Enhancing performance and stability of perovskite solar cells using hole transport layer of small molecule and conjugated polymer blend

Here, we develop a method to prepare a dopant-free hole transporting material by blending an organic semiconductor and a conjugated polymer with 1,8-diiodooctane (DIO) additive. The normal-type solar cell based on the hole transporting material (HTM) blend with DIO + PCDTBT shows enhanced efficiency up to 18.0% compared to 14.7% for the device using the pristine small molecule. Incorporation of DIO results in increased crystallinity, while the conjugated polymer induces an intermolecular network for efficient charge transport with improved film morphology. Consequently, the HTM blend with DIO + PCDTBT shows a higher hole mobility and more efficient charge transfer at the perovskite/hole transporting layer interface compared with the pristine HTM. Furthermore, the solar cell introducing the HTM blend with DIO shows high mechanical and moisture stability; the compact and homogeneous film of high crystalline HTM shows more adhesive contact with perovskite and effectively prevents the penetration of moisture. The efficiency of the unencapsulated device using a small molecular HTM decreases to 60%, whereas the corresponding device with HTM blend maintains 80% performance after storage under 85% relative humidity and 85 °C.