We have demonstrated two novel donor-acceptor-donor (D-A-D) hole-transport material (HTM) with spiro[fluorene-9,9'-phenanthren-10'-one] as the core structure, which can be synthesized through a low-cost process in high yield. Compared to the incorporation of the conventional HTM of commonly used 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), the synthesis process is greatly simplified for the presented D-A-D materials, including a minimum number of purification processes. This results in an increased production yield (>55 %) and suppressed production cost (<30 $ g ), in addition to high power conversion efficiency (PCE) in perovskite solar cells (PSCs). The PCE of a PSC using our D-A-D HTM reaches 16.06 %, similar to that of Spiro-OMeTAD (16.08 %), which is attributed to comparable hole mobility and charge-transfer efficiency. D-A-D HTMs also provide better moisture resistivity to prolong the lifetime of PSCs under ambient conditions relative to their Spiro-OMeTAD counterparts. The proposed new type of D-A-D HTM has shown promising performance as an alternative HTM for PSCs and can be synthesized with high production throughput.

Fullerene-passivated SnO2 electron transport layers (ETLs) offer the route for continued boost in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs). However, the detailed understanding on the photocarrier dynamics...

Recently, a new seeding growth approach for perovskite thin films is reported to significantly enhance the device performance of perovskite solar cells. This work unveils the intermediate structures and the corresponding growth kinetics during conversion to perovskite crystal thin films assisted by seeding PbS nanocrystals (NCs), using time-resolved grazing-incidence X-ray scattering. Through analyses of time-resolved crystal formation kinetics obtained from synchrotron X-rays with a fast subsecond probing time resolution, an important "catalytic" role of the seed-like PbS NCs is clearly elucidated. The perovskite precursor-capped PbS NCs are found to not only accelerate the nucleation of a highly oriented intermediate phase, but also catalyze the conversion of the intermediate phase into perovskite crystals with a reduced activation energy E a = 47 (±5) kJ mol −1 , compared to 145 (±38) kJ mol −1 for the pristine perovskite thin film. The reduced E a is attributed to a designated crystal lattice alignment of the perovskite nanocrystals with perovskite cubic crystals; the pivotal heterointerface alignment of the perovskite crystals coordinated by the Pb NCs leads to an improved film surface morphology with less pinholes and enhanced crystal texture and thermal stability. These together contribute to the significantly improved photovoltaic performance of the corresponding devices.

Perovskite α-CsPbI3 nanocrystals (NCs) with a high fluorescence quantum yield (QY) typically undergo a rapid phase transformation to a low-QY δ-CsPbI3 phase, thus limiting their optoelectronic applications. In this study, organic molecule hexa­methyl­di­sila­thiane (HMS) is used as a unique surfactant to greatly enhance the stability of the cubic phase of CsPbI3 NCs (HMS-CsPbI3) under ambient conditions. The reaction kinetics of the phase transformation of CsPbI3 NCs are systemically investigated through in situ photoluminescence (PL), X-ray diffraction, and transmission electron microscope (TEM) measurements under moisture. The activation energy of HMS-CsPbI3 NCs is found to be 14 times larger than that of CsPbI3 NCs capped by olyelamine (OLA-CsPbI3 NCs). According to density functional theory calculations, the bonding between HMS and CsPbI3 NCs is stronger than that between OLA and CsPbI3 NCs, preventing the subsequent phase transformation. Our study presents a clear pathway for achieving highly stable CsPbI3 NCs for future applications.

This work demonstrates the direct visualization of atomically resolved quantum-confined electronic structures at organic−inorganic heterointerfaces of twodimensional (2D) organic−inorganic hybrid Ruddlesden−Popper perovskites (RPPs); this is accomplished with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) by using solvent engineering to prepare perpendicularly oriented 2D RPPs. Atomically resolved band mapping images across the organic−inorganic interfaces of 2D RPPs yield typical quantum-well-like type-I heterojunction band alignment with band gaps depending on the thicknesses or n values of the inorganic perovskite slabs. The presence of edge states within the band gap due to organic cation vacancies is also observed. In addition, real-space visualization of atomic-scale structural phase transition behavior and changes in local electronic band structures are obtained simultaneously. Our results provide an unequivocal observation and explanation of the quantumconfined electronic structures formed at organic−inorganic interfaces of 2D RPPs.