Self-Assembly of 1‑Pyrenemethanol on ZnO Surface toward Combined Cathode Buffer Layers for Inverted Polymer Solar Cells

Solid alcohol 1-pyrenemethanol (PyM) was first introduced to modify the zinc oxide (ZnO) layer which is used in the inverted polymer solar cells (PSCs) as a cathode buffer layer (CBL). As a low-cost industrial product, the PyM can modify the surface defects and improve the electron mobility of ZnO CBL, which can be attributed to the self-assembly of PyM on the ZnO surface due to the hydrogen bonds and the conjugated structure in PyM. With a blend of PTB7:PC71BM as active layer, the device with ZnO/PyM CBL exhibited a notable power conversion efficiency (PCE) of 8.26%, which is better than that of control devices based on bare ZnO CBL (7.26%). With the addition of PyM, the device based on PTB7-Th:PC71BM showed a higher PCE of 9.10%, an obvious improvement from the 7.79% of control devices. There was no obvious change in device performance with the increase of PyM solution concentration, indicating that the device fabrications are thickness-insensitive. These results could be particularly useful in solution processing of buffer layer materials to high-efficiency organic solar cells.