Ionically gated perovskite solar cell with tunable carbon nanotube interface at thick fullerene electron transporting layer: comparison to gated OPV

TL;DR

This paper presents an ionically gated perovskite solar cell with a thick fullerene ETL and a porous CNT cathode, demonstrating significant efficiency improvements through electrochemical doping and interface tuning, with stability advantages over traditional cathodes.

Contribution

It introduces a novel ionically gated architecture with a thick fullerene ETL and CNT cathode, showing enhanced performance and stability in perovskite solar cells compared to prior designs.

Findings

Efficiency increased from 3% to 11% due to gating-induced doping.

Gating tunes the CNT Fermi level and reduces ETL barrier.

Voc remains unaffected by gating, indicating internal junction control.

Abstract

We demonstrate an ionically gated planar PS-PV solar cell with ultra-thick fullerene ETL with a porous CNT electron collector on top of it. Perovskite photovoltaic devices usually have undoped electron transport layers, usually thin like C60 due to its high resistance. Metallic low work function cathodes are extremely unstable in PS-PV due to reaction with halogens I-/Br-, and it would be desirable to have stable carbon cathodes on top of thick low resistance ETL for enhancing the stability of PS-PVs. We show that gating such top CNT cathode in ionic liquid, as part of a supercapacitor charged by Vg tunes the Fermi level of CNT by EDL charging, and causes lowering of a barrier at of C60/C70 ETL. Moreover, at higher gating voltage ions further propagates into fullerene by electrochemical n-doping, which increases dramatically PV performance by raising mostly two parameters: Isc and FF, resulting in PCE efficiency raised from 3 % to 11 %. N-doping of ETL strongly enhances charge collection by ETL and CNT raising Isc and lowering series resistance and thus increasing strongly PCE. Surprisingly Voc is not sensitive in PS-PV to external Vg gating, on the contrary, to strongly enhanced Voc in ionically gated organic PV, where it is the main gating effect. This insensitivity of Voc to lowering of the work function of Vg gated CNT electrode is a clear indication that Voc in PS-PV is determined by inner p-i-n junction formation in PS itself, via accumulation of its intrinsic mobile ionic species halogens and cations and their vacancies.