Topas twins

TA spectra of the perovskite thin films were measured by a femtosecond pump-probe system with a homebuilt TA spectrometer described in our previous publication (8 (link)). Laser pulses at 1030 nm with ~200-fs duration were generated by a 400-kHz amplified Yb:KGW laser system (PHAROS, Light Conversion Ltd.). The probe beam was a white-light continuum beam spanning 450- to 950-nm spectral region, created by focusing 5% of the 1030-nm fundamental output onto a YAG (yttrium aluminum garnet) crystal (4.0 mm thick). The rest of the output pumps an optical parametric amplifier (OPA; TOPAS-Twins, Light Conversion Ltd.) to generate pump pulses at 400 nm (3.1 eV).

Two independent OPAs (TOPAS-Twins, Light Conversion Ltd.) pumped by the output of a high-repetition rate amplifier (400 KHz, PHAROS, Light Conversion Ltd.) provided the pump and probe beams. One OPA provided the pump, and the other supplied the probe. An acousto-optic modulator (R23080-1, Gooch and Housego) was used to modulate the pump beam at 100 kHz. A mechanical translation stage (DDS600-E, Thorlabs) was used to delay the probe with respect to the pump. Both the pump and probe beams were spatially filtered before being focused onto the sample by a 40× (NA, 0.60) objective (CFI Apo TIRF, Nikon Inc.) The probe beam was collected by the same objective and was detected by an avalanche photodiode (APD) (C5331-04, Hamamatsu). The change in the probe reflectance (ΔR) induced by the pump was detected by a lock-in amplifier.

Steady-state and time-resolved PL measurements have been performed by a home-built confocal micro-PL setup. A picosecond-pulsed diode laser (LDH-P-C-450B, PicoQuant) with and excitation energy of 2.8 eV (full width at half maximum, 50 ps) was used to excite the sample, which was focused by a 50× [numerical aperture (NA), 0.95] objective. The beam size in PL measurements was ~1 μm, smaller than our sample size. The PL emission was collected with the same objective, dispersed with a monochromator (Andor Technology), and detected by a thermoelectric-cooled charge-coupled device (Andor Technology). Time-resolved PL was measured using a single-photon avalanche diode (PDM series, PicoQuant) and a single-photon counting module (PicoQuant). The time resolution of the time-resolved PL setup is ~100 ps. Measurements with excitation energy of 2.1 eV were carried out with an optical parametric amplifier (OPA; TOPAS-Twins, Light Conversion Ltd) pumped by a high-repetition rate amplifier (400 KHz, PHAROS, Light Conversion Ltd.).