The study of the inorganic hole-transport layer (HTL) in perovskite solar cells (PSCs) is gathering attention because of the drawback of the conventional PSC design, where the organic HTL with salt dopants majorly participates in the degradation mechanisms. On the other hand, inorganic HTL secures better stability, while it offers difficulties in the deposition and interfacial control to realize high-performing devices. In this study, we demonstrate polydimethylsiloxane (PDMS) as an ideal polymeric interlayer which prevents interfacial degradation and improves both photovoltaic performance and stability of CuSCN-based PSC by its cross-linking behavior. Surprisingly, the PDMS polymers are identified to form chemical bonds with perovskite and CuSCN, as shown by Raman spectroscopy. This novel cross-linking interlayer of PDMS enhances the hole-transporting property at the interface and passivates the interfacial defects, realizing the PSC with high power-conversion efficiency over 19%. Furthermore, the utilization of the PDMS interlayer greatly improves the stability of solar cells against both humidity and heat by mitigating the interfacial defects and interdiffusion. The PDMS-interlayered PSCs retained over 90% of the initial efficiencies, both after 1000 h under ambient conditions (unencapsulated) and after 500 h under 85 °C/85% relative humidity (encapsulated).

Recently, SnO2 has been noticed as a promising material for electron-transport layer of planar perovskite solar cells. SnO2 layer presents advantages of low-temperature processability and high power-conversion efficiency, and understanding the correlations between the SnO2 properties and device performance will provide a key to realize more efficient perovskite solar cells. Herein, uniform electron-transport layer using SnO2 nanoparticles is fabricated, and the effect of annealing on the solar-cell performance is discussed. Solar cells with low-temperature processed SnO2-nanoparticle layer (below 120 °C or even at room temperature) exhibit desirable short-circuit current, open-circuit voltage, and fill factor with the highest efficiency of 19.0%. Using atomic force microscopy and ultraviolet photoelectron spectroscopy, both great surface uniformity and favorable band alignment of low-temperature processed SnO2 layer have been observed, which are responsible for the device performance. Furthermore, deep electronic-trap states at the SnO2/perovskite interface are investigated via impedance analysis. Compared to the cells processed over 160 °C, low-temperature processed cells exhibit trap states shifting toward the bandedge and reduced trap density, verifying that controlling the interfacial trap states holds a dominance on the open-circuit voltage and is a critical requisite to enable efficient perovskite solar cells. These less-defective solar cells fabricated below 120 °C show high thermal stability, suggesting further commercial applications.

Herein, underlying factors for enabling efficient and stable performance of perovskite solar cells are studied through nanostructural controls of organic−inorganic halide perovskites. Namely, MAPbI 3 , (FA 0.83 MA 0.17 )Pb(I 0.83 Br 0.17 ) 3 , and (Cs 0.10 FA 0.75 MA 0.15 )Pb(I 0.85 Br 0.15 ) 3 perovskites (abbreviated as MA, FAMA, and CsFAMA, respectively) are examined with a grain growth control through thermal annealing. FAMA-and CsFAMA-based cells result in stable photovoltaic performance, while MA cells are sensitively dependent on the perovskite grain size dominated by annealing time. Micro-/nanoscopic features are comprehensively analyzed to unravel the origin that is directly correlated to the cell performance with the applications of electronic-trap characterizations such as photoconductive noise microscopy and capacitance analyses. It is revealed that CsFAMA has a lower trap density compared to MA and FAMA through the analyses of 1/f noises and trapping/detrapping capacitances. Also, an open-circuit voltage (V oc ) change is correlated to the variation of trap states during the shelf-life test: FAMA and CsFAMA cells with the negligible change of V oc over weeks exhibit trap states shifting toward the band edge, although the power-conversion efficiencies are clearly reduced. The origins that critically affect the solar cell performance through the characterizations of shallow/deep traps with additional mobile defects in the perovskite and interfaces are discussed.

Moving away from the high-performance achievements in organometal halide perovskite (OHP)-based optoelectronic and photovoltaic devices, intriguing features have been reported in that photocarriers and mobile ionic species within OHPs interact with light, electric fields, or a combination of both, which induces both spatial and temporal changes of optoelectronic properties in OHPs. Since it is revealed that the transport of photocarriers and the migration of ionic species are affected not only by each other but also by the inhomogeneous character, which is a consequence of the route selected to deposit OHPs, understanding the nanostructural evolution during OHP deposition, in terms of the resultant structural defects, electronic traps, and nanoscopic charge behaviors, will be valuable. Investigation of the film-growth mechanisms and strategies adopted to realize OHP films with less-defective large grains is of central importance, considering that single-crystalline OHPs have exhibited the most beneficial properties, including carrier lifetimes. Critical factors governing the behavior of photocarriers, mobile ionic species, and nanoscale optoelectronic properties resulting from either or all of them are further summarized, which may potentially limit or broaden the optoelectronic and photovoltaic applications of OHPs. Through inspection of the recent advances, a comprehensive picture and future perspective of OHPs are provided.

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