The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in by up to 100 millivolts. We achieved a high of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

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The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium and formamidinium mixed cations. Currently, high-quality mixed-cation perovskite thin films are normally made by use of antisolvent protocols. However, the widely used "antisolvent"-assisted fabrication route suffers from challenges such as poor device reproducibility, toxic and hazardous organic solvent, and incompatibility with scalable fabrication process. Here, a simple dual-source precursor approach is developed to fabricate high-quality and mirror-like mixed-cation perovskite thin films without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible current density-voltage hysteresis. A stabilized power output approaching 20% is obtained at the maximum power point. These results shed light on fabricating highly efficient perovskite solar cells via a simple process, and pave the way for solar cell fabrication via scalable methods in the near future.

The performance of perovskite photovoltaics is fundamentally impeded by the presence of undesirable defects that contribute to non-radiative losses within the devices. Although mitigating these losses has been extensively reported by numerous passivation strategies, a detailed understanding of loss origins within the devices remains elusive. Here, we demonstrate that the defect capturing probability estimated by the capture cross-section is decreased by varying the dielectric response, producing the dielectric screening effect in the perovskite. The resulting perovskites also show reduced surface recombination and a weaker electron-phonon coupling. All of these boost the power conversion efficiency to 22.3% for an inverted perovskite photovoltaic device with a high open-circuit voltage of 1.25 V and a low voltage deficit of 0.37 V (a bandgap ~1.62 eV). Our results provide not only an in-depth understanding of the carrier capture processes in perovskites, but also a promising pathway for realizing highly efficient devices via dielectric regulation.

I − ) can be exchanged by bromide (Br − ), [14] to deliver mixed-cation lead mixed-halide perovskite. The devices with the optimized perovskite have been proven to remarkable stability and impressive power conversion efficiency (PCE). [13,15,16] The precursor solution of mixed-cation lead mixed-halide perovskite is featured with colloidal chemistry, where it has soft coordination complex of [PbI 6 ] 4− cages with organic cations. [17,18] Coupled with complex crystallization process, the resulting perovskite films could induce inhomogeneous composition distribution and local unreacted species in bulk materials and/or at the surface. [19,20] Typically, the unreacted PbI 2 has been found to be present within the perovskite film, [21] which has positive impact on improving device performance through passivation roles. [22][23][24][25][26] For the organic-halide species, evidences suggest that there were some unreacted formamidinium iodide (FAI) species existing throughout the perovskite film, [19,21] exhibiting a FAI-rich region close to the surface of the perovskite film. Such FAI species normally cause the reduction in device performance owing to increase in ionic defects. Moreover, Snaith et al. [27] proposed unreacted ions (iodide or MA) throughout the film may accelerate the hysteresis effect by ion migrations. Similarly, Jacobsson et al. [21] found that the accumulation of unreacted organic-halide species in the grain boundaries would hinder the charge-carrier transportation Metal halide perovskite films are endowed with the nature of ions and polycrystallinity. Formamidinium iodide (FAI)-based perovskite films, which include large cations (FA) incorporated into the crystal lattice, are most likely to induce local defects due to the presence of the unreacted FAI species. Here, a diboron-assisted strategy is demonstrated to control the defects induced by the unreacted FAI both inside the grain boundaries and at the surface regions. The diboron compound (C 12 H 10 B 2 O 4 ) can selectively react with unreacted FAI, leading to reduced defect densities. Nonradiative recombination between a perovskite film and a hole-extraction layer is mitigated considerably after the introduction of the proposed approach and charge-carrier extraction is improved as well. A champion power conversion efficiency of 21.11% is therefore obtained with a stabilized power output of 20.83% at the maximum power point for planar perovskite solar cells. The optimized device also delivers negligible hysteresis effect under various scanning conditions. This approach paves a new way for mitigating defects and improving device performance. Perovskite Solar CellsPerovskite solar cells (PSCs) have inspired burgeoning interests for making skyrocketing revolution in new type photovoltaic field, [1][2][3][4][5][6][7][8][9] because of their excellent photovoltaic and optoelectronic properties. [10] Most of the reported perovskites are lead (Pb)-based materials in the form of APbX 3 , where A is organic cation CH 3 NH 3 + (MA) and X is halide anion iodi...

In many optoelectronic applications, patterning is required for functional and/or aesthetic purposes. However, established photolithographic technique cannot be applied directly to the hybrid perovskites, which are considered as promising candidates for optoelectronic applications. In this work, a wettability-assisted photolithography (WAP) process, which employs photolithography and one-step solution process to deposit hybrid perovskite, was developed for fabricating patterned hybrid perovskite films. Uniform pinhole-free hybrid perovskite films with sharp-edged micropatterns of any shapes can be constructed through the WAP process. Semitransparent solar cells with an adjustable active layer average visible transmittance of a wide range from 20.0% to 100% and regular solar cells based on patterned CHNHPbI perovskite films were fabricated to demonstrate that the WAP process was compatible with the manufacturing process of optoelectronic devices. With the widely equipped photolithographic facilities in the modern semiconductor industry, we believe the WAP process have a great potential in the industrial production of functionally or aesthetically patterned hybrid perovskite devices.

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Owing to straightforward stoichiometry-bandgap tunability, mixed-halide perovskites are ideal for many optoelectronic devices. However, unwanted halide segregation under operational conditions, including light illumination and voltage bias, restricts practical use. Additionally, the origin of voltageinduced halide segregation is still unclear. Herein, a systematic voltage threshold study in mixed bromide/iodide perovskite devices is performed and leads to observation of three distinct voltage thresholds corresponding to the doping of the hole transport material (0.7 ± 0.1 V), halide segregation (0.95 ± 0.05 V), and degradation (1.15 ± 0.05 V) for an optically stable mixed-halide perovskite composition with a low bromide content (10%). These empirical threshold voltages are minimally affected by composition until very Br-rich compositions, which reveals the dominant role of iodide/triiodide/iodine electrochemistry in voltage-induced Br/I phase separation and transport layer doping reactions in halide perovskite devices.