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Methylammonium chloride (MACl) additive is almost irreplaceable in high‐performance formamidine perovskite photovoltaics. Nevertheless, Some of the problems that can arise from adding MACl are rarely mentioned. Herein, it is proposed for the first time that the addition of MACl would cause the non‐stoichiometric ratio in the perovskite film, resulting in the halogen vacancy. It is demonstrated that the non‐synchronous volatilization of methylamine cations and chloride ions leads to the formation of halogen vacancy defects. To solve this problem, the NH4HCOO is introduced into the perovskite precursor solution to passivate the halogen vacancy. The HCOO− ions have a strong force with lead ions and can fill the halogen vacancy defects. Consequently, the champion devices' power conversion efficiency (PCE) can be improved from 21.23% to 23.72% with negligible hysteresis. And the unencapsulated device can still retain >90% of the initial PCE even operating in N2 atmosphere for over 1200 h. This work illustrates another halogen defect source in the MACl‐assisted formamidine perovskite photovoltaics and provides a new route to obtain high‐performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

Abstract Zinc oxide (ZnO) as an electron transport material has been used in regular planar perovskite solar cells (PSCs). Herein, ZnO nanoparticles serve as an additive directly in perovskite active layer in order to fabricate a bulk-heterojunction inverted planar PSC. The CH 3 NH 3 PbI 3-x Cl x :ZnO bulk heterojunction is prepared by mixing ZnO nanoparticles into CH 3 NH 3 PbI 3-x Cl x precursor solution. ZnO nanoparticles act as catalytic centers and induce the growth of perovskite grains leading to the formation of large-size perovskite crystals. Remarkably, hysterysis-free power conversion efficiency of 17.26% is achieved when precisely control the concentration of ZnO nanoparticles in CH 3 NH 3 PbI x Cl 3-x :ZnO bulk heterojunction active layer. The presence of ZnO nanoparticles in the perovskite films enhances the conductivity and electron mobility. Efficient charge injection of CH 3 NH 3 PbI x Cl 3-x :ZnO film can improve charge extraction in the PSCs. Moreover, the PSCs with CH 3 NH 3 PbI x Cl 3-x :ZnO bulk heterojunction exhibit high fill factor of 77.3% and short current density of 22.71 mA cm−2, which is attributed to improved perovskite quality. The bulk heterojunction structure is fabricated by combining perovskite and metal oxides, which is of great importance to the development and commercialization of PSCs in the future. Graphical abstract Image 1 Highlights • A CH 3 NH 3 PbI 3-x Cl x :ZnO bulk heterojunction exits in the perovskite solar cell. • ZnO nanoparticles improve light harvesting efficiency of perovskite solar cell. • ZnO nanoparticles lead to the formation of large-size perovskite crystals. • ZnO nanoparticles improve conductivity and electron mobility of perovskite film. [ABSTRACT FROM AUTHOR]

SnO 2 electron transport layers (ETLs) had an essential role in the n-i-p structure of perovskite solar cells. Improving the quality of the electron transport layer and enhancing interfacial contacts were key factors in the fabrication of high-performance perovskite solar cells. Therefore, a non-ionic polymeric polyacrylamide (PAM) modified SnO 2 colloidal solution with improved clustering of SnO 2 nanoparticles was presented to form a uniform and dense SnO 2 electron transport layer. The results demonstrated that no pinhole pores were found at the interface where the PAM-modified electron transport layer and the light absorbing layer came into contact, a structure that facilitated carrier transport and reduced carrier recombination at the interface location. Further beneficial effects were revealed by femtosecond Fs-TA measurements and trap of states (tDOS) analysis, where the carrier lifetime τ 2 decreased from 306.7 ps to 137.8 ps and the trap density of states of the film also decreased significantly. Correspondingly, the SnO 2 -PAM device exhibited an optimum efficiency of 21.61 %. Fantastic device stability was obtained due to the interaction of excellent contact at the SnO 2 /FAPbI 3 interface, and 85 % of the initial efficiency was maintained when placed in air for 1000 h for photo-aging tests, thereby improving the stability of FAPbI 3 grains. This method of improving the quality of tin oxide colloidal solutions provided a novel and simple way to prepare efficient perovskite solar cells. [ABSTRACT FROM AUTHOR]

CsPbIBr 2 perovskite, as a promising light harvester, possesses the most balanced bandgap and stability characters among all-inorganic perovskite materials. However, the poor quality of the traditionally one-step solution-processed CsPbIBr 2 film always leads to a severe recombination loss and thus a low output potential difference (V oc). Herein, we demonstrate a novel vapor-assisted deposition strategy to construct high-quality CsPbIBr 2 films for the first time, in which the crystallization kinetics of the CsPbIBr 2 is more easily controllable than that of the one-step spin-coated one. The PbBr 2 film acting as the template in the CsPbIBr 2 crystal growth is firstly prepared via an antisolvent-washing technique and CsI is then vacuum evaporated onto the PbBr 2 layer. By precisely tuning the thickness of the CsI film, highly phase-pure and crystallized CsPbIBr 2 crystals are successfully obtained. The optimized CsPbIBr 2 film also exhibits a homogeneous morphology and full coverage over the substrate with large grain sizes up to microscale and ultrahigh light absorption capability. The corresponding carbon-based CsPbIBr 2 solar cells achieve a champion power conversion efficiency of 8.76% with a superior V oc of 1.289 V. The large-area (1 cm2) devices also deliver an efficiency of 6.78% with an impressive V oc of 1.336 V. Moreover, under the protection of the highly hydrophobic and chemically stable CuPc layer and carbon counter electrode, the unencapsulated devices present excellent moisture and thermal stabilities. Our work provides a new approach for the preparation of cost-effective, highly efficient and robust CsPbIBr 2 photovoltaics. Vapor-assisted deposition of CsPbIBr 2 films for highly efficient and stable carbon-based planar perovskite solar cells with superior V oc are demonstrated. A champion PCE of 8.76% with an superior V oc of 1.289 V as well as excellent moisture and thermal stabilities are achieved. Image 1 • A novel and facile vapor-assisted deposition method is developed to fabricate CsPbIBr 2 perovskites for the first time. • Highly phase-purity and crystallized CsPbIBr 2 films with large grain sizes are obtained. • A high PCE of 8.76% with a superior V oc of 1.289 V is achieved. • A PCE of 6.78% with an impressive V oc of 1.336 V is gained for the large-area (1 cm2) devices. • Excellent moisture and thermal stabilities are obtained for our devices. [ABSTRACT FROM AUTHOR]

Enhancing the optical, morphological and electronic properties of the solution-processed CsPbIBr 2 films by lithium doping for efficient carbon-based perovskite solar cells is demonstrated. The champion PCE of the CsPbIBr 2 cells is boosted from 7.41% to 9.25%, showing an increase by 24.8%. • A novel Li doping method is developed to enhance the morphological and electronic properties of the CsPbIBr 2 films. • The champion PCE of the carbon-based CsPbIBr 2 PSCs is boosted from 7.41% to 9.25% by 4% Li-doping. • Excellent moisture and thermal stabilities are obtained for the as-fabricated device. CsPbIBr 2 perovskite exhibits the most balanced bandgap and durability features among all the inorganic perovskites, showing great potential in the photoelectric field. Nevertheless, the poor film quality of the traditionally spin-coated CsPbIBr 2 restricts the further improvement of the device performance. Here, we develop a novel lithium (Li) doping strategy to promote the optical, morphological and electronic properties of the solution-processed CsPbIBr 2 perovskites. Upon incorporating Li+ ions into CsPbIBr 2 lattice, highly crystallized and well-oriented CsPbIBr 2 crystals are obtained. The as-prepared Li-doped CsPbIBr 2 exhibits a higher film coverage over the substrate with larger grains and less grain boundaries compared to the none-doped counterparts. The trap-state densities in the CsPbIBr 2 film are also effectively alleviated while the carrier lifetimes are elongated by Li doping, contributing to a lower energy loss and a higher charge collection efficiency. The optimized Li-doped perovskite solar cells (PSCs) demonstrate an excellent champion power conversion efficiency (PCE) of 9.25%, much higher than that of the none-doped devices (7.41%). Furthermore, the unencapsulated devices present a superior air and thermal stability under the protection of the hydrophobic CuPc layer and carbon electrode. Our work provides a new opportunity to fabricate cost-effective and highly efficient CsPbIBr 2 PSCs in a facile way. [ABSTRACT FROM AUTHOR]

α-Formamidinium lead iodide (α-FAPbI 3) has become one of the most promising candidate materials for stable perovskite solar cells (PSCs) owing to their outstanding optoelectronic properties and high thermal stability. The crystallinity of the active layer of perovskite is essential to the performance of perovskite solar cells. In this paper, we added lead acetate Pb(Ac) 2 as a grain growth agent into the perovskite precursor solution to prepare high-efficiency and stable perovskite solar cells. It was revealed that the crystals of Pb(Ac) 2 -modified film grew selectively along the [200] direction and that the FAPbI 3 active layer grains were arranged neatly and densely, due to the significant influence of a moderate amount of weakly acidic Ac- on the crystal growth of FAPbI 3. The relative reduction in its grain boundaries led to the decrease in the grain boundary impedance, and it was easier for electrons to perform long-range migration in the perovskite active layer. The beneficial effects of Pb(Ac) 2 were further expiored by femtosecond Fs-TA measurements and density of states (tDOS) analysis, where the carrier lifetimes τ 2 was increased from 482.4 ps to 1340 ps, and the trap density of film states was significantly reduced. The filling factor (FF) and power conversion efficiency (PCE) were increased from 76.5% and 19.7–81.1% and 21.8%, respectively, the Pb(Ac) 2 devices were placed in air for 800 h for the light aging test, and the test results still maintained 90% of the original efficiency, which improved the stability of FAPbI 3 crystals. • Pb(Ac) 2 as an additive to modulate the crystalline quality of perovskite active layer films. • Perovskite solar cell defect reduction and carrier lifetime increase by Pb(Ac) 2 modification. • The Pb(Ac) 2 -modified active layer grains have preferential orientation and orderly arrangement. • 81.1% filling factor and 21.8% efficiency are achieved for a single PSC cell with excellent stability. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid perovskite materials with distinctive optoelectronic properties have attracted much interest in the field of solar cells. As the light absorber, the quality of perovskite films is crucial to the performances of perovskite solar cells. Anti-solvent engineering seems to be an efficient method in preparing high-quality perovskite films, but mostly used anti-solvents are toxic, such as chlorobenzene (CB)， which is harmful to the environmental protection. In the present work, we used the green anti-solvent diethyl carbonate (DEC) instead of CB, demonstrated that the DEC engineered CH 3 NH 3 PbI 3 film exhibits improved morphology and crystallinity as well as reducing defects, which can be attributed to the interaction between DEC and the solvent dimethyl sulfoxide (DMSO). The DEC anti-solvent assisting yields efficient CH 3 NH 3 PbI 3 perovskite solar cells with a champion power conversion efficiency of 20.20% and a steady state efficiency of 86% over a period of 20 days of storage under ambient conditions. The present study provides a viable path way to design green and effective perovskite solar cells in the future. [Display omitted] • Developed a green solvent-assisted perovskite crystallization method. • Formed uniform and compact perovskite films with large grains. • High-quality perovskite films prepared by green anti-solvent diethyl carbonate. [ABSTRACT FROM AUTHOR]