title: Neat C₇₀-based bulk-heterojunction polymer solar cells with excellent acceptor dispersion.
abstract: The replacement of common fullerene derivatives with neat-C70 could be an effective approach to restrain the costs of organic photovoltaics and increase their sustainability. In this study, bulk-heterojunction solar cells made of neat-C70 and low energy-gap conjugated polymers, PTB7 and PCDTBT, are thoroughly investigated and compared. Upon replacing PC70BM with C70, the mobility of positive carriers in the donor phase is roughly reduced by 1 order of magnitude, while that of electrons is only slightly modified. It is shown that the main loss mechanism of the investigated neat-C70 solar cells is a low mobility-lifetime product. Nevertheless, PCDTBT:C70 devices undergo a limited loss of 7.5%, compared to the reference PCDTBT:PC70BM cells, reaching a record efficiency (4.44%) for polymer solar cells with unfunctionalized fullerenes. The moderate efficiency loss of PCDTBT:C70 devices, due to an unexpected excellent miscibility of PCDTBT:C70 blends, demonstrates that efficient solar cells made of neat-fullerene are possible. The efficient dispersion of C70 in the PCDTBT matrix is attributed to an interaction between fullerene and the carbazole unit of the polymer.
authors.affiliation: Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche , via P. Gobetti 101, I-40129 Bologna, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Gasparini
authors.forename: Sara
authors.initials: S
authors.lastname: Righi
authors.forename: Francesca
authors.initials: F
authors.lastname: Tinti
authors.forename: Alberto
authors.initials: A
authors.lastname: Savoini
authors.forename: Alessandra
authors.initials: A
authors.lastname: Cominetti
authors.forename: Riccardo
authors.initials: R
authors.lastname: Po
authors.forename: Nadia
authors.initials: N
authors.lastname: Camaioni
keywords: carbazole; conjugated polymers; fullerene; neat C70; organic solar cells