No abstract

An efficient electron transport layer (ETL) plays a key role in promoting carrier separation and electron extraction in planar perovskite solar cells (PSCs). An effective composite ETL is fabricated using carboxylic‐acid‐ and hydroxyl‐rich red‐carbon quantum dots (RCQs) to dope low‐temperature solution‐processed SnO2, which dramatically increases its electron mobility by ≈20 times from 9.32 × 10−4 to 1.73 × 10−2 cm2 V−1 s−1. The mobility achieved is one of the highest reported electron mobilities for modified SnO2. Fabricated planar PSCs based on this novel SnO2 ETL demonstrate an outstanding improvement in efficiency from 19.15% for PSCs without RCQs up to 22.77% and have enhanced long‐term stability against humidity, preserving over 95% of the initial efficiency after 1000 h under 40–60% humidity at 25 °C. These significant achievements are solely attributed to the excellent electron mobility of the novel ETL, which is also proven to help the passivation of traps/defects at the ETL/perovskite interface and to promote the formation of highly crystallized perovskite, with an enhanced phase purity and uniformity over a large area. These results demonstrate that inexpensive RCQs are simple but excellent additives for producing efficient ETLs in stable high‐performance PSCs as well as other perovskite‐based optoelectronics.

2D Ruddlesden−Popper (2DRP) tin (Sn) perovskite solar cells (PSCs) play an irreplaceable role in advancing the commercialization of perovskite-based photovoltaic devices due to their low toxicity and improved stability. However, the efficiency of 2DRP Sn PSCs has not made a breakthrough owing to incompletely oriented crystal growth and poor film morphology, which is limited by a complex and uncontrollable crystallization process. Here, we first introduce the mixed spacer organic cations [n-butylamine (BA) and phenylethylamine (PEA)] in 2DRP Sn perovskite to control the crystallization process. We find that when the BA + and PEA + cowork to form [(BA 0.5 PEA 0.5 ) 2 FA 3 Sn 4 I 13 ] 2DRP perovskites, the intermediate phase impeding the homogeneous and ordered nucleation of the crystal is suppressed effectively, thus enabling a high-quality film morphology and improved crystal orientation. Benefitting from it, the power conversion efficiency (PCE) is improved to 8.82%, which is the highest one among the 2DRP Sn PSCs as far as we known.

Solution-processed metal-halide perovskites have demonstrated immense potential in photovoltaic applications. Inkjet printing is a facile scalable approach to fabricate large-area perovskite solar cells (PSCs) due to its costeffectiveness and near unity material utilization ratio. However, controlling crystallinity of the perovskite during the inkjet printing remains a challenge. The PSCs deposited by inkjet printing typically have much lower power conversion efficiencies (PCEs) than those by spin-coating. Here, we show that high-quality perovskite films could be inkjet-printed with an innovative vacuum-assisted thermal annealing post-treatment and optimized solvent composition. High-performance PSCs based on printed CH 3 NH 3 PbI 3 with a PCE of 17.04% for 0.04 cm 2 (13.27% for 4.0 cm 2 ) and negligible hysteresis (lower than 1.0%) are demonstrated. These efficiencies are much higher than the previously reported ones using inkjet-printing ( 12.3% for 0.04 cm 2 ). The inkjet printing combined with vacuum-assisted thermal annealing could be an effective low-cost approach to fabricate high-performance perovskite optoelectronic thin film devices (including solar cells, lasers, photodetectors, and light-emitting diodes) with high-volume production.Metal-halide perovskites possess extraordinary photovoltaic desired features, including high charge carrier mobilities, [1][2][3] low exciton binding energies, [4][5] long charge carrier diffusion lengths, [6] broad light absorption spectra, large absorption coefficient, [7,8] and low-cost solution processability. [9] Therefore, the metal-halide perovskites have been considered as a new type promising light harvesting materials for the third generation photovoltaic applications. Notably, the power conversion efficiency (PCE) of the perovskite solar cell (PSC) has boosted from 3.8% to the certified 22.7% within the past 8 years and approached the performance of representative traditional solar cells based on crystallized silicon, cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). PSCs have demonstrated unbelievable developing speed and a bright prospect in photovoltaics. [10][11] However, most of the perovskite layers studied so far are deposited via the nonscalable spin-coating method with low material utilization ratio, [12][13][14] which hinders the commercialization of PSCs. To fabricate large-area and uniform perovskite films, a variety of film deposition technologies, including vapor assisted deposition, [15][16][17] spray-deposition, [18] soft-cover deposition, [19] brushpainting, [20] blade-coating, [21][22][23] slot-die coating, [24][25][26] and inkjet printing, [27][28][29][30][31][32][33] have been explored. Among these techniques, inkjet printing has been considered as a facile scalable approach to fabricate large-area PSCs for its cost-effectiveness, high writing accuracy, and near unity material utilization ratio. [34][35][36] Up to now, perovskite films have been inkjet printed with onestep method (e.g., print CH 3 NH 3 PbI 3 (MAPbI 3 ) pre...