A multiscale modeling study of loss processes in block-copolymer-based solar cell nanodevices

Abstract

Articles you may be interested inOptimizing the fabrication process and interplay of device components of polymer solar cells using a field-based multiscale solar-cell algorithm J. Chem. Phys. 142, 184902 (2015) Flexible photovoltaic devices possess promising perspectives in opto-electronic technologies, where high mobility and/or large-scale applicability are important. However, their usefulness in such applications is currently still limited due to the low level of optimization of their performance and durability. For the improvement of these properties, a better understanding and control of small-scale annihilation phenomena involved in the photovoltaic process, such as exciton loss and charge carrier loss, is necessary, which typically implicates multiple length-and time-scales. Here, we study the causes for their occurrence on the example of nanostructured diblock-and triblock-copolymer systems by making use of a novel solar-cell simulation algorithm and explore new routes to optimize their photovoltaic properties. A particular focus is set on the investigation of exciton and charge carrier loss phenomena and their dependence on the inter-monomeric interaction strength, chain architecture, and external mechanical loading. Our simulation results reveal that in the regime from low up to intermediate χ -parameters an increasing number of continuous percolation paths is created. In this parameter range, the internal quantum efficiency (IQE) increases up to a maximum, characterized by a minimum in the number of charge losses due to charge recombination. In the regime of high χ -parameters both block-copolymer systems form nanostructures with a large number of bottlenecks and dead ends. These lead to a large number of charge losses due to charge recombination, charge trapping, and a deteriorated exciton dissociation, resulting in a significant drop in the IQE. Moreover, we find that the photovoltaic performance of the triblock-copolymer material decreases with increasing mechanical loading, caused by a growing number of charge losses due to charge recombination and charge accumulation. Finally, we demonstrate that the process of charge trapping in defects can be reversed by changing the polarity of the electrodes, which confers these materials the ability to be used as charge storage media.

Quantum dynamical studies of ultrafast charge separation in nanostructured organic polymer materials: Effects of vibronic interactions and molecular packing

“…On a somewhat longer time scale (ie, a few picoseconds), quasi‐stationary polaronic, or exciton‐polaron states are reached, due to dephasing and relaxation on the molecular lattice structure. On even longer time scales of tens to hundreds of picoseconds and beyond, a transition to a kinetic regime occurs, which can be captured by multi‐scale approaches …”

Computation of full polymer-based photovoltaic nanodevices using a parametrized field-based multiscale solar-cell approach

“…Promising examples of novel 56 characteristics in polymer devices, which might be integrated 57 within nanocircuits, are e.g. memory effects [16], charge storage 58 capabilities of nanocapacitor arrays [17] and negative differential 59 resistance behavior [16,18]. However, the integration of these 60 new device functionalities within electronic nanocircuits fre- 61 quently poses considerable challenges for material scientists, 62 because a detailed understanding of their underlying mechanisms 63 is in most cases still lacking [16].…”

“…70 The causes for the low power conversion efficiency of PSCs have 71 primary been associated with loss phenomena of the elementary 72 particles, occurring during the photovoltaic process, such as pho- 73 ton loss, exciton loss and charge carrier loss [25]. Their complex 74 relationship and strong dependence on the structural-dynamical 75 characteristics of the photoactive material have been investigated 76 in various recent experimental [26][27][28][29] and theoretical studies 77 [17,[30][31][32][33][34]. For example, photon losses can be caused by the 78 [17,39].…”

“…Their complex 74 relationship and strong dependence on the structural-dynamical 75 characteristics of the photoactive material have been investigated 76 in various recent experimental [26][27][28][29] and theoretical studies 77 [17,[30][31][32][33][34]. For example, photon losses can be caused by the 78 [17,39]. One effective and widely used approximation procedure is, 228 for instance, the mean-field (MF) approximation, which is used …”

“…charge motion under the influence of the built-in 324 electric field, resulting from the difference between the electrode 325 work functions;(5) charge collection at the appropriate electrodes.326 To accomplish the dynamic evolution of the elementary particles,327 we used the FR method[17,[32][33][34]44,45], which implies that all 328 possible events are stored in a queue in order of ascending waiting 329 times and that the event with the smallest waiting time is exe-330 cuted at first. Moreover, we assumed that the particle motion331 within the system occurs through hopping between different sites 332 in space.…”