Studies on the photoelectronic properties of perovskite solar cells (PSCs) made from non‐PbI2 precursors are seldom reported. In this study, a series of transient techniques are applied to investigate the charge recombination and trap distribution in an efficient PSC fabricated using a low‐toxicity Pb(NO3)2/water protocol. A device with identical conversion efficiency fabricated using a conventional PbI2/dimethylformamide protocol is also studied for comparison. Transient photovoltage and time‐resolved photoluminescence analysis reveal that the Pb(NO3)2/water‐based device exhibits a long lifetime in both bimolecular and trap‐assisted recombination. However, differential capacitance and differential charging analysis indicate that there are more charges stored in the Pb(NO3)2/water‐based perovskite layer, which stretches the energy tail from band edge to midband and should provoke serious trap‐assisted recombination. The exceptional long electron lifetime in the Pb(NO3)2/water‐based device is explained by a benign defect inactivation, which originates from water and NO3− residues from the aqueous precursor solution and is involved in the formation of perovskite crystal. Consequently, despite the perovskite film made from Pb(NO3)2/water protocol possessing high trap density, its photovoltaic device still exhibits a long electron lifetime and superior photovoltaic properties.
Mixed (FAPbI3)0.92(MAPbBr3)0.08 perovskite thin films exhibit strong nonlinear optical responses, rendering them promising candidates for applications in photonics and optical communications. In this work, we present a systematic study on the ultrafast third-order nonlinear optical processes in mixed perovskite nanocrystals (NCs) by exploring the generation of third harmonic radiation and giant two-photon absorption-based photoluminescence (PL) when excited by femtosecond laser pulses of a 1030 nm central wavelength. A comparative analysis of the coherent third harmonic generation in the thin-film-containing perovskite nanocrystals has shown a 40× enhancement of the third harmonic signal compared to the signal generated in the pure quartz substrate. The cubic dependence of the third-nonlinear optical response of the (FAPbI3)0.92(MAPbBr3)0.08 perovskites on the intensity of the driving radiation was identified using broadband 38 femtosecond driving pulses. The positive nonlinear refractive index (γ = +1.4 × 10−12 cm2·W−1) is found to play an important role in improving the phase-matching conditions of the interacting pulses by generating a strong third order harmonic. The giant two-photon absorption (TPA)-assisted PL peak was monitored and a blue shift of the PL was obtained in the higher intensity range of the laser pulses, with the absorption coefficient β estimated to be~+7.0 cm·MW−1 at a 1030 nm laser wavelength.
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