There has been rapid progress in solution-processed organic solar cells (OSCs) and perovskite solar cells (PVSCs) toward low-cost and highthroughput photovoltaic technology. Carrier (electron and hole) transport layers (CTLs) play a critical role in boosting their efficiency and long-time stability. Solution-processed metal oxide nanocrystals (SMONCs) as a promising CTL candidate, featuring robust process conditions, low-cost, tunable optoelectronic properties, and intrinsic stability, offer unique advantages for realizing cost-effective, high-performance, large-area, and mechanically flexible photovoltaic devices. In this review, the recent development of SMONC-based CTLs in OSCs and PVSCs is summarized. This paper starts with the discussion of synthesis approaches of SMONCs. Then, a broad range of SMONC-based CTLs, including hole transport layers and electron transport layers, are reviewed, in which an emphasis is placed on the improvement of the efficiency and device stability. Finally, for the better understanding of the challenges and opportunities on SMONC-based CTLs, several strategies and perspectives are outlined.

This study proposes a novel strategy of controllable deamination of Co–NH3 complexes in a system containing Ni(OH)2 to synthesize ultrasmall ternary oxide nanoparticles (NPs), NiCo2O4. Through this approach, ultrasmall (5 nm on average) and well‐dispersed NiCo2O4 NPs without exotic ligands are obtained, which enables the formation of uniform and pin‐hole free films. The tightly covered NiCo2O4 films also facilitate the formation of large perovskite grains and thus reduce film defects. The results show that with the NiCo2O4 NPs as the hole transport layer (HTL), the perovskite solar cells reach a high power conversion efficiency (PCE) of 18.23% and a promising stability (maintained ≈90% PCE after 500 h light soaking). To the best of the author's knowledge, it is the first time that spinel NiCo2O4 NPs have been applied as hole transport layer in perovskite solar cells successfully. This work not only demonstrates the potential applications of ternary oxide NiCo2O4 as HTLs in hybrid perovskite solar cells but also provides an insight into the design and synthesis of ultrasmall and ligand‐free NPs HTLs to enable cost‐effective photovoltaic devices.

Organic–inorganic halide hybrid perovskite materials are promising materials for X‐ray and photon detection due to their superior optoelectronic properties. Single‐crystal (SGC) perovskites have increasingly attracted attention due to their substantially low crystal defects, which contribute to improving the figures of merit of the devices. Cuboid CH3NH3PbI3 SGC with the naturally favorable geometry for device fabrication is rarely reported in X‐ray and photon detection application. The concept of seed dissolution‐regrowth to improve crystal quality of cuboid CH3NH3PbI3 SGC is proposed and a fundamental understanding of the nucleation and growth is provided thermodynamically. The X‐ray detector fabricated from cuboid CH3NH3PbI3 SGC demonstrates the firstly reported high sensitivity of 968.9 µC−1 Gy−1 cm−2 under −1 V bias. The results also show that the favorable crystal orientation and high quality of cuboid CH3NH3PbI3 leads to better responsivity and faster response speed than the more common dodecahedral CH3NH3PbI3 in photodetection. Consequently, the work paves a way to synthesize high‐quality perovskite SGCs and benefits the application of MAPbI3 SGCs with preferred crystal orientation and favorable crystal geometry for emerging device applications.

While there are very limited studies of doped ternary metal oxide based hole transport materials, a multifunctional synthesis approach of In doped CuCrO 2 nanoparticles (NPs) as efficient hole transport layers (HTLs) including simplifying the synthesis requirements is proposed, enabling doping and achievement of treatment-free HTLs. Remarkably, compared with conventional methods for synthesizing CuCrO 2 NPs, the newly proposed azeotropic promoted approach dramatically reduces the reaction time by 90% and the calcination temperature by one-third, which not only promotes high throughput production but also reduces power consumption and cost in synthesis. Equally important, indium is successfully doped into CuCrO 2 , which is fundamentally difficult in low temperature processes. The In doping offers less d-d transition of Cr 3+ and p-type doping characteristics for improving HTL transmittance and conductivity, respectively. Interestingly, In doped CuCrO 2 HTL with these improvements can be achieved by a simple ambient-condition process and exhibits thermal stability up to 200 °C, which allows perovskite solar cells (PSCs) to achieve a power conversion efficiency of 20.54%. Meanwhile, the devices show good repeatability and photostability. Consequently, the work contributes to establishing a simple approach to realize pristine and doped multinary oxides based HTL for the development of practical and high performing PSCs.

passivation have been successfully developed to improve the PV performance of PSCs. [6-10] In particular, the interface modification between CTLs and the perovskite light absorber layer always plays a pivotal role to improve the performance of PSCs.