Zhiwen Jin

ITIC surface modification to achieve synergistic electron transport layer enhancement for planar-type perovskite solar cells with efficiency exceeding 20%

The electron transport layer (ETL), which also serves as the hole-blocking layer, is a key component in planar perovskite solar cells (PSCs). The commonly used ETL is an anatase-TiO2 (an-TiO2) film due to its excellent optical transmittance, chemical stability and semiconducting characteristics. Nevertheless, its rough surface and plenty of surface defects often lead to a substandard perovskite film and large J–V hysteresis. Herein, a novel low-trap-density ETL is developed by surface modification of the an-TiO2 film using small-molecular ITIC. As a result, the device efficiency has been dramatically increased from 17.12% to 20.08%, entering the league of the highest planar-type perovskite cells. Moreover, the J–V hysteresis has been significantly reduced. Further investigation shows that the ITIC smoothens the TiO2 surface, passivates defects or dangling bands parasitizing the TiO2 surface, and optimizes the device band alignment. In addition, it is demonstrated that the thin ITIC promotes the formation of high quality, uniform perovskite films with better surface coverage and large grain size, implying that there is a synergistic effect between the low-trap-density ITIC and high-mobility TiO2 in improved PSC performance.

All-Ambient Processed Binary CsPbBr3–CsPb2Br5 Perovskites with Synergistic Enhancement for High-Efficiency Cs–Pb–Br-Based Solar Cells

All-inorganic CsPbBr3 perovskite solar cells display outstanding stability toward moisture, light soaking, and thermal stressing, demonstrating great potential in tandem solar cells and toward commercialization. Unfortunately, it is still challenging to prepare high-performance CsPbBr3 films at moderate temperatures. Herein, a uniform, compact CsPbBr3 film was fabricated using its quantum dot (QD)-based ink precursor. The film was then treated using thiocyanate ethyl acetate (EA) solution in all-ambient conditions to produce a superior CsPbBr3-CsPb2Br5 composite film with a larger grain size and minimal defects. The achievement was attributed to the surface dissolution and recrystallization of the existing SCN- and EA. More specifically, the SCN- ions were first absorbed on the Pb atoms, leading to the dissolution and stripping of Cs+ and Br- ions from the CsPbBr3 QDs. On the other hand, the EA solution enhances the diffusion dynamics of surface atoms and the surfactant species. It is found that a small amount of CsPb2Br5 in the composite film gives the best surface passivation, while the Br-rich surface decreases Br vacancies (VBr) for a prolonged carrier lifetime. As a result, the fabricated device gives a higher solar cell efficiency of 6.81% with an outstanding long-term stability.

High-performance transparent ultraviolet photodetectors based on inorganic perovskite CsPbCl3 nanocrystals

Inorganic lead halide perovskite nanocrystals (CsPbCl3 NCs) with excellent ultraviolet (UV) light absorption, high carrier mobility, long carrier diffusion lengths, and long-term stability are good candidates as smart materials for transparent optoelectronic devices. In this study, transparent UV photodetectors (PDs) based on CsPbCl3 NCs were fabricated for the first time. The optimized device exhibited visible light transmittance approximately 90%, strong absorption of UV light in the wavelength from 300 nm to 410 nm, good photoresponsivity (1.89 A W−1), and a high on/off ratio (up to 103). Meanwhile, the rise and decay response times of the device were less than 41 ms and 43 ms, respectively. Furthermore, we performed detailed analysis of the effects by employing CsPbCl3 NCs in assembled films and final devices using various characterization methods. The simple fabrication and remarkable UV photodetection capabilities of CsPbCl3 NCs make them promising semiconducting candidates in optoelectronic applications.

CsPbCl3-Driven Low-Trap-Density Perovskite Grain Growth for >20% Solar Cell Efficiency

Abstract Charge recombination in grain boundaries is a significant loss mechanism for perovskite (PVK) solar cells. Here, a new strategy is demonstrated to effectively passivate trap states at the grain boundaries. By introducing a thin layer of CsPbCl3 coating before the PVK deposition, a passivating layer of PbI2 is formed at the grain boundaries. It is found that at elevated temperature, Cl− ions in the CsPbCl3 may migrate into the PVK via grain boundaries, reacting with MA+ to form volatile MACl and leaving a surface layer of PbI2 at the grain boundary. Further study confirms that there is indeed a small amount of PbI2 distributed throughout the grain boundaries, resulting in increased photoluminescence intensity, increased carrier lifetime, and decreased trap state density. It is also found that the process passivates only grain surfaces, with no observable effect on the morphology of the PVK thin film. Upon optimization, the obtained PVK‐film‐based solar cell delivers a high efficiency of 20.09% with reduced hysteresis and excellent stability.

Single-crystalline perovskite wafers with a Cr blocking layer for broad and stable light detection in a harsh environment

Herein, ultrathin (∼35 μm) CH3NH3PbI3 (MAPbI3) single-crystalline wafers have been successfully prepared by using an appropriate geometry-regulated dynamic-flow reaction system. The measurement results proved that the obtained wafers have high crystallinity, and showed broad light absorption from ultraviolet to near infrared (850 nm) which can be attributed to the indirect bandgap. Straight after, such an MAPbI3 wafer was used to fabricate high-quality photodetectors (PDs). On account of its faster carrier transport and significantly reduced defect density, the device exhibits a high photoresponse (R) of 5 A/W and short on/off response (0.039 s/0.017 s). Interestingly, by introducing a Cr interlayer between the MAPbI3 wafer and the Au electrode to avoid the migration of Au, the PD shows nearly no degradation when it works at 200 °C. Furthermore, the device performance shows very little degradation over the course of 60 days of storage under ambient conditions owing to its lack of grain boundaries. We believe the strategy reported here is very promising for achieving broad photodetection in a harsh environment.

All-inorganic cesium lead iodide perovskite solar cells with stabilized efficiency beyond 15%

As the black cesium lead iodide (CsPbI3) tends to transit into a yellow δ-phase at ambient, it is imperative to develop a stabilized black phase for photovoltaic applications. Herein, we report a distorted black CsPbI3 film by exploiting the synergistic effect of hydroiodic acid (HI) and phenylethylammonium iodide (PEAI) additives. It is found that the HI induces formation of hydrogen lead iodide (HPbI3+x), an intermediate to the distorted black phase with appropriate band gap of 1.69 eV; while PEAI provides nucleation for optimized crystallization. More importantly, it stabilizes the distorted black phase by hindering phase transition via its steric effects. Upon optimization, we have attained solar cell efficiency as high as 15.07%. Specifically, the bare cell without any encapsulation shows negligible efficiency loss after 300 h of light soaking. The device keeps 92% of its initial cell efficiency after being stored for 2 months under ambient conditions.Black phase cesium lead iodide perovskite is regarded as a promising candidate for solar cells, but it easily transits to undesired yellow phase. Herein, Wang et al. stabilized the black phase using molecular additives to achieve device efficiency beyond 15% with high light soaking stability.