shuhui

The transport properties of double and triple cation perovskite have been explored by SSPG and SSPC, under various conditions. The addition of cesium has been shown to significantly enhance the diffusion length of the perovskite layers, this improvement being reversibly annihilated by a vacuum stress. This behavior can be explained considering the interaction between the iodine vacancies and oxygen.

In this study, the transport properties of high quality double and triple cation perovskite are explored under different environmental stresses by Steady State Photocurrent (SSPC) and Steady State Photocarrier Grating (SSPG) measurements. SSPG allows a direct measurement of the ambipolar diffusion length that is significantly higher for the cesium containing perovskite (1.4 micron compared to 0.57 micron for a double cation compound). This positive effect is shown to be reversibly annihilated as the samples are put under vacuum, and to be accelerated with the increase of the temperature. The degradation of the material properties appears together with the activation of a defect trap level and a rise of the doping level in the material. This behavior is discussed considering the interaction between the iodine vacancies contained in the perovskite and oxygen which is known to lead to trap passivation.

A facile passivation process is introduced to reduce the surface deep traps of Pb vacancy (V _Pb) and I interstitial (I _i) for CsPbI₂Br perovskite film. The dissociative Pb²⁺ in Pb(NO₃)₂ solution would combine with I _i (the excess I‐ions) and fill to V _pb of the perovskite surface, resulting in the less nonradiative recombination and defect states density of the perovskite film.

Cesium halide perovskite CsPbX₃ has emerged to be a promising candidate for photovoltaic materials due to their componential and thermal stability. During the fabrication of CsPbX₃ films, rich halide ions could cause deep trap states on the surface of the perovskite film, leading to much charge recombination. Herein, Pb²⁺ solution post‐processing strategy is introduced to passivate the deep trap states of CsPbI₂Br films. The dissociative Pb²⁺ in the solution effectively combines with the excess halide ions on the perovskite surface to reduce the deep trap states of Pb vacancy (V _Pb) and I interstitial (I _i). As a result, the average photoluminescence lifetimes τ _ave of the perovskite film prolonged nearly double after passivation. The trap density of perovskite is effectively decreased from 8 × 10¹⁶ to 6.64 × 10¹⁶ cm⁻³. The CsPb₂Br solar cell shows an open‐circuit‐voltage as high as 1.29 V and power conversion efficiency of 12.34% with small hysteresis. The postprocessing method would provide an avenue to improve further the efficiency of inorganic perovskite solar cells via reducing surface traps.

Atmospheric pressure spatial atomic layer technique (s‐ALD) has been adopted to introduce a ZnO buffer layer in the p‐i‐n planar perovskite solar cell architecture. The s‐ALD layer successfully prevents damages during ITO sputtering deposition, enabling the fabrication of efficient and stable semitransparent bifacial perovskite solar cells.

The replacement of the conventional top metal contact with a semi‐transparent conducting electrode such as sputtered indium‐tin oxide (ITO) is strictly required to adopt the perovskite solar cell (PSC) in hybrid tandem photovoltaic applications. In order to prevent sputtering damages on the perovskite absorber and the organic materials adopted in p‐i‐n planar architecture, an atmospheric pressure spatial atomic layer deposited (s‐ALD) ZnO buffer layer has been included. The use of a 45 nm thick s‐ALD layer enables the fabrication of a PSC with a power conversion efficiency (PCE) of 14.7%, with a similar PCE when illuminated from the ITO/s‐ALD ZnO side. When adopted in a four terminal configuration with a c‐Si solar cell (PCE of 18.6%), a 2.5% absolute PCE gain is observed with respect to the stand alone c‐Si. Finally, the semi‐transparent PSC shows an excellent shelf life, and only −4% degradation on the tracked maximum power point when encapsulated and aged at 65 °C in an inert atmosphere after 1500 h.

Carboxyl‐substituted perylene (PTCA) has been successfully applied as the electron‐transport layer in perovskite solar cells. By the carboxyl groups, PTCA can effectively connect the perovskite layer and FTO, thus reducing the interface barriers induced by weak contact, resulting in a high PCE of 16.09%. In addition, the PTCA‐based devices exhibit remarkable stability under illumination in ambient conditions without encapsulation.

Carboxyl‐substituted perylene (PTCA) has been successfully applied as the electron‐transport layer in perovskite solar cells. The large rigid π–π conjugated plane structure in PTCA endows it excellent electronic transmission performance. By the carboxyl groups, PTCA can effectively connect the perovskite layer and FTO, thus reducing the interface barriers induced by weak contact, resulting in a high PCE of 16.09%. In addition, the PTCA‐based devices exhibit remarkable stability under illumination in ambient conditions without encapsulation.

Atmospheric pressure spatial atomic layer technique (s‐ALD) has been adopted to introduce a ZnO buffer layer in the p‐i‐n planar perovskite solar cell architecture. The s‐ALD layer successfully prevents damages during ITO sputtering deposition, enabling the fabrication of efficient and stable semitransparent bifacial perovskite solar cells.

The replacement of the conventional top metal contact with a semi‐transparent conducting electrode such as sputtered indium‐tin oxide (ITO) is strictly required to adopt the perovskite solar cell (PSC) in hybrid tandem photovoltaic applications. In order to prevent sputtering damages on the perovskite absorber and the organic materials adopted in p‐i‐n planar architecture, an atmospheric pressure spatial atomic layer deposited (s‐ALD) ZnO buffer layer has been included. The use of a 45 nm thick s‐ALD layer enables the fabrication of a PSC with a power conversion efficiency (PCE) of 14.7%, with a similar PCE when illuminated from the ITO/s‐ALD ZnO side. When adopted in a four terminal configuration with a c‐Si solar cell (PCE of 18.6%), a 2.5% absolute PCE gain is observed with respect to the stand alone c‐Si. Finally, the semi‐transparent PSC shows an excellent shelf life, and only −4% degradation on the tracked maximum power point when encapsulated and aged at 65 °C in an inert atmosphere after 1500 h.

A simple Ti cathode interlayer is incorporated in planar structure perovskite solar cells. The Ti interlayer is able to improve the uniformity of top metal electrode layer. In addition, a Ti‐N bonding layer is formed at the Ti/perovskite interface, which passivates the traps at perovskite surface, resulting in a decent power conversion efficiency of 18.1%.

Electron and hole transport layers play a critical role in high performance metal halide perovskite solar cells. Many organic and inorganic electron/hole transport layers are developed and studied in the last few years. In this work, the authors innovatively use a ultra‐thin layer of titanium (Ti) as a cathode interlayer between metal electrode and perovskite film, without using any organic or inorganic electron transport layers, in planar heterojunction perovskite solar cells. X‐ray photoelectron spectroscopy and soft X‐ray absorption near edge structure results prove that Ti film forms a bonding layer with nitrogen (N) atoms in metylammonium anions at perovskite/Ti interface, which passivates surface defects and suppresses surface decomposition of perovskite film. The champian solar cell based on methylammonium lead iodide (CH₃NH₃PbI₃) shows a short circuit current density of 22.5 mA cm⁻², a open circuit voltage of 1.03 V and a fill factor of 78.2%, yielding a power conversion efficiency of 18.1%. Notably, Ti has low diffusivity and serves as a compact blocking layer that prevents the diffusion of metal atoms into the perovskite layer, resulting in improved device stability. Our work shows that Ti is a promising low‐cost material to replace organic and inorganic electron transporting layers for efficient perovskite solar cells.

Anode contact engineering of p‐i‐n type perovskite solar cells is demonstrated. With the control of the interfacial properties using an ultrathin metallic layer and an insulating layer, a high V _oc of 1.15 V and a power conversion efficiency of 19.3% are obtained. Furthermore, a substrate‐type device with an extremely high V _oc of 1.18 V is also demonstrated.

With photocurrents in perovskite solar cells close to their practical limit, it is imperative to improve their open‐circuit voltage to go beyond a loss‐in‐potential less than 100 mV. However, state‐of‐the‐art p‐i‐n perovskite solar cells are reported with a V _oc of around 1.1–1.5 V, limiting their efficiency improvement. Herein, the authors demonstrate that the V _oc of p‐i‐n perovskite solar cells can be successfully improved via anode contact engineering. First of all, by introducing a partially oxidized nickel layer, the authors are able to remove the potential barrier for hole transport and enhance the crystallinity of the hole transporting layer, both of which are believed to contribute to the V _oc and FF improvement. Furthermore, by separating the inorganic NiMgO_x hole transporting layer from the perovskite absorbing layer with a poly(4‐vinylpyridine) (PVP) insulating layer, the interfacial recombination could be effectively suppressed, the V _oc climbs to an impressive value of 1.15 V along with a power conversion efficiency of 19.3%. Finally, a substrate‐type perovskite solar cell is fabricated with an extremely high V _oc of 1.18 V, representing a very low voltage deficit in the p‐i‐n perovskite solar cells. Our works provide an avenue for further reducing the loss‐in‐potential of perovskite solar cells.

The lattice of inorganic CsPbBr₃ halide is modulated by doping alkali metal cations to form Cs_1−x R _x PbBr₃ (R = Li, Na, K, Rb, x = 0–1) perovskites. Through tuning R/Cs ratio, a PCE up to 9.86% and improved stability in 80% humidity are achieved for HTL‐free Cs_0.91Rb_0.09PbBr₃ solar cell.

Abstract

The crystal structure of cesium lead halide (CsPbX₃, X = I, Br, Cl) determines its charge‐carrier trap state and solar‐to‐electrical conversion ability in inorganic perovskite solar cells (PSCs). Here, the compositional engineering of inorganic CsPbBr₃ perovskite by means of doping with various alkali metal cations is studied. The lattice dimensions and energy levels of Cs_1‐x R _x PbBr₃ (R = Li, Na, K, Rb, x = 0–1) halides are optimized by tuning Cs/R ratio. Arising from promoting effects of alkali metal cations doped perovskite halides such as lattice shrink, crystallized dynamics, and electrical‐energy distribution, a maximum power conversion efficiency as high as 9.86% is achieved for hole transporting layer‐free Cs_0.91Rb_0.09PbBr₃ tailored solar cell owing to the suppressed non‐radiative losses and radiative recombination. Furthermore, the all‐inorganic Cs_0.91Rb_0.09PbBr₃ solar cell without encapsulation remains 97% of initial efficiency when suffering persistent attack by 80% RH in air atmosphere over 700 h, which is in comparable with state‐of‐the‐art organic–inorganic hybrid and all‐inorganic PSC devices. Employing alkali metal cations to modulate perovskite layers provide new opportunities of making high‐performance inorganic PSC platforms.

Efficiency, stability, and the cost of fabrication are the three edges of the triangle that represents the commercialization of perovskite solar cells. Overcoming the cell's stability against heat, light, and humidity is a key challenge for scalability.

Abstract

The discovery and development of organic–inorganic halide perovskites with exceptional properties has become an active research area in the field of photovoltaics. Perovskite solar cells (PSCs) have attracted much attention in recent years due to various attractive advantages, such as simple solution processing, low manufacturing cost, and high performances with power conversion efficiencies now reaching certified values close to 23% within a very short time frame of five years. Despite this rapid progress, the inferior device stability remains a great challenge. This review focuses on the factors limiting the stability of PSCs, such as humidity, heat, and irradiation, summarizing recent strategies to overcome stability and fabrication obstacles in order to open new perspectives to achieve highly durable perovskite devices toward future industrialization.

Understanding how excess lead iodide precursor improves halide perovskite solar cell performance

Understanding how excess lead iodide precursor improves halide perovskite solar cell performance, Published online: 17 August 2018; doi:10.1038/s41467-018-05583-w