Understanding the photophysics of charge generation in organic semiconductors is a critical step toward the further optimization of organic solar cells. The separation of electron–hole pairs in systems with large energy offsets is relatively well-understood; however, the photophysics in blends with low driving energy remains unclear. Herein, we use the material system PffBT4T-2OD:PC71BM as an example to show that the built-in electric field plays a critical role toward long-range charge separation in high-performance devices. By using steady-state and time-resolved spectroscopic techniques, we show that in neat films an energetic barrier impedes polymer exciton dissociation, preventing charge transfer to the fullerene acceptor. In complete devices, this barrier is diminished due to the built-in electric field provided by the interlayers/contacts and accompanying space-charge distribution. The observed behavior could also be relevant to other systems with low driving energy and emphasizes the importance of using complete devices, rather than solely films, for photophysical studies.

Controlling the morphology of metal halide perovskite layers during processing is critical for the manufacturing of optoelectronics. Here, a strategy to control the microstructure of solution‐processed layered Ruddlesden–Popper‐phase perovskite films based on phenethylammonium lead bromide ((PEA)2PbBr4) is reported. The method relies on the addition of the organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b]benzothiophene (C8‐BTBT) into the perovskite formulation, where it facilitates the formation of large, near‐single‐crystalline‐quality platelet‐like (PEA)2PbBr4 domains overlaid by a ≈5‐nm‐thin C8‐BTBT layer. Transistors with (PEA)2PbBr4/C8‐BTBT channels exhibit an unexpectedly large hysteresis window between forward and return bias sweeps. Material and device analysis combined with theoretical calculations suggest that the C8‐BTBT‐rich phase acts as the hole‐transporting channel, while the quantum wells in (PEA)2PbBr4 act as the charge storage element where carriers from the channel are injected, stored, or extracted via tunneling. When tested as a non‐volatile memory, the devices exhibit a record memory window (>180 V), a high erase/write channel current ratio (104), good data retention, and high endurance (>104 cycles). The results here highlight a new memory device concept for application in large‐area electronics, while the growth technique can potentially be exploited for the development of other optoelectronic devices including solar cells, photodetectors, and light‐emitting diodes.

Despite tremendous advances in improving the efficiency of organic solar cells above 14%, the environmental stability of such devices remains an essential and widely inadequately addressed challenge. Understanding the underlying principles of device degradation is a critical step toward further development and commercialization of organic photovoltaics. Herein, we report on the effect of oxygen exposure on the operation and degradation of highly efficient PffBT4T-2OD:PC 71 BM photovoltaic devices. Ultrafast pump−probe transient absorption (TA) measurements and ultrasensitive photothermal deflection spectroscopy (PDS) in combination with field-effect transistors suggest that oxygen-induced doping of the active layer is responsible for the severe degradation of the photovoltaic performance. We find that light exposure further accelerates this effect without causing photo-oxidation of the materials.

Engineering the energetics of perovskite photovoltaic devices through the deliberate introduction of dipoles to control the built-in potential of the devices offers the opportunity to enhance their performance without the need to modify the active layer itself. In this work, we demonstrate how the incorporation of molecular dipoles into the bathocuproine (BCP) hole-blocking layer of inverted perovskite solar cells improves the device open-circuit voltage (VOC) and consequently, its performance. We explore a series of four thiaazulenic derivatives that exhibit increasing dipole moments and demonstrate that these molecules can be introduced into the solution-processed BCP layer to effectively increase the built-in potential within the device, without altering any of the other device layers. As a result the VOC of the devices is enhanced by up to 130 mV with larger dipoles resulting in higher VOCs. To investigate the limitations of this approach, we employ numerical device simulations that demonstrate that the highest dipole derivatives used in this work eliminate all limitations on the VOC stemming from the built-in potential of the device.

The mixed ionic–electronic nature of lead halide perovskites makes their performance in solar cells complex in nature. Ion migration is often associated with negative impacts—such as hysteresis or device degradation—leading to significant efforts to suppress ionic movement in perovskite solar cells. In this work, we demonstrate that ion trapping at the perovskite/electron transport layer interface induces band bending, thus increasing the built-in potential and open-circuit voltage of the device. Quantum chemical calculations reveal that iodine interstitials are stabilized at that interface, effectively trapping them at a remarkably high density of ∼10 21 cm –3 which causes the band bending. Despite the presence of this high density of ionic defects, the electronic structure calculations show no sub-band-gap states (electronic traps) are formed due to a pronounced perovskite lattice reorganization. Our work demonstrates that ionic traps can have a positive impact on device performance of perovskite solar cells.

AgBiS2 nanocrystal solar cells are among the most sustainable emerging photovoltaic technologies. Their environmentally-friendly composition and low energy consumption during fabrication make them particularly attractive for future applications. However, much...

Organic phototransistors can enable many important applications such as nonvolatile memory, artificial synapses, and photodetectors in next‐generation optical communication and wearable electronics. However, it is still a challenge to achieve a big memory window (threshold voltage response ∆Vth) for phototransistors. Here, a nanographene‐based heterojunction phototransistor memory with large ∆Vth responses is reported. Exposure to low intensity light (25.7 µW cm−2) for 1 s yields a memory window of 35 V, and the threshold voltage shift is found to be larger than 140 V under continuous light illumination. The device exhibits both good photosensitivity (3.6 × 105) and memory properties including long retention time (>1.5 × 105 s), large hysteresis (45.35 V), and high endurance for voltage‐erasing and light‐programming. These findings demonstrate the high application potential of nanographenes in the field of optoelectronics. In addition, the working principle of these hybrid nanographene‐organic structured heterojunction phototransistor memory devices is described which provides new insight into the design of high‐performance organic phototransistor devices.

Engineering the energetics of perovskite solar cells through the introduction of surface dipoles that assist with charge carrier extraction is a promising route to enhance the device performance without altering other device layers or fabrication parameters. In this work, we introduce four different derivatives of dicationic phosphonium-bridged ladder stilbenes (PYMC) in inverted perovskite solar cells with the device structure of ITO/Meo-2pacz/perovskite/PYMC/phenyl-C61-butyric acid methyl ester (PCBM)/bathocuproine/Ag. We show that the derivatives introduce a dipole at the perovskite/PCBM interface, which for derivatives with suitable energy levels can enhance the charge carrier extraction, leading to a quenched photoluminescence of perovskite thin films and an improved photovoltaic performance. As a result, both a higher average and maximum power conversion efficiency could be achieved and an overall better device reproducibility. This work highlights the significant potential of energetics engineering between perovskites and transport layers in perovskite solar cells for highly efficient photovoltaic devices.