It is still a challenge to fabricate a smooth, high-quality perovskite film under ambient conditions via an inkjet printing process. Here, we report a systematic study of the fabrication of one-step inkjet-printed metal halide perovskite (IJP-MHP) films under ambient conditions. An inkjet-printed perovskite film with full surface coverage and large columnar grains was obtained through in situ heat treatment, self-vapor annealing (self-VA), and solvent engineering. An efficiency of 13.44% was achieved for the perovskite solar cell (PSC) with an architecture of FTO/IJP-SnO x /IJP-MHP/IJP-spiro-OMeTAD/Au. Furthermore, an ink additive polyvinylpyrrolidone (PVP) and antisolvent extraction treatment were carried out to retard perovskite nucleation and grain growth. Resulting perovskite films with improved film morphology and uniformity were obtained, although they delivered no competitive performance. Further optimization can be conducted to improve efficiency by careful selection of ink additives.

Planar perovskite solar cells (PSCs) based on low-temperature solution-processed SnO<inf>2</inf> electron transport layers (ETLs) usually suffer from energy losses within SnO<inf>2</inf> ETLs or at SnO<inf>2</inf>/perovskite interfaces. Doping is an effective strategy to modify the properties of SnO<inf>2</inf> and reduce such energy losses. Herein, Ce ions are incorporated into solution-processed SnO<inf>x</inf> and Ce-doped SnO<inf>x</inf> ETLs are fabricated for planar PSCs via inkjet printing. The Ce-doped SnO<inf>x</inf> ETL shows enhanced conductivity and improved energy level alignment with the perovskite layer, which can facilitate charge extraction and transport capabilities. Ce doping also effectively passivates the surface defects of SnO<inf>x</inf>. The photoluminescence characterization reveals that the carrier recombination is suppressed within the perovskite film. As a result, an improved power conversion efficiency (PCE) of 15.77% is obtained for the planar PSC with a Ce-doped SnO<inf>x</inf> ETL, compared to that of 14.66% for the undoped device. Furthermore, this work demonstrates a sustainable fabrication method which has great potential for the upscaling of PSCs.

Inkjet printing is a more sustainable and scalable fabrication method than spin coating for producing perovskite solar cells (PSCs). Although spin-coated SnO2 has been intensively studied as an effective electron transport layer (ETL) for PSCs, inkjet-printed SnO(2 )ETLs have not been widely reported. Here, we fabricated inkjet-printed, solution-processed SnOx ETLs for planar PSCs. A champion efficiency of 17.55% was achieved for the cell using a low-temperature processed SnOx ETL. The low-temperature SnOx exhibited an amorphous structure and outperformed high-temperature crystalline SnO2. The improved performance was attributed to enhanced charge extraction and transport and suppressed charge recombination at ETL/perovskite interfaces, which originated from enhanced electrical and optical properties of SnOx, improved perovskite film quality, and well-matched energy level alignment between the SnOx ETL and the perovskite layer. Furthermore, SnOx was doped with Cu. Cu doping increased surface oxygen defects and upshifted energy levels of SnOx, leading to reduced device performance. A tunable hysteresis was observed for PSCs with Cu-doped SnOx ETLs, decreasing at first and turning into inverted hysteresis afterwards with increasing Cu doping level. This tunable hysteresis was related to the interplay between charge/ion accumulation and recombination at ETL/perovskite interfaces in the case of electron extraction barriers.

Inkjet printing emerged as an alternative deposition method to spin coating in the field of perovskite solar cells (PSCs) with the potential of scalable, low-cost, and no-waste manufacturing. In this study, the materials TiO2, SrTiO3, and SnO2 were inkjet-printed as electron transport layers (ETLs), and the PSC performance based on these ETLs was optimized by adjusting the ink preparation methods and printing processes. For the mesoporous ETLs inkjet-printed from TiO2 and SrTiO3 nanoparticle inks, the selection of solvents for dispersing nanoparticles was found to be important and a cosolvent system is beneficial for the film formation. Meanwhile, to overcome the low current density and severe hysteresis in SrTiO3-based devices, mixed mesoporous SrTiO3/TiO2 ETLs were also investigated. In addition, inkjet-printed SnO2 thin films were fabricated by using a cosolvent system and the effect of the SnO2 ink concentrations on the device performance was investigated. In comparison with PSCs based on TiO2 and SrTiO3 ETLs, the SnO2-based devices offer an optimal power conversion efficiency (PCE) of 17.37% in combination with a low hysteresis. This work expands the range of suitable ETL materials for inkjet-printed PSCs and promotes the commercial applications of inkjet printing techniques in PSC manufacturing.