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Abstract: Recently, the influence of molecular weight (Mn) on the performance of polymer solar cells (PSCs) is widely investigated. However, the dependence of optimal thickness of active layer for PSCs on Mn is not reported yet, which is vital to the solution printing technology. In this work, the effect of Mn on the efficiency and especially optimal thickness of the active layer for PBTIBDTT‐S‐based PSCs is systematically studied. The device efficiency improves significantly as the Mn increases from 12 to 38 kDa, and a remarkable efficiency of 10.1% is achieved, which is among the top efficiencies of wide‐bandgap polymer:fullerene PSCs. Furthermore, the optimal thickness of the active layer is also greatly increased from 62 to 210 nm with increased Mn. Therefore, a device employing a thick (>200 nm) active layer with power conversion efficiency exceeding 10% is achieved by manipulating Mn. This exciting result is attributed to both the improved crystallinity, thus hole mobility, and preferable polymer orientation, thus morphology of active layer. These findings, for the first time, highlight the significant impact of Mn on the optimal thickness of active layer for PSCs and provide a facile way to further improve the performance of PSCs employing a thick active layer. [ABSTRACT FROM AUTHOR]

A spray-coating method, named as partially overlapped spray-coating (POSC) with winding path, was developed to deposit homogenous film over large area and employed to fabricate polymer solar cell (PSC) modules. The photoactive layer consisting of the conjugated polymer PBTI3T and the fullerene derivative PCBM[70] was obtained by optimizing the ink formulations and spray-coating parameters, which determines the morphology and film thickness. The lab-scale PSC (0.09 cm 2 ) fabricated by the POSC technique achieved a power conversion efficiency (PCE) of 6.63%, which is comparable to the spin-coated one. The POSC technique was then applied to up-scaling fabrication of PSC modules. A PCE as high as 5.27% was achieved for the module with 38.5 cm 2 photoactive area, which is so far the highest one with comparable size, to the best of our knowledge. It shows the POSC technique developed in this work is very successful for fabricating high-performance PSC modules, which paves a new way for film deposition in continuous roll-to-roll production. [ABSTRACT FROM AUTHOR]

Although the power conversion efficiency (PCE) of small-area polymer solar cells (PSCs) has now surpassed 10% upon various optimizations, it is still a challenge to improve the performance of large-area device partially due to the problems encountered in film morphology optimization and incompatibility of using these optimizations for size scale-up. Herein, we reported a method to effectively improve the morphology of photoactive layer and thus device efficiency under ambient atmosphere by using spray coating technique. It was found that by finely adjusting the parameters of the instrument, and the properties of the “electronic ink”, the dynamics of solvent evaporation after film deposition could be controlled. By resorting to a few techniques for morphology characterization, it confirmed that the resulting blend film showed desirable vertical phase separation where polymer enriched near the anode and PCBM adjacent to the cathode. The graded composition is beneficial for the efficient charge transportation as well as eventual charge collection. By using PBDT-TFQ/PC 71 BM composite as an example, the exceptional high PCEs of 4.6% and 4.1% were achieved for the devices with the size of 1.0 and 10.2 cm 2 , respectively. In comparison to conventional device fabrication process, this method is not only simple without additional treatment steps, but also dramatically increases the device efficiency, which opens a new way for fabricating highly efficient large-area PSCs. [ABSTRACT FROM AUTHOR]