Management of the light distribution within the photoactive layer for high performance conventional and inverted polymer solar cells

Improving the light absorption of the photoactive layer is a key issue to enhance the photovoltaic performance of polymer solar cells (PSCs). Herein, the transfer-matrix method is used to model the absorption spectra and optical electric field distribution within the multilayer stack of conventional and inverted PSCs based on PBDTTT-C-T:PC₇₀BM blends. The simulation results show that the short-circuit current density (J_sc) of the devices increases with increasing photoactive layer thickness and an oscillation can be observed for both conventional and inverted devices. By applying an inverted architecture, higher optical electric field energy dissipation in the photoactive layer can be realized, and higher J_sc can be achieved. Guided by the simulation results, high performance conventional and inverted PSCs based on PBDTTT-C-T:PC₇₀BM are experimentally fabricated. Comparing the external quantum efficiency (EQE) with the absorption spectra for both devices, the increased J_sc for the inverted device is attributed mainly to the enhanced absorption. The conventional device shows a power conversion efficiency (PCE) of 7.09%, while the inverted device shows enhanced J_sc and FF, and the PCE reaches 8.81%, which is increased by 24.3% in comparison with that of the conventional device. The agreement between the modeling and experimental results confirms the directive function of optical modeling on device design and optimization.