wangzhaowei

Although tin oxide (SnO₂) has been employed recently as an efficient electron-transporter to realize highly efficient organometal halide perovskite solar cells (PVSCs), it is still quite challenging to apply it through facile solution-based synthesis at low enough temperature (<150 °C) to be compatible with the roll-to-roll printing on polymer substrates. In this work, a dual-fuel combustion method has been successfully adapted to modulate the exothermic characteristics and processing temperature (140 °C) of SnO₂ to achieve homogeneous and crystalline thin film as efficient electron-transporting layer for PVSCs. The fabricated SnO₂ film not only has high transparency (from 350 nm to near-infrared region) but also possesses good electron extraction ability, as evidenced by the efficient PL quenching in bilayered SnO₂/CH₃NH₃PbI₃ film. By passivating SnO₂ surface with a C₆₀-containing self-assembled monolayer (C₆₀-SAM), a high power conversion efficiency (PCE_max) of >15% with negligible hysteresis can be achieved in PVSC. This demonstrates the great potential of applying this dual-fuel combustion process to improve processability and charge-transporting properties of metal oxides for organic electronics applications.

A low-temperature (<150 °C), solution processible SnO₂ electron-transporting layer is prepared via a dual-fuel combustion method. The fabricated SnO₂ shows a decent charge-collecting capability from perovskite absorber to realize a maximium power conversion efficiency (PCE_max) of ≈13% of the derived device. By further passivating the SnO₂ surface with C₆₀-containing self-assembled monolayer, an improved PCE_max of >15% with negligible hysteresis is demonstrated.

In article number 1500616, Y. Sevinchan and co-workers investigate the photo-induced charge separation process at a metal oxide/polymer interface. Incorporation of a Cs dopant in the metal oxide reduces the density of gap states at the oxide surface, thus lowering the number of bound charge pairs formed at the organic/inorganic interface. This reduction in interfacial trapping suppresses the recombination and enhances the photocurrent in hybrid photovoltaic cells.

In article number 1502206, Aleksandra B. Djurišić and co-workers discuss whether excess PbI₂ is beneficial for perovskite solar cell performance. The presence of unreacted PbI₂ is commonly believed to be beneficial to the efficiency of perovskite solar cells. However, it results in an intrinsic instability of the illuminated film even in inert atmosphere, leading to accelerated film degradation under illumination.

In article number 1502027, Dehong Chen, Yi-Bing Cheng, Rachel A. Caruso and co-workers demonstrate the structural tuning of titania, producing films of nanoparticles, nanowires or nanosheets for perovskite solar cells. The porous network and fast electron transfer of the nanowire and nanosheet thin films enable perovskite infiltration, facilitate charge extraction and suppress charge recombination.

In organic donor–acceptor systems, ultrafast interfacial charge transfer (CT), charge separation (CS), and charge recombination (CR) are key determinants of the overall performance of photovoltaic devices. However, a profound understanding of these photophysical processes at device interfaces remains superficial, creating a major bottleneck that circumvents advancements and the optimization of these solar cells. Here, results from time-resolved laser spectroscopy and high-resolution electron microscopy are examined to provide the fundamental information necessary to fabricate and optimize organic solar cell devices. In real time, CT and CS are monitored at the interface between three fullerene acceptors (FAs) (PC₇₁BM, PC₆₁BM, and IC₆₀BA) and the PTB7-Th donor polymer. Femtosecond transient absorption (fs-TA) data demonstrates that photoinduced electron transfer from the PTB7-Th polymer to each FA occurs on the sub-picosecond time scale, leading to the formation of long-lived radical ions. It is also found that the power conversion efficiency improves from 2% in IC₆₀BA-based solar cells to >9% in PC₇₁BM-based devices, in support of our time-resolved results. The insights reported in this manuscript provide a clear understanding of the key variables involved at the device interface, paving the way for the exploitation of efficient CS and subsequently improving the photoconversion efficiency.

A complete understanding of the charge transfer, charge separation, and charge recombination at D/A interfaces is integral for boosting solar cell photoconversion efficiency (PCE). Time-resolved laser spectroscopy and high-resolution electron microscopy provide a basis for accomplishing the high performance solar cell. The device optimization enhanced the PCE from 2% in IC₆₀BA-based to >9% in PC₇₁BM-based solar cells.

Vapor-based deposition technique is considered as a promising approach for preparing a high-quality and uniform perovskite thin film. With evolution from coevaporation deposition to a low-pressure vapor-assisted solution process, both energy budget and reaction yield for perovskite film fabrications are improved. In this paper, a low-pressure hybrid chemical vapor deposition (LPHCVD) method is applied to fabricate CH₃NH₃PbI₃ perovskite films. The crucial dependence of working pressure on the perovskite formation is revealed. Moreover, the reaction time plays an important role in controlling the quality of the synthesized perovskite film. Efficient perovskite solar cells of 14.99% (mesoscopic), 15.37% (planar), and perovskite modules (active area of 8.4 cm²) of 6.22% are achieved by this LPHCVD method.

Highly efficient perovskite solar cells are made by low-pressure hybrid chemical vapor growth with superior uniformity. Small-area planar and mesoscopic devices obtain 15% power conversion efficiency with submodule of 6.22%.

The light intensity dependence of the main photoelectrical parameters of the nonfullerene small-molecule bulk heterojunction (BHJ) solar cells p-DTS(FBTTh₂)₂:perylene diimide (T1:PDI) shows that the nongeminate recombination losses play an important role in this system. A simple approach for the quantitative analysis of capacitance spectroscopy data of the organic BHJ solar cells, which allows to determine the density of free charge carriers as a function of applied bias under standard working conditions, is demonstrated. Using the proposed capacitance spectroscopic technique, the nongeminate recombination losses in the T1:PDI solar cells are quantitatively characterized in the scope of the bimolecular- and trap-assisted recombination mechanisms. Their contributions are separately analyzed within a wide range of the applied bias.

A simple method for the determination of the density of free charge carriers and quantification of nongeminate recombination losses in organic-bulk heterojunction solar cells, based on the analysis of capacitance spectroscopy data, is presented. The proposed method is applied to the analysis of nongeminate recombination losses in nonfullerene T1: perylene diimide small-molecule solar cells in the scope of bimolecular- and trap-assisted recombination mechanisms under 1 sun illumination.

The role of the common stress factors such as high temperature, humidity, and UV irradiation on interface adhesion of roll-to-roll fabricated organic photovoltaic (OPV) devices is investigated. The samples range from bare front electrodes to complete devices. It is shown that applying single stress or combinations of stresses onto the samples variably affect the adhesion properties of the different interfaces in the OPV device. It is revealed that while the exposure of the complete devices to the stresses results in the loss of photovoltaic performance, some interfaces in the devices present improved adhesion properties. Depth profiling analysis on the fractured samples reveals interdiffusion of layers in the structure, which results in the increase of adhesion and change of the debond path. It is shown that through diffusion and intermixing of internal interfaces coupled stresses can increase the adhesion of OPV interfaces by over tenfold. The results are additionally compared to the photovoltaic performance of the complete devices.

The effect of high temperature, humidity, and UV irradiation on the interface adhesion of roll-to-roll fabricated organic photovoltaic (OPV) devices is investigated. The samples range from bare front electrodes to complete devices. It is shown that applying single stress or combinations of stresses onto the samples variably affects the adhesion properties of the different interfaces in the OPV device.