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Perovskite solar cells with the formula FA 1− x Cs x PbI 3 , where FA is formamidinium, provide an attractive option for integrating high efficiency, durable stability and compatibility with scaled-up fabrication. Despite the incorporation of Cs cations, which could potentially enable a perfect perovskite lattice 1 , 2 , the compositional inhomogeneity caused by A-site cation segregation is likely to be detrimental to the photovoltaic performance of the solar cells 3 , 4 . Here we visualized the out-of-plane compositional inhomogeneity along the vertical direction across perovskite films and identified the underlying reasons for the inhomogeneity and its potential impact for devices. We devised a strategy using 1-(phenylsulfonyl)pyrrole to homogenize the distribution of cation composition in perovskite films. The resultant p–i–n devices yielded a certified steady-state photon-to-electron conversion efficiency of 25.2% and durable stability. We added out-of-plane cations to homogenize the distribution of cations in perovskite films, resulting in a solar cell with improved efficiency and stability.

Metal halide perovskites of the general formula ABX 3 —where A is a monovalent cation such as caesium, methylammonium or formamidinium; B is divalent lead, tin or germanium; and X is a halide anion—have shown great potential as light harvesters for thin-film photovoltaics 1 – 5 . Among a large number of compositions investigated, the cubic α-phase of formamidinium lead triiodide (FAPbI 3 ) has emerged as the most promising semiconductor for highly efficient and stable perovskite solar cells 6 – 9 , and maximizing the performance of this material in such devices is of vital importance for the perovskite research community. Here we introduce an anion engineering concept that uses the pseudo-halide anion formate (HCOO − ) to suppress anion-vacancy defects that are present at grain boundaries and at the surface of the perovskite films and to augment the crystallinity of the films. The resulting solar cell devices attain a power conversion efficiency of 25.6 per cent (certified 25.2 per cent), have long-term operational stability (450 hours) and show intense electroluminescence with external quantum efficiencies of more than 10 per cent. Our findings provide a direct route to eliminate the most abundant and deleterious lattice defects present in metal halide perovskites, providing a facile access to solution-processable films with improved optoelectronic performance. Incorporation of the pseudo-halide anion formate during the fabrication of α-FAPbI 3 perovskite films eliminates deleterious iodide vacancies, yielding solar cell devices with a certified power conversion efficiency of 25.21 per cent and long-term operational stability.

The short exciton diffusion length associated with most classical organic semiconductors used in organic photovoltaics (5-20 nm) imposes severe limits on the maximum size of the donor and acceptor domains within the photoactive layer of the cell. Identifying materials that are able to transport excitons over longer distances can help advancing our understanding and lead to solar cells with higher efficiency. Here, we measure the exciton diffusion length in a wide range of nonfullerene acceptor molecules using two different experimental techniques based on photocurrent and ultrafast spectroscopy measurements. The acceptors exhibit balanced ambipolar charge transport and surprisingly long exciton diffusion lengths in the range of 20 to 47 nm. With the aid of quantum-chemical calculations, we are able to rationalize the exciton dynamics and draw basic chemical design rules, particularly on the importance of the end-group substituent on the crystal packing of nonfullerene acceptors. The short-range diffusion length of organic semiconductors severely limits exciton harvesting and charge generation in organic bulk heterojunction solar cells. Here, the authors report exciton diffusion length in the range of 20 to 47 nm for a wide range of non-fullerene acceptors molecules.

Non-fullerene acceptors based organic solar cells represent the frontier of the field, owing to both the materials and morphology manipulation innovations. Non-radiative recombination loss suppression and performance boosting are in the center of organic solar cell research. Here, we developed a non-monotonic intermediate state manipulation strategy for state-of-the-art organic solar cells by employing 1,3,5-trichlorobenzene as crystallization regulator, which optimizes the film crystallization process, regulates the self-organization of bulk-heterojunction in a non-monotonic manner, i.e., first enhancing and then relaxing the molecular aggregation. As a result, the excessive aggregation of non-fullerene acceptors is avoided and we have achieved efficient organic solar cells with reduced non-radiative recombination loss. In PM6:BTP-eC9 organic solar cell, our strategy successfully offers a record binary organic solar cell efficiency of 19.31% (18.93% certified) with very low non-radiative recombination loss of 0.190 eV. And lower non-radiative recombination loss of 0.168 eV is further achieved in PM1:BTP-eC9 organic solar cell (19.10% efficiency), giving great promise to future organic solar cell research. Non-radiative recombination loss suppression is critical for boosting performance of organic solar cells. Here, the authors regulate self-organization of bulk-heterojunction in a non-monotonic manner, and achieve device efficiency over 19% with low non-radiative recombination loss down to 0.168 eV.

Controlling the crystallinity and surface morphology of perovskite layers by methods such as solvent engineering 1 , 2 and methylammonium chloride addition 3 – 7 is an effective strategy for achieving high-efficiency perovskite solar cells. In particular, it is essential to deposit α-formamidinium lead iodide (FAPbI 3 ) perovskite thin films with few defects due to their excellent crystallinity and large grain size. Here we report the controlled crystallization of perovskite thin films with the combination of alkylammonium chlorides (RACl) added to FAPbI 3 . The δ-phase to α-phase transition of FAPbI 3 and the crystallization process and surface morphology of the perovskite thin films coated with RACl under various conditions were investigated through in situ grazing-incidence wide-angle X-ray diffraction and scanning electron microscopy. RACl added to the precursor solution was believed to be easily volatilized during coating and annealing owing to dissociation into RA 0 and HCl with deprotonation of RA + induced by RA⋯H + -Cl − binding to PbI 2 in FAPbI 3 . Thus, the type and amount of RACl determined the δ-phase to α-phase transition rate, crystallinity, preferred orientation and surface morphology of the final α-FAPbI 3 . The resulting perovskite thin layers facilitated the fabrication of perovskite solar cells with a power-conversion efficiency of 26.08% (certified 25.73%) under standard illumination. In situ grazing-incidence wide-angle X-ray diffraction and scanning electron microscopy were used to evaluate the crystallization process and surface morphology of perovskite thin films coated with alkylammonium chlorides, which were used to fabricate high-efficiency perovskite solar cells.

Driven by recent improvements in efficiency and stability of perovskite solar cells (PSCs), upscaling of PSCs has come to be regarded as the next step. Specifically, a high-throughput, low-cost roll-to-roll (R2R) processes would be a breakthrough to realize the commercialization of PSCs, with uniform formation of precursor wet film and complete conversion to perovskite phase via R2R-compatible processes necessary to accomplish this goal. Herein, we demonstrate the pilot-scale, fully R2R manufacturing of all the layers except for electrodes in PSCs. Tert-butyl alcohol (tBuOH) is introduced as an eco-friendly antisolvent with a wide processing window. Highly crystalline, uniform formamidinium (FA)-based perovskite formation via tBuOH:EA bathing was confirmed by achieving high power conversion efficiencies (PCEs) of 23.5% for glass-based spin-coated PSCs, and 19.1% for gravure-printed flexible PSCs. As an extended work, R2R gravure-printing and tBuOH:EA bathing resulted in the highest PCE reported for R2R-processed PSCs, 16.7% for PSCs with R2R-processed SnO 2 /FA-perovskite, and 13.8% for fully R2R-produced PSCs. Driven by recent improvement in efficiency and stability of perovskite solar cells, the next step toward commercialisation is upscaling. Here, the authors demonstrate pilot-scale fully roll-to-roll manufacturing of flexible perovskite solar cells through gravure-printing and antisolvent bathing.

Doping of perovskite semiconductors 1 and passivation of their grain boundaries 2 remain challenging but essential for advancing high-efficiency perovskite solar cells. Particularly, it is crucial to build perovskite/indium tin oxide (ITO) Schottky contact based inverted devices without predepositing a layer of hole-transport material 3 – 5 . Here we report a dimethylacridine-based molecular doping process used to construct a well-matched p -perovskite/ITO contact, along with all-round passivation of grain boundaries, achieving a certified power conversion efficiency (PCE) of 25.39%. The molecules are shown to be extruded from the precursor solution to the grain boundaries and the bottom of the film surface in the chlorobenzene-quenched crystallization process, which we call a molecule-extrusion process. The core coordination complex between the deprotonated phosphonic acid group of the molecule and lead polyiodide of perovskite is responsible for both mechanical absorption and electronic charge transfer, and leads to p -type doping of the perovskite film. We created an efficient device with a PCE of 25.86% (reverse scan) and that maintained 96.6% of initial PCE after 1,000 h of light soaking. A dimethylacridine-based molecular doping process is used to construct a well-matched p -perovskite/indium tin oxide contact, along with all-round passivation of grain boundaries, achieving a certified power conversion efficiency of 25.39%.

Incorporating mixed ion is a frequently used strategy to stabilize black-phase formamidinum lead iodide perovskite for high-efficiency solar cells. However, these devices commonly suffer from photoinduced phase segregation and humidity instability. Herein, we find that the underlying reason is that the mixed halide perovskites generally fail to grow into homogenous and high-crystalline film, due to the multiple pathways of crystal nucleation originating from various intermediate phases in the film-forming process. Therefore, we design a multifunctional fluorinated additive, which restrains the complicated intermediate phases and promotes orientated crystallization of α-phase of perovskite. Furthermore, the additives in-situ polymerize during the perovskite film formation and form a hydrogen-bonded network to stabilize α-phase. Remarkably, the polymerized additives endow a strongly hydrophobic effect to the bare perovskite film against liquid water for 5 min. The unencapsulated devices achieve 24.10% efficiency and maintain >95% of the initial efficiency for 1000 h under continuous sunlight soaking and for 2000 h at air ambient of ~50% humid, respectively. Formamidinum lead iodide perovskite solar cells commonly suffer from photoinduced phase segregation and humidity instability. Here, the authors design a multifunctional fluorinated additive to promote orientated crystallization of α-phase, and achieve maximum efficiency of 24.1% and T95 over 1000 h.

Two-dimensional (2D) and three-dimensional (3D) perovskite heterostructures have played a key role in advancing the performance of perovskite solar cells 1 , 2 . However, the migration of cations between 2D and 3D layers results in the disruption of octahedral networks, leading to degradation in performance over time 3 , 4 . We hypothesized that perovskitoids, with robust organic–inorganic networks enabled by edge- and face-sharing, could impede ion migration. We explored a set of perovskitoids of varying dimensionality and found that cation migration within perovskitoid–perovskite heterostructures was suppressed compared with the 2D–3D perovskite case. Increasing the dimensionality of perovskitoids improves charge transport when they are interfaced with 3D perovskite surfaces—this is the result of enhanced octahedral connectivity and out-of-plane orientation. The 2D perovskitoid (A6BfP) 8 Pb 7 I 22 (A6BfP: N -aminohexyl-benz[f]-phthalimide) provides efficient passivation of perovskite surfaces and enables uniform large-area perovskite films. Devices based on perovskitoid–perovskite heterostructures achieve a certified quasi-steady-state power conversion efficiency of 24.6% for centimetre-area perovskite solar cells. We removed the fragile hole transport layers and showed stable operation of the underlying perovskitoid–perovskite heterostructure at 85 °C for 1,250 h for encapsulated large-area devices in ambient air. We find that 2D–3D perovskitoid passivation applied to perovskite solar cells impedes cation migration and decreases carrier recombination at the interface, providing enhanced operating stability at elevated temperatures and increased power conversion efficiencies.

The open-circuit voltage ( V OC ) deficit in perovskite solar cells is greater in wide-bandgap (over 1.7 eV) cells than in perovskites of roughly 1.5 eV (refs.  1 , 2 ). Quasi-Fermi-level-splitting measurements show V OC -limiting recombination at the electron-transport-layer contact 3 – 5 . This, we find, stems from inhomogeneous surface potential and poor perovskite–electron transport layer energetic alignment. Common monoammonium surface treatments fail to address this; as an alternative, we introduce diammonium molecules to modify perovskite surface states and achieve a more uniform spatial distribution of surface potential. Using 1,3-propane diammonium, quasi-Fermi-level splitting increases by 90 meV, enabling 1.79 eV perovskite solar cells with a certified 1.33 V V OC and over 19% power conversion efficiency (PCE). Incorporating this layer into a monolithic all-perovskite tandem, we report a record V OC of 2.19 V (89% of the detailed balance V OC limit) and over 27% PCE (26.3% certified quasi-steady state). These tandems retained more than 86% of their initial PCE after 500 h of operation. Because open-circuit voltage deficit is greater in wide-bandgap perovskite solar cells, the authors introduce diammonium molecules to modify perovskite surface states and achieve a more uniform spatial distribution of surface potential, enabling record voltage all-perovskite tandem solar cells.