Fine Tuning the Light Distribution within the Photoactive Layer by Both Solution-Processed Anode and Cathode Interlayers for High Performance Polymer Solar Cells

Light management is important for improving light absorption within active layers in polymer solar cells (PSCs). Electrode buffer layers play an important role in modulating the distribution of optical electric filed within the photoactive layer. Herein, the authors employ solution-processed WO_x or ReO_x to substitute the acidic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the anode buffer layer and ZrAcac or HfAcac to replace Mg as the cathode buffer layer. Optical transfer matrix formalism simulation is used to model the absorption spectra, exciton generation rate, and optical electric field distribution of devices. Simulated results shows that stronger absorption, quicker exciton generation rate, and more reasonable photoelectric field distribution can be achieved in the photoactive layer with solution-processed buffer layer modification, which results in a higher short-circuit current density (J_sc). Under the guidance of theoretical simulation, the device with architecture of ITO/WO_x/PTB7-Th:PC₇₁BM/HfAcac/Al is optimized. Compared with the traditional PEDOT:PSS-Mg based device, the J_sc is increased from 16.60 to 18.61 mA cm⁻² and the best power conversion efficiency (PCE) is increased from 9.02% to 10.60% for the device with WO_x-HfAcac modification, which is among the best values reported for fullerene-based PSCs. The good agreement between simulated and experimental results indicates that optical model is a useful tool for device design and optimization.