Pyridine‐functionalized fullerene derivative as an independent electron transport layer enabling efficient and hysteresis‐free regular perovskite solar cells

Abstract

Suitable electron transport materials bearing good interfacial contact, improved electron transport ability, and matched energy levels are indispensable for developing efficient perovskite solar cells (PSCs). Herein, regular (n-i-p) planar Cs 0.05 FA 0.83 MA 0.12 PbI 2.55 Br 0.45 (CsFAMA) PSC devices were fabricated using a pyridine-functionalized fullerene derivative (C 60 -3-BPy) as an independent electron transport layer (ETL), delivering a decent power conversion efficiency (PCE) of 18.22%, which is dramatically higher than that of the control device based on [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) ETL (15.70%). The energy level offset between C 60 -3-BPy and the perovskite is smaller than that based on PCBM ETL, which is beneficial for efficient ohmic contact in ETL/perovskite interface and improved open-circuit voltage (V oc ). Moreover, C 60 -3-BPy affords strong coordination interactions with perovskite, leading to an improved film quality of the perovskite layer with enlarged grain size and decreased trap state density, which contribute to facilitated electron extraction as reflected by the increases of both the fill factor (FF) and the short-circuit current (J sc ). C 60 -3-BPyfacilitated electron extraction further results in hysteresis-free devices.

Recent Advances in Functionalized Fullerenes in Perovskite Solar Cells†

“…Moreover, the strong coordination interactions of C 60 -3-BPy and perovskite lead to an improved film quality of the perovskite film with enlarged grain size and decreased trap state density, consequently contributing to the facilitated electron extraction. [30] Xie et al reported a multiadduct fullerene electron extractor, named hexakis[di(ethoxycarbonyl)methano]-C 60 (HEMC in Figure 1), which was applied as the ETL of inverted PSCs to enhance the photovoltaic performance, including PCEs of 18.93% (champion PCE of 19.53%) in MAPbI 3 -based PSCs, 19.14% (champion PCE of 20. 2%) in the MAPbI x Cl 3-x -based PSCs and 19.21% (champion PCE of 19.98%) in the CsFAMAPbIBr-based PSCs.…”

“…Moreover, the strong coordination interactions of C 60 ‐3‐BPy and perovskite lead to an improved film quality of the perovskite film with enlarged grain size and decreased trap state density, consequently contributing to the facilitated electron extraction. [ 30 ]…”