Modulating secondary growth of perovskite grains through residual solvent evaporation.

Over the past decade, perovskite solar cells (PSCs) have attracted enormous attention due to their high performance. One key to fabricating high-quality perovskite films lies in controlling the volatilization rate of residual solvents during the annealing process. This study systematically investigates how different protective substrates affect the volatilization rate of residual solvent in perovskite films. By adjusting the direction and rate of evaporation, the supersaturation time of the solution was precisely controlled, leading to effective recrystallization of the grains. Concurrently, the annealing time was optimized to enhance film quality further. This optimization aimed to increase crystallinity, reduce defects, and thereby minimize non-radiative recombination centers. Implementing these methodologies, particularly the use of filter paper as a protective substrate during a 2-minute annealing process, significantly improved the fill factor (FF) and open-circuit voltage (VOC) of the PSCs. This led to a remarkable 5.26% improvement in power conversion efficiency (PCE) compared to control devices. The strategies employed in this work demonstrate significant potential in improving PSC film quality. This approach not only advances our understanding of film formation dynamics but also provides a practical guideline for future PSC fabrication.

Quasi-Heteroface Perovskite Solar Cells.

Perovskite solar cells (PSCs) have attracted unprecedented attention due to their rapidly rising photoelectric conversion efficiency (PCE). In order to further improve the PCE of PSCs, new possible optimization path needs to be found. Here, quasi-heteroface PSCs (QHF-PSCs) is designed by a double-layer perovskite film. Such brand new PSCs have good carrier separation capabilities, effectively suppress the nonradiative recombination of the PSCs, and thus greatly improve the open-circuit voltage and PCE. The root cause of the performance improvement is the benefit from the additional built-in electric field, which is confirmed by measuring the external quantum efficiency under applied electric field and Kelvin probe force microscope. Meanwhile, an intermediate band gap perovskite layer can be obtained simply by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. Tunability of the band gap is obtained by varying the film thicknesses of the narrow and wide band gap layers. This phenomenon is quite different from traditional inorganic solar cells, whose band gap is determined only by the narrowest band gap layer. It is believed that these QHF-PSCs will be an effective strategy to further enhance PCE in PSCs and provide basis to further understand and develop the perovskite materials platform.

Gradient Energy Alignment Engineering for Planar Perovskite Solar Cells with Efficiency Over 23.

An electron-transport layer (ETL) with appropriate energy alignment and enhanced charge transfer is critical for perovskite solar cells (PSCs). However, interfacial energy level mismatch limits the electrical performance of PSCs, particularly the open-circuit voltage (VOC ). Herein, a simple low-temperature-processed In2 O3 /SnO2 bilayer ETL is developed and used for fabricating a new PSC device. The presence of In2 O3 results in uniform, compact, and low-trap-density perovskite films. Moreover, the conduction band of In2 O3 is shallower than that of Sn-doped In2 O3 (ITO), enhancing the charge transfer from perovskite to ETL, thus minimizing VOC loss at the perovskite and ETL interface. A planar PSC with a power conversion efficiency of 23.24% (certified efficiency of 22.54%) is obtained. A high VOC of 1.17 V is achieved with the potential loss at only 0.36 V. In contrast, devices based on single SnO2 layers achieve 21.42% efficiency with a VOC of 1.13 V. In addition, the new device maintains 97.5% initial efficiency after 80 d in N2 without encapsulation and retains 91% of its initial efficiency after 180 h under 1 sun continuous illumination. The results demonstrate and pave the way for the development of efficient photovoltaic devices.

Efficient and Stable Perovskite Solar Cell Achieved with Bifunctional Interfacial Layers.

The elaborate control of the surface morphologies and trap states of solution-processed perovskite films significantly governs the photovoltaic performance and moisture resistance of perovskite solar cells (PSCs). Herein, a thin layer of poly(triaryl amine) (PTAA) was unprecedentedly devised on top of perovskite quasi-film by spin-coating PTAA/chlorobenzene solution before annealing the perovskite film. This treatment induced a smooth and compact perovskite layer with passivated surface defects and grain boundaries, which result in a significantly reduced charge recombination. Besides, the time-resolved photoluminescence spectra of the PTAA-treated perovskite films confirmed a faster charge transfer and a much longer lifetime compared to the control cells without the PTAA treatment. Moreover, such a hydrophobic polymer atop the perovskite layer could effectively protect the perovskite against humidity and retain 83% of its initial efficiency in contrast to 56% of control cells stored for 1 month in ambient conditions (25 °C, 35 RH%). As a result, the PTAA-treated PSCs displayed an average efficiency of 17.77% (with a peak efficiency of 18.75%), in contrast to 16.15% of the control cells, and enhanced stability. These results demonstrate that PTAA and the method thereof constitute a promising passivation strategy for constructing stable and efficient PSCs.

Highly efficient organic tandem solar cell with a SubPc interlayer based on TAPC:C70 bulk heterojunction.

We report a small molecule tandem organic photovoltaic (OPV) cell with a high power conversion efficiency (PCE) of 7.27%. This cell contains two subcells with an identical mixed active layer of C70:5 wt%TAPC (1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane). The performance was dramatically improved by simply inserting a thin boron subphthalocyanine chloride (SubPc) interlayer, which results in an increase of the short-circuit current and open-circuit voltage as well as a decrease of the series resistance of the tandem cell. The response of the cell only contributed from the absorption of C70. The high PCE was attributed to the high absorption efficiency of C70 and improved holes extraction efficiency at the anode due to the band bending occurs at both MoO3/SubPc and SubPc/C70:5 wt%TAPC interfaces.

Efficient and stable planar heterojunction perovskite solar cells with an MoO3/PEDOT:PSS hole transporting layer.

A solution processed MoO3/PEDOT:PSS bilayer structure is used as the hole transporting layer to improve the efficiency and stability of planar heterojunction perovskite solar cells. Increased hole extraction efficiency and restrained erosion of ITO by PEDOT: PSS are demonstrated in the optimized device due to the incorporation of an MoO3 layer.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant.

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

High-performance organic small-molecule panchromatic photodetectors.

High-performance panchromatic organic photodetectors (OPDs) containing small molecules lead phthalocyanine (PbPc) and C70 fullerene as donor and acceptor, respectively, were demonstrated. The OPDs had either a PbPc/C70 planar heterojunction (PHJ) or a PbPc/PbPc:C70/C70 hybrid planar-mixed molecular heterojunction (PM-HJ) structure. Both the PHJ and the PM-HJ devices showed a broad-band response that covered wavelengths from 300 to 1100 nm. An external quantum efficiency (EQE) higher than 10% and detectivity on the order of 10(12) Jones were obtained in the wavelength region from 400 to 900 nm for the PHJ device. The EQE in the near-infrared region was enhanced by using the PM-HJ device structure, and a maximum EQE of 30.2% at 890 nm was observed for the optimized device with a 5% PbPc-doped C70 layer. Such an EQE is the highest at this wavelength of reported OPDs. The detectivity of the PM-HJ devices was also higher than that of the PHJ one, which is attributed to the increased efficiency of exciton dissociation in bulk heterojunction structure, increased absorption efficiency caused by formation of triclinic PbPc in the PbPc:C70 mixed film when it was deposited on a pristine PbPc layer, and high hole mobility of the PbPc-doped C70 layer.