozone cleaning results in an effective surface passivation quality that is comparable to both RCAand DI‐O3 cleans, realizing a recombination current density (J0) of 7 fA cm−2 as compared to 5 and 8 fA cm−2 for RCAand DI‐O3 cleans, respectively. Repeating the UV‐ozone clean on samples (i.e., growing of UV‐ozone oxide and stripping it in HF) more than twice results in a cleaning efficiency that is nearly identical to RCAclean. Based on a high resolution transmission electron microscopy analysis, the post‐annealed thickness of the UV‐ozone oxide layer was found to reduce in comparison to the pre‐annealed condition. This is likely due to oxygen diffusion from the UV‐ozone oxide layer into the overlaying AlOx layer. Additionally, it has been found that a reduction in UV‐ozone oxide deposition time to just 5 min still provides a comparable cleaning efficiency to the RCAclean, and also results in good passivation quality (5–8 fA cm−2) on both planar and textured samples.
The pinhole‐free silicon oxide (SiO
x
) layer grown using dissolved ozone in deionized water (DI‐O3) is demonstrated. An ultrathin SiO
x
layer of thickness 1.53 nm ± 1.5% is grown on silicon wafer using 7 ppm DI‐O3. A four‐step methodology, including 25 wt% aq. tetramethylammonium hydroxide (TMAH) solution at 80 °C, is employed to magnify the pinhole signatures in the underlying silicon and visualized with dark‐field optical microscopy (DFOM) and scanning electron microscopy (SEM). The DFOM images show spots on the surface of wafer that originate from airborne particles, contamination, etc. SEM images reveal the absence of etch pits in silicon even after etching of SiO
x
/silicon in TMAH for 300 s. The minority carrier lifetime and interface states density in AlO
x
‐capped SiO
x
/Si structure are ≥2 ms at carrier density of 1 × 1015 cm−3 and less than 2 × 1011 cm−2 eV−1, respectively.
Surface passivation is a key process to achieve high-efficiency in silicon solar cells. In this paper we applied UV-ozone treatment to achieve high-quality passivation on both planar and textured, n-type and p-type wafers.
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