Efficient and stable operation of nonfullerene organic solar cells: retaining a high built-in potential†
This work reports our research efforts to improve the operational stability of nonfullerene organic solar cells (OSCs) by retaining a stable and high built-in potential across the bulk heterojunction (BHJ). The stable built-in potential in the OSCs is realized through suppression of the interfacial reaction between the BHJ and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) hole transporting layer (HTL). The impact of interfacial modification, molybdenum oxide (MoO3) induced oxidation doping of the PEDOT:PSS HTL, on the operational stability of poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)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-2F): 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (IT-4F) nonfullerene OSCs has been analyzed. We found that the MoO3-induced oxidation doping in PEDOT:PSS can effectively suppress the interfacial chemical reactions between IT-4F and PEDOT:PSS, a recently identified major degradation mechanism in nonfullerene acceptor (NFA) with 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile moieties-based OSCs. Our findings highlight the importance of retaining high built-in potential to mitigate any associated degradation mechanisms, to accompany the rapid advances in the molecular synthesis of NFAs, toward enhanced operational stability of NFA-based OSCs.