Electrochemical Deposition of CsPbBr3 Perovskite for Photovoltaic Devices with Robust Ambient Stability.

Alkali halide perovskites have emerged as representative candidates for novel opto-electronic devices owing to their balanced efficiency and stability. However, their fabrication method still remains a challenging topic with conflicts among their effectiveness, complexity, and cost. Herein, a complete two-step electrochemical method has been applied in the fabrication of inorganic perovskites for the first time. The dimension and microstructure of CsPbBr3 can be easily controlled by variation of simple physical parameters during the fabrication. By optimizing the parameters, high-quality CsPbBr3 films are obtained, and the champion device has achieved an efficiency of 7.86% with a high open-circuit voltage of 1.43 V. More importantly, the as-fabricated materials have shown an extraordinary robust stability against environmental conditions even after 150 days of exposure to air without encapsulation. This has evidently proved the electrochemical methods as an effective route for perovskite synthesis in its future development.

Hierarchy of interfacial passivation in inverted perovskite solar cells.

The crucial hierarchy of the interfacial passivation at different positions of perovskite solar cells together with the corresponding mechanism has been studied despite the selection of passivation mediums in this work. The passivation on the upper interface could more effectively enhance the device performance with an efficiency of 19.55% compared to the pristine and lower passivated cells (15.90% and 18.39%, respectively). Furthermore, the upper passivated devices exhibit better long-term and thermal stability than the lower passivated and pristine ones.

Elegant Face-Down Liquid-Space-Restricted Deposition of CsPbBr3 Films for Efficient Carbon-Based All-Inorganic Planar Perovskite Solar Cells.

It is a great challenge to obtain the uniform films of bromide-rich perovskites such as CsPbBr3 in the two-step sequential solution process (two-step method), which was mainly due to the decomposition of the precursor films in solution. Herein, we demonstrated a novel and elegant face-down liquid-space-restricted deposition to inhibit the decomposition and fabricate high-quality CsPbBr3 perovskite films. This method is highly reproducible, and the surface of the films was smooth and uniform with an average grain size of 860 nm. As a consequence, the planar perovskite solar cells (PSCs) without the hole-transport layer based on CsPbBr3 and carbon electrodes exhibit enhanced power conversion efficiency (PCE) along with high open circuit voltage ( VOC). The champion device has achieved a PCE of 5.86% with a VOC of 1.34 V, which to our knowledge is the highest performing CsPbBr3 PSC in planar structure. Our results suggest an efficient and low-cost route to fabricate the high-quality planar all-inorganic PSCs.

PbI2 heterogeneous-cap-induced crystallization for an efficient CH3NH3PbI3 layer in perovskite solar cells.

PbI2 heterogeneous-cap-induced crystallization with a face-to-face configuration is proposed to obtain efficient CH3NH3PbI3 perovskite films during thermal annealing. The films with large-size and dominative (110)-oriented grains can effectively boost the photovoltaic performance of the perovskite solar cells.

Facile Face-Down Annealing Triggered Remarkable Texture Development in CH3NH3PbI3 Films for High-Performance Perovskite Solar Cells.

Herein, we demonstrate that the facile face-down annealing route which effectively confines the evaporation of residual solvent molecules in one-step deposited precursor films can controllably enable the formation of (110) textured CH3NH3PbI3 films consisting of high-crystallinity well-ordered micrometer-sized grains that span vertically the entire film thickness. Such microstructural features dramatically decrease nonradiative recombination sites as well as greatly improve the transport property of charge carries in the films compared with that of the nontextured ones obtained by the conventional annealing route. As a consequence, the planar-heterojunction perovskite solar cells with these textured CH3NH3PbI3 films exhibit significantly enhanced power conversion efficiency (PCE) along with small hysteresis and excellent stability. The champion cell yields impressive PCE boosting to 18.64% and a stabilized value of around 17.22%. Particularly, it can maintain 86% of its initial value after storage for 20 days in ambient conditions with relative humidity of 10-20%. Our work suggests a facile and effective route for further boosting the efficiency and stability of low-cost perovskite solar cells.

Highly Flexible Self-Powered Organolead Trihalide Perovskite Photodetectors with Gold Nanowire Networks as Transparent Electrodes.

Organolead trihalide perovskites (OTPs) such as CH3NH3PbI3 (MAPbI3) have attracted much attention as the absorbing layer in solar cells and photodetectors (PDs). Flexible OTP devices have also been developed. Transparent electrodes (TEs) with higher conductivity, stability, and flexibility are necessary to improve the performance and flexibility of flexible OTP devices. In this work, patterned Au nanowire (AuNW) networks with high conductivity and stability are prepared and used as TEs in self-powered flexible MAPbI3 PDs. These flexible PDs show peak external quantum efficiency and responsivity of 60% and 321 mA/W, which are comparable to those of MAPbI3 PDs based on ITO TEs. The linear dynamic range and response time of the AuNW-based flexible PDs reach ∼84 dB and ∼4 µs, respectively. Moreover, they show higher flexibility than ITO-based devices, around 90%, and 60% of the initial photocurrent can be retained for the AuNW-based flexible PDs when bent to radii of 2.5 and 1.5 mm. This work suggests a high-performance, highly flexible, and stable TE for OTP flexible devices.

Coarsening of one-step deposited organolead triiodide perovskite films via Ostwald ripening for high efficiency planar-heterojunction solar cells.

Large organolead triiodide perovskite (OTP) grains with little intragranular defects are beneficial to minimize carrier recombination, hence boosting cell performance. However, OTP films deposited by the widely used one-step spin-coating route are usually composed of small grains, because the poor thermal stability of OTP inherently restricts the processing window (temperature, time) during the film preparation, thus limiting grain coarsening in the film. Herein, the remarkable grain coarsening via Ostwald ripening in one-step deposited OTP films has been successfully realized by a facile and effective post-synthesis high-temperature heating treatment assisted with spin-coated CH3NH3I. By systematically investigating the heating treatment parameters, a high-quality OTP film with an enlarged average grain size from ∼280 nm to 1.2 µm, greatly enhanced crystallinity, and excellent stoichiometry is achieved. Benefiting from such improved features, this modified film shows significantly reduced defect states corresponding to the decrease of recombination centers, as well as enhanced carrier transport and injection properties, which lead to the dramatically boosted efficiency from 14.54% to 16.88% for planar-heterojunction solar cells. More importantly, the improved OTP film quality provides the possibility of thickening the absorber layer of cells to realize more sufficient absorption without serious aggravation of charge recombination. By further optimizing the thickness of the coarsened OTP films, highly efficient cells with relatively excellent reproducibility and an optimal efficiency of 19.24% are achieved.

Laser-assisted crystallization of CH3NH3PbI3 films for efficient perovskite solar cells with a high open-circuit voltage.

Laser irradiation as a rapid crystallization approach was successfully introduced to prepare homogeneous, dense-grained CH3NH3PbI3 films. Planar-heterojunction solar cells employing these high-quality films showed the optimal efficiency of 17.8% with a remarkably high open-circuit voltage of 1.146 V.