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High coverage film could be obtained from precursor film PEDOT: PSS-based inverted perovskite solar cell, via decreasing the amount of residual DMSO or mediating the evaporation rate of DMSO with continuous gradient annealing (GA) process at 65°C–85°C (heating rate of 20°C/5 min). • A remanent solvent management strategy was employed to prepare uniform film. • The influence of residual DMSO on the properties of the MAPbI 3 film was investigated. • High device reproducibility was obtained with gradient thermal annealing. Perovskite solar cells (PSCs) have been attracting tremendous attention due to ease of processing, flexibility, and high performance. Dimethyl sulfoxide (DMSO) and N, N-dimethylformamide (DMF) are the two most widely used solvents to dissolve perovskite precursors. Here, we investigate the impact of residual amount and evaporation rate of the DMSO inside the precursor films on the microstructure of the ultimate perovskite films. We decouple the DMSO and DMF solvents and demonstrate that DMSO component exhibits great and dominant influence on the final film morphology by using quasi in-situ photoluminescence (PL) measurement and X-ray diffraction (XRD) characterization of the wet films after spin-coating. Much more smooth and uniform perovskite films are obtained by careful management of remanent solvent, including decreasing residual amount by shelving the precursor films prior to heating and retarding the evaporation of the solvent via adopting a gradient annealing (GA) process. In consequence, the as-prepared PEDOT: PSS-based inverted PSCs yield a champion efficiency of 15.59% with high reproducibility. This work shows great potential in preparing high-quality perovskite films through a simple remanent solvent management engineering. [ABSTRACT FROM AUTHOR]

Lead iodide (PbI 2) as a defect passivation in perovskite thin films can reduce halide vacancies and improve the performance of perovskite solar cells. However, excess PbI 2 can hurt the device's performance. In the case of perovskite films prepared by two-step sequential deposition, excess PbI 2 is distributed on the surface of perovskite film. The photo-decomposition of PbI 2 and the formation of surface energy barriers can hinder charge transfer in the device, leading to reduced device performance and accelerated device degradation. Inspired by the use of surfactants to control the morphology of perovskite nanocrystals, a dual-functional surfactant (oleamide) was introduced to control the distribution of excess PbI 2 on perovskite films. By adding oleamide, the aggregation distribution of PbI 2 was successfully achieved at the perovskite grain boundaries (GBs), forming a Type-I band alignment and reducing the trap density, thereby prolonging the carrier lifetime. The results show that the power conversion efficiency (PCE) of the device increased from 21.23% to 23.12% after the introduction of oleamide. Compared with the control and oleamide-modified devices, the deep-level defects were reduced by about five orders of magnitude due to the Lewis-base nature of amide groups in oleamide. In addition, due to the aggregation distribution of excess PbI 2 at GBs and the hydrophobicity of oleamide, the modified device showed better stability, maintaining 83% of its initial performance after 1000 h in air. [ABSTRACT FROM AUTHOR]

Solution-processed Cu-doped SnO 2 as an effective electron transporting layer for high-performance planar perovskite solar cells are systematically studied. The energy-level of SnO 2 electron transporting layer and the crystallization of CsFAMA films exhibit dramatically different evolution trends with respect to the addition of copper. The replacement of Sn ions by copper ions in the materials result in an improvement in conductivity of Cu-doped SnO 2 , further improve the current density of the corresponding devices. A little bit of p-type CuO does a lot for SnO 2 electron transport layer and their solar cells are firstly demonstrated. [Display omitted] • The Cu-doped SnO 2 has been successfully achieved, which results in the enhanced conductivity and improved energy band position for the Cu: SnO 2 electron transport layer. • A better quality of perovskite film with enhanced crystallinity and enlarged grain size was obtained. • The doping concentration of 5 mol% was desirable for the fabricated CsFAMA solar cells with a champion PCE of 21.35%. • The PSCs device based on Cu: SnO 2 ETL delivers excellent stability under continuous light or thermal conditions. A high-quality electron transport layer (ETL) is indispensable for effective and stable planar perovskite solar cells (PSCs). Tin oxide (SnO 2) is considered the most promising alternative to TiO 2 as ETL due to its excellent optical and electrical properties. However, some of improvements need to be carried out for intrinsic SnO 2 , such as conductivity, energy loss, and lattice mismatch in the SnO 2 /perovskite interface. Herein, the Cu-doped SnO 2 (Cu: SnO 2) as ETL has been made through mixing the copper salt precursor solution with SnO 2 colloidal solution in room-temperature solution-processed. The Cu incorporated into SnO 2 increases the conductivity of ETL and uplifts the conduction band to obtain a more suitable band alignment in SnO 2 /perovskite interface for relieving the energy barrier in the charge transporting. Moreover, it further improves the quality of perovskite films with the enhanced crystallinity, enlarged grain size, which have an impact on light absorption and reduction of defect states for the perovskite layer. The power conversion efficiency (PCE) of the prepared planar PSCs with Cu:SnO 2 ETL exceeds 21%, compared with the SnO 2 -based PSCs (19.63%), and the long-term stability was improved. [ABSTRACT FROM AUTHOR]

• A simple solvent engineering strategy was employed to control morphology of PbI 2 films effectively by water processing. • Platelet-like PbI 2 films can successfully control the residual amount of PbI 2 in perovskite film. • Platelet-like PbI 2 films can control the morphology of the perovskite film and improve the device efficiency [Display omitted] The performance of organic-inorganic perovskite solar cells depends largely on the quality of perovskite film. Currently, various methods are applied to prepare the perovskite film. Among them, the two-step method is counted as a promising candidate to obtain high-quality perovskite film. In this study, we attain a special platelet-like PbI 2 films by applying pure water to cover wet PbI 2 film and standing for a period of time. The unique morphology contributes to the entry of organic cations solution into the PbI 2 and promoting its reaction with PbI 2 , which reducing the residual amount of PbI 2 in the perovskite film. Compared to the traditional two-step method, water processing method can obtain a high-quality perovskite film with enlarged grain size, improved crystallization, and prolonged carrier lifetime. As a result, the efficiency of the prepared device based on the film has increased from 17.90% without water processing to 20.14% of water processing. Which demonstrates that this solvent engineering for PbI 2 film opens up a possibility to prepare high-quality perovskite in a two-step method and obtain highly efficient perovskite solar cells. [ABSTRACT FROM AUTHOR]

Gas-quenching fabrication of perovskite films demonstrates promising compatibility for commercialization of perovskite photovoltaics. Seeking suitable ligand for the perovskite precursor inks to improve the crystalline quality of gas-quenched methylammonium free perovskite films is critical for realizing up-scalable fabrication of stable perovskite solar cells. In this work, a series of pyrrolidone-based ligands are employed in gas-quenching fabrication of FA 0.9 Cs 0.1 PbI 3 perovskite films. Optical and morphological characterizations indicate 2-pyrrolidone is the most preferred ligand to deliver a neat buried-interface as well as a light-trapping surface at the rear of the device, which maximized the light-harvesting and the photocurrent of the device. The corresponding device achieved a power conversion efficiency of 21.6% without any interfacial passivation, as well as reduced defect density from their electrical characteristics. Moreover, a more stable performance of the device is obtained with 2-pyrrolidone compared to other pyrrolidone-based ligands, demonstrating 2-pyrrolidone as a promising ligand in designing the perovskite inks for methylammonium-free perovskite solar cells. • Various pyrrolidone-based ligands are studied in gas-quenching of FA 0.9 Cs 0.1 PbI 3 films. • Bifacial optical properties of perovskite films are optimized with NP ligand. • smoother buried interface and a rougher surface contribute to enhanced light harvesting. • NP device achieved 21.6% efficiency without any interfacial passivation [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel heterogeneous lead iodide, exhibiting two (0 0 1) interplanar distances of 6.9 Å and 9.0 Å, was constructed. • The heterogeneous structure can regulate the crystallization process of PbI 2 and perovskite films. • The V OC and PCE were raised to 1.21 V and 24.24%. At present, the highest power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%, which exhibits great potential for commercial applications. Obtaining pinhole-free, superior crystal, and high-quality perovskite films with fewer defects by adjusting the lead iodide (PbI 2) intermediate films in a two-step sequential deposition has become research arousing general interest. Herein, a heterogeneous lead iodide (HLI) structure with two (0 0 1) interplanar distances (9.0 Å and 6.9 Å), can optimize the crystallization process of perovskite to get better surface morphology and is constructed by intercalated choline chloride (a kind of vitamin B4, VB4). HLI simultaneously improves the carrier lifetime of perovskite film from 1.96 µs to 3.28 µs and reduces defect state density. Together with better morphology and lower defect state density, the open circuit voltage (V OC) and PCE based on (FAPbI 3) 0.97 (MAPbBr 3) 0.03 is significantly boosted. In addition, with double-sided modification, HLI produces an excellent PCE of 24.27% with a V OC of 1.21 V. We believe that the novel heterogeneous PbI 2 structure could be a generic method to improve the efficiency of PSCs. [ABSTRACT FROM AUTHOR]

Lead halide perovskite solar cells (PSCs) have attracted intensive attention since their power conversion efficiency (PCE) increased sharply in recent years. Thereinto, triple cation perovskite (TCP) is a popular light absorption layer for PSCs due to its excellent thermal and humidity stability. However, a large amount of MA+ (≥15%) and Br- (≥15%) in TCP makes the bandgap widen drifting from the optimum value. There is some extent of a trade-off between PCE and stability for PSCs, and narrow-bandgap TCP is one of the best choices for light absorption material to achieve an optimum balance between PCE and stability. Herein, we prepared a narrow-bandgap (1.56 eV) high-quality TCP (Cs 0.05 FA 0.86 MA 0.09 Pb(I 0.97 Br 0.03) 3) film with an average grain size up to 1208 nm and corresponding PSC with high efficiency of 20.8%. Moreover, the intermediate process of the TCP film crystallization was carefully studied disclosing the critical α-Phase intermediate and corresponding roles of DMSO solvent and MACl additive through quasi-in-situ XRD in the film formation process, and the results may give critical clues to the fabrication of high-quality narrow-bandgap TCP based PSCs. • High-quality FAPbI3-based TCP film with a narrow-bandgap (1.56 eV) was successfully prepared by applying the α-phase intermediate strategy: the grain size of the film can reach 1208 nm and the carrier lifetime exceeds 3 μs. • The crytical intermediate process introduced by the synergy of DMSO and MACl was disclosed through quasi-in-situ XRD in the film formation process. • The solar cells based on the low-doping FAPbI 3 -based TCP films show high performance and good stability even without surface passivation. [ABSTRACT FROM AUTHOR]

There has been extensive investigation into phase orientation and phase distribution for improving charge transfer in 2D perovskites-based PSCs, but very few reports have focused on the enhancement of inter-phase charge transfer by passivation. In this work, a synergetic strategy is developed by introducing hydrochloric acid and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) as additives to modulate phase distribution and passivate defects in (BA) 2 (FA) n−1 Pb n I 3n+1 (n = 9) quasi-2D perovskite films. In this process, perovskite films with suppressed phase segregation and PCBM molecules coated along the grain boundaries are obtained. PCBM is found to reduce the trap density by compensating defects, which accelerate inter-phase charge transfer and restrain nonradiative recombination, resulting in improved performance of quasi-2D PSCs. As a consequence, a high PCE of 15.01% with negligible hysteresis for quasi-2D PSCs is achieved. A synergetic strategy of phase distribution control and grain boundary passivation is developed for quasi-2D perovskite solar cells. The incorporation of PCBM into quasi-2D perovskite films with uniform phase distribution improves carrier lifetime and accelerates carrier extraction, resulting in an enhanced PCE. [Display omitted] • PCBM additive modifies the anti-solvent-assisted one-step process to fabricate the quasi-2D PSCs. • Inter-phase charge transfer is improved by the cooperation of optimised concentration of PCBM. • PCE is enhanced and hysteresis is eliminated for the devices with optimised PCBM incorporation. [ABSTRACT FROM AUTHOR]