High efficiency perovskite solar cells were fabricated reproducibly via Lewis base adduct of lead(II) iodide. PbI2 was dissolved in N,N-dimethyformamide with equimolar N,N-dimethyl sulfoxide (DMSO) and CH3NH3I. Stretching vibration of S═O appeared at 1045 cm(-1) for bare DMSO, which was shifted to 1020 and 1015 cm(-1) upon reacting DMSO with PbI2 and PbI2 + CH3NH3I, respectively, indicative of forming the adduct of PbI2·DMSO and CH3NH3I·PbI2·DMSO due to interaction between Lewis base DMSO and/or iodide (I(-)) and Lewis acid PbI2. Spin-coating of a DMF solution containing PbI2, CH3NH3I, and DMSO (1:1:1 mol %) formed a transparent adduct film, which was converted to a dark brown film upon heating at low temperature of 65 °C for 1 min due to removal of the volatile DMSO from the adduct. The adduct-induced CH3NH3PbI3 exhibited high charge extraction characteristics with hole mobility as high as 3.9 × 10(-3) cm(2)/(V s) and slow recombination rate. Average power conversion efficiency (PCE) of 18.3% was achieved from 41 cells and the best PCE of 19.7% was attained via adduct approach.

Key insights into the evolution of lithium-ion batteries: present, future, and hybridized technologies.

Medical X-ray imaging procedures require digital flat detectors operating at low doses to reduce radiation health risks. Solution-processed organic-inorganic hybrid perovskites have characteristics that make them good candidates for the photoconductive layer of such sensitive detectors. However, such detectors have not yet been built on thin-film transistor arrays because it has been difficult to prepare thick perovskite films (more than a few hundred micrometres) over large areas (a detector is typically 50 centimetres by 50 centimetres). We report here an all-solution-based (in contrast to conventional vacuum processing) synthetic route to producing printable polycrystalline perovskites with sharply faceted large grains having morphologies and optoelectronic properties comparable to those of single crystals. High sensitivities of up to 11 microcoulombs per air KERMA of milligray per square centimetre (μC mGy cm) are achieved under irradiation with a 100-kilovolt bremsstrahlung source, which are at least one order of magnitude higher than the sensitivities achieved with currently used amorphous selenium or thallium-doped cesium iodide detectors. We demonstrate X-ray imaging in a conventional thin-film transistor substrate by embedding an 830-micrometre-thick perovskite film and an additional two interlayers of polymer/perovskite composites to provide conformal interfaces between perovskite films and electrodes that control dark currents and temporal charge carrier transportation. Such an all-solution-based perovskite detector could enable low-dose X-ray imaging, and could also be used in photoconductive devices for radiation imaging, sensing and energy harvesting.

Organic-inorganic halide perovskite is believed to be a potential candidate for high efficiency solar cells because power conversion efficiency (PCE) was certified to be more than 22%. Nevertheless, mismatch of PCE due to current density (J)-voltage (V) hysteresis in perovskite solar cells is an obstacle to overcome. There has been much lively debate on the origin of J-V hysteresis; however, effective methodology to solve the hysteric problem has not been developed. Here we report a universal approach for hysteresis-free perovskite solar cells via defect engineering. A severe hysteresis observed from the normal mesoscopic structure employing TiO and spiro-MeOTAD is almost removed or does not exist upon doping the pure perovskites, CHNHPbI and HC(NH)PbI, and the mixed cation/anion perovskites, FAMAPbIBr and FAMACsPbIBr, with potassium iodide. Substantial reductions in low-frequency capacitance and bulk trap density are measured from the KI-doped perovskite, which is indicative of trap-hysteresis correlation. A series of experiments with alkali metal iodides of LiI, NaI, KI, RbI and CsI reveals that potassium ion is the right element for hysteresis-free perovskite. Theoretical studies suggest that the atomistic origin of the hysteresis of perovskite solar cells is not the migration of iodide vacancy but results from the formation of iodide Frenkel defect. Potassium ion is able to prevent the formation of Frenkel defect since K energetically prefers the interstitial site. A complete removal of hysteresis is more pronounced at mixed perovskite system as compared to pure perovskites, which is explained by lower formation energy of K interstitial (-0.65 V for CHNHPbI vs -1.17 V for mixed perovskite). The developed KI doping methodology is universally adapted for hysteresis-free perovskite regardless of perovskite composition and device structure.

A perovskite solar cell based on ZnO nanorods was prepared, and its photovoltaic performance was investigated. ZnO nanorods were grown on the ZnO seed layer from solution, and their diameters and lengths were controlled by precursor concentration and growth time. CH3NH3PbI3 perovskite infiltrated ZnO nanorods showed a power conversion efficiency of 11.13% with short-circuit current density J sc of 20.08 mA/cm2, open-circuit voltage V oc of 991 mV and fill factor of 0.56. Square spectral feature of external quantum efficiency (EQE) was observed, where EQE exceeded 80% in almost the entire wavelength range from 400 to 750 nm, and the integrated current density of 20.03 mA/cm2 calculated from EQE data was in good agreement with the observed J sc. Compared to the perfect spectral response of ZnO nanorods, a perovskite solar cell based on TiO2 nanorods exhibited an integrated current density (16 mA/cm2) much lower than the measured J sc (20.9 mA/cm2). In addition, time-limited photocurrent response under 530 and 700 nm monochromatic beams at 10 Hz showed that device signal amplitude, associated with charge collection, was rapidly saturated for the ZnO nanorod-based device whereas charge collection was not fully detected for the TiO2 nanorod-based device because of slow collection rate. The current results suggest that ZnO nanorod is an effective charge collection system in CH3NH3PbI3 based perovskite solar cells.