Accomplishment of Multifunctional π‑Conjugated Polymers by Regulating the Degree of Side-Chain Fluorination for Efficient Dopant-Free Ambient-Stable Perovskite Solar Cells and Organic Solar Cells
journal contributionposted on 26.09.2017, 00:00 by Kakaraparthi Kranthiraja, Sang Ho Park, Hyunji Kim, Kumarasamy Gunasekar, Gibok Han, Bumjoon J. Kim, Chang Su Kim, Soohyun Kim, Hyunjung Lee, Ryosuke Nishikubo, Akinori Saeki, Sung-Ho Jin, Myungkwan Song
We present an efficient approach to develop a series of multifunctional π-conjugated polymers (P1–P3) by controlling the degree of fluorination (0F, 2F, and 4F) on the side chain linked to the benzodithiophene unit of the π-conjugated polymer. The most promising changes were noticed in optical, electrochemical, and morphological properties upon varying the degree of fluorine atoms on the side chain. The properly aligned energy levels with respect to the perovskite and PCBM prompted us to use them in perovskite solar cells (PSCs) as hole-transporting materials (HTMs) and in bulk heterojunction organic solar cells (BHJ OSCs) as photoactive donors. Interestingly, P2 (2F) and P3 (4F) showed an enhanced power conversion efficiency (PCE) of 14.94%, 10.35% compared to P1 (0F) (9.80%) in dopant-free PSCs. Similarly, P2 (2F) and P3 (4F) also showed improved PCE of 7.93% and 7.43%, respectively, compared to P1 (0F) (PCE of 4.35%) in BHJ OSCs. The high photvoltaic performance of the P2 and P3 based photovotaic devices over P1 are well correlated with their energy level alignment, charge transporting, morphological and packing properties, and hole transfer yields. In addition, the P1–P3 based dopant-free PSCs and BHJ OSCs showed an excellent ambient stability up to 30 days without a significant drop in their initial performance.