Drift-Diffusion Modeling of the Effects of Structural Disorder and Carrier Mobility on the Performance of Organic Photovoltaic Devices

Abstract

We probe the effects of structural disorder on the performance of organic photovoltaic (OPV) devices via Drift-Diffusion (D-D) modeling. We utilize ensembles of spatially disordered 1-dimensional mobility profiles to approximate the 3-dimensional structural disorder present in actual devices. Each replica in our ensemble approximates one high-conductivity pathway through the threedimensional network(s) present in a polymer-based bulk heterojunction solar cell, so that the ensemble-averaged behavior provides a good approximation to a full 3-dimensional structurally disordered device. Our calculations show that the short circuit current, fill factor and power conversion efficiency of simulated devices are all negatively impacted by the inclusion of structural disorder, but that the open circuit voltage is nearly impervious to structural defects. This is in contrast to energetic disorder, where previous studies found that spatial variation in the energy in OPV active layers causes a decrease in the open circuit voltage. We also show that structural disorder causes the greatest detriment to device performance for feature sizes between 2 nm and 10 nm. Since this is on the same length scale as the fullerene crystallites in experimental devices, it suggests both that controlling structural disorder is critical to the performance of OPV devices and that the effects of structural disorder should be included in future D-D modeling studies of organic solar cells.

Understanding How Polymer Properties Control OPV Device Performance: Regioregularity, Swelling, and Morphology Optimization Using Random Poly(3-butylthiophene-co-3-octylthiophene) Polymers

“…We also show in the SI the correlation of relative fraction crystallinity with other device performance figures of merit, including the short-circuit current, open-circuit voltage, and fill factor. We find that the relative fraction of crystallinity does not affect the open-circuit voltage of the devices, a result consistent with drift–diffusion simulations that have shown that V OC is relatively impervious to disorder and local environment . Instead, the correlation between relative crystalline fraction and device efficiency comes about because of correlation with both the short-circuit current and fill factor.…”

“…67 We also show in the SI the correlation of relative fraction crystallinity with other device performance figures of merit, including the short-circuit current, open-circuit voltage, and fill factor. We find that the 68 Instead, the correlation between relative crystalline fraction and device efficiency comes about because of correlation with both the short-circuit current and fill factor. C. Swelling Studies of Pure RBO x Films.…”

Leakage Current Induced by Energetic Disorder in Organic Bulk Heterojunction Solar Cells: Comprehending the Ultrahigh Loss of Open-Circuit Voltage at Low Temperatures

“…(2,3,4,6) numerically many types of macroscopic quantities for a working device can be calculated. The details for device model implementation are elaborated in numerous literatures and thus are omitted here [32][33][34] . In our simulation, initially the Onsager-Braun theory is incorporate into the model to account for the temperature variation of the CT state dissociation (or charge generation) rate, which can be written as 33,35…”

Drift-Diffusion Studies of Compositional Morphology in Bulk Heterojunctions: The Role of the Mixed Phase in Photovoltaic Performance

“…The relative non-dependence of an OPV device's V OC on active layer morphological features, such as the presence of a mixed-phase, is in line with our previous work that showed little effect of structural disorder on the device open circuit voltage. [34] IV. CONCLUSIONS With this study we have illustrated that the mixedcomposition phase can have both beneficial and detrimental effects on the overall performance of polymer/fullerene BHJ photovoltaic devices.…”

“…[30,31] Other groups have focused on the impact of structural disorder and morphological features by performing 2-D drift-diffusion simulations to study the effects of phase separation and component arrangement on device performance [26,28,29,32,33]; we also have presented a 1-D method for examining structural disorder based on D-D simulations of ensembles of 1-D devices with position-dependent mobility profiles. [34] In this study, we present a set of 2-D drift-diffusion simulations specifically designed to probe the effects of the presence of a controllably varied mixed-composition, interfacial phase on device performance. We begin by utilizing morphologies generated by Cahn-Hilliard (C-H) modeling of binary fluid phase separation, as has been employed successfully in previous 2-D D-D modeling studies of OPVs.…”