conducting domains. [ 19 ] This concomitant increase of structural order and phase separation complicates efforts to decouple the effects of order and domain connectivity on charge transport. For that reason as well as the diffi culty of even qualitative measures of domain connectivity, it is generally unknown how much the connectivity of conductive domains, or lack thereof, limits the charge carrier mobility in SSM BHJ solar cells.In this communication, we report on the factors limiting charge carrier mobility in blend fi lms consisting of a range of molecular donor material systems ( Figure 1 A) using phenyl-C71-butyric acid methyl ester (PC 71 BM) as the electron acceptor. The donor materials considered in this study are]thiadiazole]) (T1) each of which has been reported on previously with peak power conversion effi ciencies ranging from 3% to 7%. [20][21][22] Previous studies hinted that the charge transport properties of these material systems respond differently to the ratio of donor to acceptor in the blend fi lm with a much greater dependence on donor content observed in SM2:PC 71 BM and H1:PC 71 BM than in T1:PC 71 BM fi lms. [ 5,22 ] Here, we delineate the effects of order and domain connectivity on charge carrier mobility by incrementally varying the weight ratio of donor to acceptor. The varying trends in hole and electron mobilities for each system indicate the presence of multiple processes governing charge transport. Using a combination of grazing incidence wide-angle X-ray scattering (GIWAXS) and temperature dependent mobility measurements, it is found that structural order in the π-π stacking direction is a key determinant of the activation energy for hole transport. Furthermore, this combinatorial approach reveals that the electrical connectivity between domains can vary widely between material systems and in many cases is the primary limitation to charge carrier mobility in blend fi lms. These fi ndings offer unique insight into the factors limiting charge carrier mobility in SSM blend fi lms and thus solar cell performance.To start, hole and electron mobilities were determined from the current-voltage response of single-carrier diodes made using blend fi lms with 0% to 100% donor content. As SSM BHJ fi lms are highly sensitive to processing conditions, only the weight ratio of donor to acceptor was varied while the choice of solvent(s) and thermal processing was held constant Solution processed small molecule-based bulk heterojunction (SSM BHJ) solar cells have emerged as a promising technology with recent reports of power conversion effi ciencies (PCEs) exceeding 9% for a variety of molecular architectures. [1][2][3][4] The steady rise in performance of SSM BHJ solar cells has been well documented and is known to largely be a result of improved charge carrier mobility. [ 5 ] Indeed, charge carrier mobility has been identifi ed as one of the most critical parameters for continued improvement of both small molecule and polymer based solar cells. [6][7][8][9][10] Despite this progress, the under...
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