RESUMEN
Up-scalable coating processes need to be developed to manufacture efficient and stable perovskite-based solar modules. In this work, we combine two Lewis base additives (N,N'-dimethylpropyleneurea and thiourea) to fabricate high-quality Cs0.15FA0.85PbI3 perovskite films by blade-coating on large areas. Selected-area electron diffraction patterns reveal a minimization of stacking faults in the α-FAPbI3 phase for this specific cesium-formamidinium composition in both spin-coated and blade-coated perovskite films, demonstrating its scaling potential. The underlying mechanism of the crystallization process and the specific role of thiourea are characterized by Fourier transform infrared spectroscopy and in situ optical absorption, showing clear interaction between thiourea and perovskite precursors and halved film-formation activation energy (from 114 to 49 kJ/mol), which contribute to the obtained specific morphology with the formation of large domain sizes on a short time scale. The blade-coated perovskite solar cells demonstrate a maximum efficiency of approximately 16.9% on an aperture area of 1 cm2.
RESUMEN
The technique of alloying FA+ with Cs+ is often used to promote structural stabilization of the desirable α-FAPbI3 phase in halide perovskite devices. However, the precise mechanisms by which these alloying approaches improve the optoelectronic quality and enhance the stability have remained elusive. In this study, we advance that understanding by investigating the effect of cationic alloying in CsxFA1-xPbI3 perovskite thin-films and solar-cell devices. Selected-area electron diffraction patterns combined with microwave conductivity measurements reveal that fine Cs+ tuning (Cs0.15FA0.85PbI3) leads to a minimization of stacking faults and an increase in the photoconductivity of the perovskite films. Ultra-sensitive external quantum efficiency, kelvin-probe force microscopy and photoluminescence quantum yield measurements demonstrate similar Urbach energy values, comparable surface potential fluctuations and marginal impact on radiative emission yields, respectively, irrespective of Cs content. Despite this, these nanoscopic defects appear to have a detrimental impact on inter-grains'/domains' carrier transport, as evidenced by conductive-atomic force microscopy and corroborated by drastically reduced solar cell performance. Importantly, encapsulated Cs0.15FA0.85PbI3 devices show robust operational stability retaining 85% of the initial steady-state power conversion efficiency for 1400 hours under continuous 1 sun illumination at 35 °C, in open-circuit conditions. Our findings provide nuance to the famous defect tolerance of halide perovskites while providing solid evidence about the detrimental impact of these subtle structural imperfections on the long-term operational stability.
RESUMEN
We present unique spatial-mode switching in a cw Yb:CALGO laser when pumped at a multihundred-watts power level. It permits us to automatically stabilize to a TEM(00) mode from a highly spatial multimode regime. This stabilization is achievable thanks to polarization-mode switching allowed by the particular spectroscopic and thermal properties of Yb:CALGO crystal. This atypical and unexpected behavior is studied in detail in this Letter and explained by analysis of the thermo-optical coefficients for CALGO.
RESUMEN
We report on the first diode-pumped Yb:CaGdAlO4 regenerative amplifier in the sub-100-fs regime. It generates pulses at a central wavelength of 1047 nm with up to 24 µJ energy (after compression) at a repetition rate of 50 kHz. The measured pulse duration is 97 fs, with a spectral bandwidth of 19 nm. We describe in detail how nonlinear effects are optimally used to compensate gain narrowing in order to overcome the 100 fs barrier.