Layers of CH3NH3PbI3 are investigated by modulated surface photovoltage spectroscopy (SPV) during heating in vacuum. As prepared CH3NH3PbI3 layers behave as a p-type doped semiconductor in depletion with a band gap of 1.5 eV. After heating to 140 °C the sign of the SPV signals of CH3NH3PbI3 changed concomitant with the appearance of a second band gap at 2.36 eV ascribed to PbI2, and SPV signals related to charge separation from defect states were reduced after moderate heating.

As a promising material, CsPbX (X = Cl, Br, I) nanocrystals (NCs) have attracted much attention. However, their luminescent property is still under debate. In this work, we first systematically studied the colloidal preparation of CsPbX NCs. It is found that the critical parameter for the formation of CsPbX NCs is the ratio between Cs and Pb. Pure CsPbX NCs are nonluminescent. The luminescence property of previous reported CsPbX NCs may come from the impurity of luminescent CsPbX NCs. No coexistence of both CsPbX and CsPbX phase has been found in one single nanoparticle. The water-triggered transformation from nonluminescent CsPbX NCs to luminescent CsPbX NCs has been quantitatively studied. The potential application of CsPbX NCs in humidity sensor and anticounterfeiting have been demonstrated. This work is important because it not only confirmed the nonluminescent nature of CsPbX NCs but also demonstrated the potential application of such NCs.

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To analyze the dominant recombination, researchers often consider the diode ideality factor (nid), determined from the fitting of a semi‐log plot of light intensity–dependent open‐circuit voltage (Voc(lnI/I0)) to a linear dependence. This value is called “nid,Voc”. Theoretically, nid is the exponential dependence factor in the recombination rate function of the split of quasi‐Fermi levels. This nid is called “nid,C”. Herein, correlations between nid,Voc, nid,C, and the dominant recombination are reconsidered using a validated numerical drift–diffusion model and a diode current analysis in perovskite solar cell devices having accumulations of charged defects near the carrier transporting interfaces. It is found that the interplay between the recombination processes affects the linearity of the Voc(lnI/I0) plots. Devices having a single dominant recombination process exhibit Voc(lnI/I0) plots that appear to be linear, resulting in nid,Voc ≈ nid,C of the dominant recombination. Conversely, bends in the Voc(lnI/I0) curves indicate that different (multiple) recombination mechanisms dominate at different light intensities, so nid,Voc is an effective nid of the total diode current whose value is not consistent with any nid,C values. This work provides more understanding of nid and how to interpret a Voc(lnI/I0) curve more correctly for the insights into recombination mechanisms.

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A simple deposition process for preparing crystalline semiconductors with low degrees of disorder is of paramount interest for both device applications and research investigations. This study centers on the ultrasonically sprayedaerosol based approach for preparing crystals of methylammonium lead trihalide perovskite (CH 3 NH 3 PbI 3 ). The surface photovoltage (SPV) spectra are found to depend strongly on the preparation conditions, with the SPV signals (below the material's band gap) providing information on the defect states. The measured values of tail states near the band gap (E t ) are found to be about 21 and 52 meV for the CH 3 NH 3 PbI 3 crystals prepared by the ultrasonically sprayed-on and spun casting approaches, respectively.

Low dimensional perovskites via DMF : DMSO = 8 : 2 with potential for semi-transparent solar cell led to superior surface morphology with large crystallite size and low defects.

In solution-processed perovskite semiconductors, ultraviolet (UV) radiation can induce structural degradation in the light-absorbing layer, for instance, methylammonium lead iodide (MAPbI 3 ). In this paper, we use modulated surface photovoltage (SPV) spectroscopy to track the mechanisms of photo-generated charge generation and separation as well as the formation of defects in formamidinium lead triiodide (FAPbI 3 ) and cesium (Cs)-containing FAPbI 3 (FA x Cs 1−x PbI 3 ) perovskite when exposed to different durations of UV-light treatment. The measured SPV signals (inphase and out-phase (shifted by 90°)) were found to be strongly dependent on the addition of Cs and on the UV exposure times. Upon the partial incorporation of Cs, the improved stability in the structural and optical properties was observed. The formation of the δ-CsPbI 3 phase in the FA x Cs 1−x PbI 3 perovskite is attributed to the stabilization of the FAPbI 3 /CsPbI 3 interface, which would efficiently inhibit the phase segregation and provide for a stable medium for the modulated charge separation under UV illumination.