Chen Weijie

Carrier transport in methylammonium lead iodide (MAPbI₃)-based hybrid organic–inorganic perovskites (HOIPs) is obscured by vacancy-mediated ion migration. Thus, the nature of migrating species (cation/anion) and their effect on electronic transport in MAPbI₃ has remained controversial. Temperature-dependent pulsed voltage–current measurements of MAPbI₃ thin films are performed under dark conditions, designed to decouple ion-migration/accumulation and electronic transport. Measurement conditions (electric-field history and scan rate) are shown to affect the electronic transport in MAPbI₃ thin films, through a mechanism involving ion migration and accumulation at the electrode interfaces. The presence of thermally activated processes with distinct activation energies (E_a) of 0.1 ± 0.001 and 0.41 ± 0.02 eV is established, and are assigned to electromigration of iodine vacancies and methylammonium vacancies, respectively. Analysis of activation energies obtained from electronic conduction versus capacitive discharge shows that the electromigration of these ionic species is responsible for the modification of interfacial electronic properties of MAPbI₃, and elaborates previously unaddressed issues of “fast” and “slow” ion migration. The results demonstrate that the intrinsic behavior of MAPbI₃ material is responsible for the hysteresis of the solar cells, but also have implications for other HOIP-based devices, such as memristors, detectors, and energy storage devices.

It is demonstrated that hybrid perovskite (MAPbI₃)-based M–S–M devices show I–V anomalies (hysteresis and field/scan rate dependent dynamic rectification) even under dark conditions. Using temperature-dependent pulsed current–voltage measurements, the origin of such I–V anomalies in migration and accumulation of two ionic species with different activation energies (0.1 and 0.41 eV) is established.

Semitransparent perovskite solar cells (PSCs) are of interest for application in tandem solar cells and building-integrated photovoltaics. Unfortunately, several perovskites decompose when exposed to moisture or elevated temperatures. Concomitantly, metal electrodes can be degraded by the corrosive decomposition products of the perovskite. This is even the more problematic for semitransparent PSCs, in which the semitransparent top electrode is based on ultrathin metal films. Here, we demonstrate outstandingly robust PSCs with semitransparent top electrodes, where an ultrathin Ag layer is sandwiched between SnO_x grown by low-temperature atomic layer deposition. The SnO_x forms an electrically conductive permeation barrier, which protects both the perovskite and the ultrathin silver electrode against the detrimental impact of moisture. At the same time, the SnO_x cladding layer underneath the ultra-thin Ag layer shields the metal against corrosive halide compounds leaking out of the perovskite. Our semitransparent PSCs show an efficiency higher than 11% along with about 70% average transmittance in the near-infrared region (λ > 800 nm) and an average transmittance of 29% for λ = 400–900 nm. The devices reveal an astonishing stability over more than 4500 hours regardless if they are exposed to ambient atmosphere or to elevated temperatures.

SnO_x/Ag/SnO_x-based semitransparent electrodes are used to prepare self-encapsulated semitransparent perovskite solar cells, in which the SnO_x grown by atomic layer deposition serves as a permeation barrier. The semitransparent cells show an efficiency of 11.8% and 29% average transmittance between 400 and 900 nm, realizing an outstanding stability over more than 4500 h in ambient air and at elevated temperatures.

PEDOT:PSS suffers from its poor structural homogeneity. In article number 1601499, Yuan Li, Xueqing Qiu, Hin-Lap Yip, and co-workers report a novel PEDOT:MNSF with enhanced structural homogeneity and promising performance in organic electronic devices. The branched structure of PEDOT:MNSF contributes to its hole extract property and the herringbone image arranged by ladybug indicates that this design concept will move PEDOT-based materials toward a brilliant future.