Organolead halide perovskites have attracted much interest from the scientific community in the past four years towards potential photovoltaic applications. A record efficiency of 20.1 % was reported in 2014. Some variation in efficiency is observed when the hole‐transporting material (HTM) used in perovskite solar cells (PSCs) is altered. This Review emphasizes the importance of HTMs as a means to elevate the already superior device performance to a new status. A basic introduction to perovskites as materials for photovoltaics is first provided. A plethora of HTMs used for the fabrication of these cells are then presented and the nuances of their chemistry are analyzed in detail. Finally, on the basis of the Review of HTMs, strategies that can be employed for synthesizing the “perfect” HTM for PSCs are discussed.

We report synthetic steps towards a lead free manganese based perovskite MAPbxMn1–xI1+2xCl2–2x. Fabrication of a cell with an inverted planar architecture at low processing temperatures shows its potential application in future perovskite solar cells.

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We demonstrate for the first time an entirely molecular beam epitaxy (MBE) approach to high-quality GaAs planar coalescence over embedded dielectric microstructures. Specifically, an all-MBE approach was achieved by developing a new two-stage growth process, merging the MBE growth regimes of III-flux modulated lateral epitaxial overgrowth (LEO) with self-ordered planarization of nonplanar substrates to produce highly selective planar coalescence specifically for embedding [010]-aligned silica gratings patterned on (001) substrates. The resulting planar coalescence returned a smooth (001) surface with surface roughness as low as 3 nm root-mean-square and photoluminescence (PL) equivalent to grating-free controls. In demonstrating high-quality GaAs coalescence, we also report for the first time an intentionally enhanced single InGaAs/GaAs/AlAs quantum well PL test structure seamlessly grown directly above embedded silica gratings, leading to a 1.4× enhancement in PL as a result of both Purcell and extraction enhancements corroborated by time-resolved PL studies. As a result, we provide a significant advance to the long-standing challenge of marrying high-quality semiconductor crystal growth with dielectric microstructures, unlocking several high-impact applications, such as enhanced quantum emitters and embedded metasurfaces for quantum information processing, and provide a pathway for all-MBE metamorphic III−V heteroepitaxy.