Improved Performance and Stability of Organic Solar Cells by the Incorporation of a Block Copolymer Interfacial Layer

Abstract

good mechanical flexibility, and low-cost fabrication. [1-3] Low power conversion efficiency (PCE), one of the main challenges for OSCs, has been gradually overcome by the synthesis of specifically tuned donor materials [4] such as PTB7, [5] PffBT4T-2OD, [6] PBDTTT-EFT, [7] PBDB-T-Cl, [8] and light absorbing nonfullerene acceptors [9] such as TPB, [10] ITIC, [11] IT-4F, [12] BTPTT-4F, [13] BTP-4Cl, [14] and Y6 [15] achieving PCEs between 10% and 16%. Recently, a PCE of 18.22% for an OSC was reported, clearly demonstrating their promising future. [16] Despite this enticing progress, the relatively low stability of OSCs compared to other commercially available photovoltaic devices such as crystalline silicon remains the major challenge for the successful commercialization of OSC technology. [17-20] Therefore, the development of methodologies that simultaneously improve the efficiency and stability of OSCs can significantly contribute to their progress toward large-scale production. In this proof-ofconcept study, a new approach to achieving this dual aim in OSCs is demonstrated. By specifically designing and incorporating an interfacial block copolymer layer whose two different blocks are selectively compatible with the photoactive layer and In a proof-of-concept study, this work demonstrates that incorporating a specifically designed block copolymer as an interfacial layer between a charge transport layer and the photoactive layer in organic solar cells can enhance the interface between these layers leading to both performance and stability improvements of the device. This is achieved by incorporating a P3HT 50-b-PSS x block copolymer as an interfacial layer between the hole transporting and photoactive layers, which results in the improvement of the interfacial roughness, energy level alignment, and stability between these layers. Specifically, the incorporation of a 10 nm P3HT 50-b-PSS 16 and a 13 nm P3HT 50-b-PSS 23 interfacial layer results in a 9% and a 12% increase in device efficiency respectively compared to the reference devices. In addition to having a higher initial efficiency, the devices with the block copolymer continue to have a higher normalized efficiency than the control devices after 2200 h of storage, demonstrating that the block copolymer not only improves device efficiency, but crucially, prevents degradation by stabilizing the interface between the hole transporting layer and the photoactive layer. This study proves that appropriately designed and optimized block copolymers can simultaneously stabilize and improve the efficiency of organic solar cells.

Recent Advances in Hole-Transporting Layers for Organic Solar Cells

“…PFT-D molecular dipole screened the attraction between PEDOT and PSS chains; additionally, the –SO 3 − ions of PFT-D act as a conjugate base of PSS, improving current generation. Poly(3-hexylthiophene)- b -poly(p-styrenesulfonate) (P3HT 50 -b-PSS 23 ) block polymers were incorporated between HTL PEDOT:PSS and the active-layer P3HT:PCBM [ 287 ]. The OSCs with P3HT-b-PSS interfacial layer improved PCE by 12% due to increased V oc and FF that compensate for the decreased J sc caused by the blocked light irradiance to the P3HT.…”