研究目的
To evaluate one-step P2 scribing performance of picosecond laser of 532 nm wavelength for mesoscopic perovskite architecture with the c-TiO2 as the HBL and fluorine doped tin oxide (FTO) as bottom contact.
研究成果
In summary, we evaluated one-step P2 scribing performance of picosecond laser of 532 nm in wavelength for the n-i-p mesoscopic perovskite thin film solar cell architecture. One of key objectives for the P2 scribing was to completely remove the entire film stack including c-TiO2 layer while keeping the FTO layer undamaged, which is important to minimize contact resistance related to interconnecting neighboring cells. In pursuing the P2 laser scribing by picosecond laser of 532 nm wavelength, the main challenge anticipated was the low selectivity between the c-TiO2 and FTO layers. However, through laser power variation study accompanied by the SEM and EDS elemental mapping analyses, picosecond laser of 532 nm wavelength could successfully remove the c-TiO2 without damaging the FTO. Due to high optical transparency of 532 nm wavelength for the FTO, self-terminating mechanism was activated avoiding any further FTO damage upon completion of proper P2 process, and thus wider processing window was available.
研究不足
The main challenge anticipated was the low selectivity between the c-TiO2 and FTO layers for most of laser wavelengths. Complete removal of c-TiO2 is necessary while the FTO unaffected to minimize the contact resistance.
1：Experimental Design and Method Selection:
A picosecond laser of 532 nm in wavelength, ~12 ps in full-width-half-maximum temporal pulse width, 100 kHz in pulse repetition frequency (PRF) and up to 7W in average laser power, was used for this study. Laser power or pulse energy was precisely adjusted by an external attenuator set composed of a half waveplate (λ/2) and a polarizing beam splitter (PBS). Laser beam was collimated using a beam expander and coupled to a galvanometric scanner combined with a f-theta lens (telecentric, focal length of 100 mm), illuminated onto the sample from both film and substrate sides.
2：Sample Selection and Data Sources:
The n-i-p mesoscopic perovskite sample was prepared in-house. FTO deposited on glass substrate (Pilkington, TEC8) was cleaned by ultra-sonication in detergent and rinsed by DI water and IPA. The c-TiO2 layer, as the HBL, was formed on the pre-cleaned FTO substrate by spin-coating
3：15 M of TiO2 precursor solution (ShareChem) at 3000 rpm for 30 s, followed by thermal treatment at 100°C for 20 min. List of Experimental Equipment and Materials:
A picosecond laser of 532 nm in wavelength, ~12 ps in full-width-half-maximum temporal pulse width, 100 kHz in pulse repetition frequency (PRF) and up to 7W in average laser power, was used for this study. Optical microscope (F70, Mitutoyo) and scanning electron microscope (SEM, JEOL 7600F and Helios FEI Nanolab 600 Dual Beam) with energy dispersive X-ray spectroscopy (EDS) mapping were used to inspect morphology and elemental distribution of the scribed features.
4：Experimental Procedures and Operational Workflow:
The tested scribing speed was in the range of
5：1 – 1 m/s. For testing the effect of number of laser shots, single shot operation was repeated on fixed spots on the sample. Data Analysis Methods:
The elemental maps of C, I, Ti and Sn are referred to as the indicators for the states of Spiro-MeOTAD, perovskite, mp-TiO2 or c-TiO2, and FTO, respectively.
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