In recent years, joint efforts of a vast and expanding research community have led to a steady improvement of organic solar cell (OSC) power conversion efficiencies. However, even OSC record efficiencies of currently 8.3% [1] are still trailing behind the ones of their inorganic counterparts -a fact which can be attributed to the relatively low dielectric constants r ( 3 4) ε ªof the employed organic semiconductors. The resulting weak screening causes the primary photoexcitations, i.e. the singlet excitons S 1 created in the polymer, to be strongly bound, thus making thermally induced dissociation to free charge carriers highly improbable. In the bulk heterojunction (BHJ) solar cell concept, dissociation is driven by ultrafast photoinduced charge transfer between a donor and an acceptor material (e.g. a conjugated polymer -fullerene system). The interpenetrated donor -acceptor network leads to the creation of charge transfer complexes (CTC), i.e. bound electron-hole pairs at the heterointerface forming after singlet exciton dissociation. While the energetics of those complexes are already known to influence the overall OSC efficiency by setting the maximum limit for the open circuit voltage [2], the extent of the CTC's impact on the equally important photocurrent is still controversially debated [3,4]. Nevertheless, there exists a common notion that CTC can be precursors to at least some of the generated free charge carriers if the coulombic CTC binding energy can be overcome by an additional driving force. In order to contribute to the understanding of the underlying physical processes, we report on the determination of the binding energy 1 b,S E of the singlet exciton in poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and b,CTC E of the CTC of the PPV derivative blended with [6,6]-phenyl-C 61 butyric acid methylester (PCBM).Due to the finite binding energy, a certain amount of the created singlet excitons or CTC is not dissociated but recombines. The radiative part of the recombination can be observed as photoluminescence (PL). The application of an increasing external electric field constitutes an additional driving force which leads to an enhanced singlet exciton or CTC dissociation and thus to a reduction of the PL intensity. This field dependent PL quenching (PL(F)) has been observed for both singlet excitons and CTC for a variety of material systems [5,6] and is also regarded as a suitable technique for determining the binding energy [5,7] by relating it to the established Onsager -Braun model [8,9]. This model comprises Braun's adaption of the Onsager theory to the case of the electron-hole pair being the lowest excited state of the observed system [10] and thus ap-The influence of an external electric field on the photoluminescence intensity of singlet excitons and charge transfer complexes is investigated for a poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) diode and a bulk heterojunction of the PPV in combination with [6,6]-phenyl-C 61 butyric ac...
In this article, we elaborate on 10 current research questions related to the “teaching games for understanding” (TGfU) approach with the objective of both developing the model itself and fostering game understanding, tactical decision making, and game-playing ability in invasion and net/wall games: (1) How can existing scientific approaches from different disciplines be used to enhance game play for beginners and proficient players? (2) How can state-of-the-art technology be integrated to game-play evaluations of beginners and proficient players by employing corresponding assessments? (4) How can complexity thinking be utilized to shape day-to-day physical education (PE) and coaching practices? (5) How can game making/designing be helpfully utilized for emergent learning? (6) How could purposeful game design create constraints that enable tactical understanding and skill development through adaptive learning and distributed cognition? (7) How can teacher/coach development programs benefit from game-centered approaches? (8) How can TGfU-related approaches be implemented in teacher or coach education with the goal of facilitating preservice and in-service teachers/coaches’ learning to teach and thereby foster their professional development from novices to experienced practitioners? (9) Can the TGfU approach be considered a helpful model across different cultures? (10) Can physical/psychomotor, cognitive, affective/social, and cultural development be fostered via TGfU approaches? The answers to these questions are critical not only for the advancement of teaching and coaching in PE and sport-based clubs, but also for an in-depth discussion on new scientific avenues and technological tools.
The presented field experiment in an 11 vs. 11 soccer game set-up is the first to examine the impact of different formations (e.g. 4-2-3-1 vs. 3-5-2) on tactical key performance indicators (KPIs) using positional data in a controlled experiment. The data were gathered using player tracking systems (1 Hz) in a standardized 11 vs. 11 soccer game. The KPIs were measured using dynamical positioning variables like Effective Playing Space, Player Length per Width ratio, Team Separateness, Space Control Gain, and Pressure Passing Efficiency. Within the experimental positional data analysis paradigm, neither of the team formations showed differences in Effective Playing Space, Team Separateness, or Space Control Gain. However, as a theory-based approach predicted, a 3-5-2 formation for the Player Length per Width ratio and Pressure Passing Efficiency exceeded the 4-2-3-1 formation. Practice task designs which manipulate team formations therefore significantly influence the emergent behavioral dynamics and need to be considered when planning and monitoring performance. Accordingly, an experimental positional data analysis paradigm is a useful approach to enable the development and validation of theory-oriented models in the area of performance analysis in sports games.
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