Improvement in the efficiency of organic solar cells using a low-temperature evaporable optical spacer

We demonstrate the enhancement in performance of organic solar cells (OSCs) by employing a low-temperature evaporable optical spacer, consisting of potassium borohydride (KBH₄) and bathophenanthroline (Bphen) (0:2 : 1, volume ratio). Since the KBH₄-doped Bphen shows improved electron transporting properties and high transparency in the visible range, it can be used as an efficient optical spacer layer that can maximize the internal electrical field distribution in the active layer. As a result, the power conversion efficiency of the OSCs having the KBH₄-doped Bphen with an optimized thickness was improved by 15% in comparison with the device with the non-KBH₄-doped Bphen.