Hole transport material free carbon-based all-inorganic CsPbBr₃ perovskite solar cells (PSCs) are promising for commercialization due to its low-cost, high open-circuit voltage (V_oc) and superior stability. Due to the different solubility of PbBr₂ and CsBr in conventional solvents, CsPbBr₃ films are mainly obtained by multi-step spin-coating through the phase evolution from PbBr₂ to CsPb₂Br₅ and then to CsPbBr₃. The scalable fabrication of high-quality CsPbBr₃ films has been rarely studied. Herein, an inkjet-printing method is developed to prepare high-quality CsPbBr₃ films. The formation of long-range crystalline CsPb₂Br₅ phase can effectively improve phase purity and promote regular crystal stacking of CsPbBr₃. Consequently, the inkjet-printed CsPbBr₃ C-PSCs realized PCEs up to 9.09%, 8.59% and 7.81% with active areas of 0.09, 0.25, and 1 cm², respectively, demonstrating the upscaling potential of our fabrication method and devices. This high performance is mainly ascribed to the high purity, strong crystal orientation, reduced surface roughness and lower trap states density of the as-printed CsPbBr₃ films. This work provides insights into the relationship between the phase evolution mechanisms and crystal growth dynamics of cesium lead bromide halide films.

Despite the rapidly increased power conversion efficiency (PCE) of perovskite solar cells (PVSCs), it is still quite challenging to bring such promising photovoltaic technology to commercialization. One of the challenges is the upscaling from small-sized lab devices to large-scale modules or panels for production. Currently, most of the efficient inverted PVSCs are fabricated on top of poly[bis(4-phenyl)(2, 4, 6-trimethylphenyl)amine] (PTAA), which is a commonly used hole-transporting material, using spin-coating method to be incompatible with large-scale film deposition. Therefore, it is important to develop proper coating methods such as blade-coating or slot-die coating that can be compatible for producing large-area, high-quality perovskite thin films. It is found that due to the poor wettability of PTAA, the blade-coated perovskite films on PTAA surface are often inhomogeneous with large number of voids at the buried interface of the perovskite layer. To solve this problem, self-assembled monolayer (SAM)-based hole-extraction layer (HEL) with tunable headgroups on top of the SAM can be modified to provide better wettability and facilitate better interactions with the perovskite coated on top to passivate the interfacial defects. The more hydrophilic SAM surface can also facilitate the nucleation and growth of perovskite films fabricated by blade-coating methods, forming a compact and uniform buried interface. In addition, the SAM molecules can also be modified so their highest occupied molecular orbital (HOMO) levels can have a better energy alignment with the valence band maxima (VBM) of perovskite. Benefitted by the high-quality buried interface of perovskite on SAM-based substrate, the champion device shows a PCE of 18.47% and 14.64% for the devices with active areas of 0.105 cm² and 1.008 cm², respectively. In addition, the SAM-based device exhibits decent stability, which can maintain 90% of its initial efficiency after continuous operation for over 500 h at 40 ℃ in inert atmosphere. Moreover, the SAM-based perovskite mini-module exhibits a PCE of 14.13% with an aperture area of 18.0 cm². This work demonstrates the great potential of using SAMs as efficient HELs for upscaling PVSCs and producing high-quality buried interface for large-area perovskite films.

There have been huge achievements of all-perovskite tandem solar cells, which recently realized the highest power conversion efficiency of 24.8%. However, the complex device structure and complicated manufacture processes severely restrict the further development of all-perovskite tandem solar cells. In this work, we successfully fabricated high-efficiency hole transport material-free (HTM-free) Sn−Pb alloyed narrow bandgap perovskite solar cells (PSCs) by introducing guanidinium thiocyanate (GASCN) and hydroiodic acid (HI) into the perovskite precursor solution. GASCN and HI play a positive synergy effect during perovskite crystallization process resulting in larger grain size, fewer surface defects, and lower trap density to suppress the Sn²⁺ oxidation degradation. Furthermore, they could effectively adjust the energy level of perovskite materials, reduce the energy level difference between perovskite and ITO resulting in more efficiently transport of free hole charge carriers. As a result, with adding GASCN and HI, the achieved highest power conversion efficiency of HTM-free devices increased from 12.58% to 17.85%, which is one of the highest PCEs among all values reported to date for the HTM-free narrow-bandgap (1.2–1.4 eV) Sn−Pb binary PSCs. Moreover, the optimized device shows improved environmental stability. Our additive strategy manifests a remarkable step towards the facile, cost-efficient fabrication of HTM-free perovskite-based tandem solar cells with both high efficiency and simple fabrication process.