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The organic photodiode (OPD) is a promising building block for solution‐processable, flexible, lightweight, and miniaturized photodetectors, ideal for wearable applications. Despite the advances in materials used in OPDs, their photocurrent and light responsivity are limited, and alternative methods are required to boost the signal response. Herein, a miniaturized organic electrochemical transistor (OECT) is integrated with an OPD module to unlock the potential of OPDs to acquire physiological signals. In this integrated photodetector (IPD) system, the light intensity regulates the OPD voltage output that modulates the OECT channel current. The high transconductance of the OECT provides efficient voltage‐to‐current conversion, enhancing the signal‐to‐noise ratio on the sensing site. A microscale, p‐type enhancement‐mode OECT with high gm and fast switching speed performs better in this application than depletion‐mode OECT of the same geometry. The IPD achieves a photocurrent and responsivity 318 and 140 times higher than the standalone OPD, respectively. It is shown that with the IPD, the amplitude of the photoplethysmogram signals detected by the OPD is enhanced by a factor of 2.9 × 103, highlighting its potential as a wearable biosensor and to detect weak, often uncaptured, light‐based signals from living systems. [ABSTRACT FROM AUTHOR]

New polymer donors and nonfullerene acceptors have elevated the performance and stability of solar cells to higher grounds. To achieve their full potential, they require their adaptation to scalable and cost‐effective solution manufacturing techniques for large area deposition. Likewise, formulating scalable solution‐based transport layer inks that are compatible with the photoactive layer is imperative. This manuscript reports the full integration of solution‐based transport layers and electrode alongside a PTB7‐Th:IEICO‐4F bulk heterojunction in inverted architecture through inkjet‐printing, resulting in power conversion efficiencies up to 12.4% opaque devices and 9.5% semitransparent devices with average visible transmittance values of 50.1%, including hole transport layer. The wetting envelope of the highly‐hydrophobic photoactive layer alongside the surface energy of candidate solutions and solvents allows the formulation of thick transport layer inks that are compatible with the drop‐on‐demand inkjet‐printing process and yield uniform and homogenous films. Moreover, the surface energy components of the donor and acceptor serves as a fingerprint to assess the vertical stratification of the photoactive layer with the inclusion of different solvents. This methodology addresses a scale‐up bottleneck of solution‐based transport layers for high‐efficiency organic cells, enabling its adaptation to high‐throughput techniques including slot‐die and roll‐to‐roll coating. [ABSTRACT FROM AUTHOR]

Abstract: Nonfullerene acceptors (NFAs) in blends with highly crystalline donor polymers have been shown to yield particularly high device voltage outputs, but typically more modest quantum yields for photocurrent generation as well as often lower fill factors (FF). In this study, we employ transient optical and optoelectronic analysis to elucidate the factors determining device photocurrent and FF in blends of the highly crystalline donor polymer PffBT4T‐2OD with the promising NFA FBR or the more widely studied fullerene acceptor PC71BM. Geminate recombination losses, as measured by ultrafast transient absorption spectroscopy, are observed to be significantly higher for PffBT4T‐2OD:FBR blends. This is assigned to the smaller LUMO‐LUMO offset of the PffBT4T‐2OD:FBR blends relative to PffBT4T‐2OD:PC71BM, resulting in the lower photocurrent generation efficiency obtained with FBR. Employing time delayed charge extraction measurements, these geminate recombination losses are observed to be field dependent, resulting in the lower FF observed with PffBT4T‐2OD:FBR devices. These data therefore provide a detailed understanding of the impact of acceptor design, and particularly acceptor energetics, on organic solar cell performance. Our study concludes with a discussion of the implications of these results for the design of NFAs in organic solar cells. [ABSTRACT FROM AUTHOR]