Stability of Nonfullerene Organic Solar Cells: from Built‐in Potential and Interfacial Passivation Perspectives

• Published in: Advanced energy materials 2019-05, Vol.9 (19), p.n/a
• Main Authors: Wang, Yiwen, Lan, Weixia, Li, Ning, Lan, Zhaojue, Li, Zhen, Jia, Jingnan, Zhu, Furong
• Format: Article
• Language: English
• Subjects: built‐in potential; charge extraction; Heterojunctions; Interface reactions; Interface stability; interfacial passivation; Molybdenum oxides; Molybdenum trioxide; Organic chemistry; Passivity; Performance degradation; Phase separation; Photovoltaic cells; Solar cells; stability of nonfullerene organic solar cells; Stratification; vertical phase separation; Vertical separation
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201900157

Remarkable progress has been made in the development of high‐efficiency solution‐processable nonfullerene organic solar cells (OSCs). However, the effect of the vertical stratification of bulk heterojunction (BHJ) on the efficiency and stability of nonfullerene OSCs is not fully understood yet. In this work, we report our effort to understand the stability of nonfullerene OSCs, made with the binary blend poly[(2,6‐(4, 8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′] dithiophene‐4,8‐dione)] (PBDB‐T):3,9‐ bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐ dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′] dithiophene (ITIC) system. It shows that a continuous vertical phase separation process occurs, forming a PBDB‐T‐rich top surface and an ITIC‐rich bottom surface in PBDB‐T:ITIC BHJ during the aging period. A gradual decrease in the built‐in potential (V0) in the regular configuration PBDB‐T:ITIC OSCs, due to the interfacial reaction between the poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer and ITIC acceptor, is one of the reasons responsible for the performance deterioration. The reduction in V0, caused by an inevitable reaction at the ITIC/PEDOT:PSS interface in the OSCs, can be suppressed by introducing a MoO3 interfacial passivation layer. Retaining a stable and high V0 across the BHJ through interfacial modification and device engineering, e.g., as seen in the inverted PBDB‐T:ITIC OSCs, is a prerequisite for efficient and stable operation of nonfullerene OSCs. Retaining a stable and high built‐in potential across bulk heterojunction through interfacial modification and device engineering is a prerequisite for efficient and stable operation of nonfullerene organic solar cells.