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.

CsPbI2Br all-inorganic perovskite has shown superior photovoltaic properties particularly excellent phase and thermal stability, while the complicated film growth process requires additional research. Herein, the nucleation and crystallization process of the CsPbI2Br perovskite film is assisted by methyl acetate anti-solvent treatment. Additionally, a tailored SnO2 nanoparticle/TiO2 nanocrystal structured double electron transport layers (ETLs) is designed to remove the interfacial energy barrier, thus enhancing charge transfer and decrease charge recombination at the CsPbI2Br/ETL interfaces. Through synergistically dual interfacial engineering, we have demonstrated the preparation of a compact CsPbI2Br polycrystalline film with ordered and homogeneous grain size as well as ideal interfacial energy level alignment. In consequence, stable CsPbI2Br all-inorganic perovskite solar cells with the best power conversion efficiency of 15.86% has been successfully achieved together with a high open-circuit voltage of 1.23 V and a fill factor of 82.29%. We believe that the results here demonstrate efficient approaches to achieve high-quality inorganic perovskites for promoting their optoelectronic applications.

Polymer–polymer blends have been reported to exhibit exceptional thermal and ambient stability. However, power conversion efficiencies (PCEs) from devices using polymeric acceptors have been recorded to be significantly lower than those based on conjugated molecular acceptors. Herein, two organic nonfullerene bulk heterojunction (BHJ) blends ITIC:PBDB‐T and N2200:PBDB‐T, together with their fullerene counterpart, PCBM:PBDB‐T, are adopted to understand the effect of electron acceptors on device performance. Free charge carrier properties using time‐resolved microwave conductivity (TRMC) measurements are comprehensively investigated. The nonfullerene devices show an improved PCE of 10.06% and 6.65% in the ITIC‐ and N2200‐based cells, respectively. In comparison, the PCBM:PBDB‐T‐based devices yield a PCE of 5.88%. The optimal N2200:PBDB‐T produced the highest TRMC mobility, longest lifetime, and greatest free‐carrier diffusion length. It is found that such phenomena can be associated with the unfavorable morphology of the all‐polymer BHJ microstructure. In contrast, the solar cells using either the PCBM or ITIC acceptors display a more balanced donor and acceptor phase separation, leading to more efficient free‐carrier separation and transport in the operating device. By sacrificing efficiency for superior stability, it is shown that the improved structure in all‐polymer blend can deliver a more stable morphology under thermal stress.

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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