Anomalous Charge‐Extraction Behavior for Graphene‐Oxide (GO) and Reduced Graphene‐Oxide (rGO) Films as Efficient p‐Contact Layers for High‐Performance Perovskite Solar Cells

Abstract

Reduced graphene oxides (rGO) are synthesized via reduction of GO with reducing agents as a hole‐extraction layer for high‐performance inverted planar heterojunction perovskite solar cells. The best efficiencies of power conversion (PCE) of these rGO cells exceed 16%, much greater than those made of GO and poly(3,4‐ethenedioxythiophene):poly(styrenesulfonate) films. A flexible rGO device shows PCE 13.8% and maintains 70% of its initial performance over 150 bending cycles. It is found that the hole‐extraction period is much smaller for the GO/methylammonium lead‐iodide perovskite (PSK) film than for the other rGO/PSK films, which contradicts their device performances. Photoluminescence and transient photoelectric decays are measured and control experiments are performed to prove that the reduction of the oxygen‐containing groups in GO significantly decreases the ability of hole extraction from PSK to rGO and also retards the charge recombination at the rGO/PSK interface. When the hole injection from PSK to GO occurs rapidly, hole propagation from GO to the indium‐doped tin oxide (ITO) substrate becomes a bottleneck to overcome, which leads to a rapid charge recombination that decreases the performance of the GO device relative to the rGO device.

Reduced Graphene Oxide as a Stabilizing Agent in Perovskite Solar Cells

“…A suitable HTM should meet certain application requirements, such as effective hole mobility, as well as compatible valence‐band energy level to perovskite absorption material. Moreover, it should display sufficient solubility for solution‐processing and thin‐film formation, appropriate transparency in the visible region, and a modest cost . Several HTMs were found suitable for the fabrication of PSCs, which involves either inorganic (e.g., CuI, CuSCN, and NiO) or organic materials, such as poly(3‐hexythiophen‐2,5‐diyl) (P3HT), PTAA, and poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) .…”

“…However, the effect of rGO on the stability of this architecture was not investigated . Alternatively, Jokar et al employed flexible rGO nanosheets deposited on an ITO substrate as an HTM in an inverted planar heterojunction PSC and demonstrated efficiencies exceeding 16%, which was comparatively higher than the devices containing GO and PEDOT:PSS films . Moreover, a superior stability has been presented, while a flexible rGO device displayed a PCE of 13.8%, and maintained 70% of its initial performance over 150 bending cycles.…”

Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p‐Contact Electrodes for Inverted Planar Perovskite Solar Cells

“…A suitable HEL material for an inverted PHJ device should have the following characteristics: i) effective hole mobility, ii) a compatible energy level matching the valence‐band (VB) level of a perovskite, iii) excellent film formation from a solution‐based process, iv) great transparency in the visible and near infrared regions, and v) cost‐effective production of the material itself. Carbon‐based nanomaterials such as carbon nanotubes, graphene oxide (GO), and reduced graphene oxide (rGO) have recently been reported as an efficient HEL for an inverted PHJ PSC.…”

Introduction of Graphene Nanofibers into the Perovskite Layer of Perovskite Solar Cells

“…[11] Recently,t he application of graphene-derived nanomaterials in PSCs has been studied. [7,[20][21][22][23] Reduced graphene oxide (RGO), [6,[24][25][26][27][28][29][30] graphene quantum dots (GQDs), [11,31] or fullerene, [28] have been used as an interlayer between the ETL/HTL and the perovskite layer,o r being incorporated within the ETL/HTL scaffold to improvet he charge-transport efficiency for mesoporousP SCs. [12][13][14][15][16][17][18][19] Both the electronic structures of the variousinterfaces and the morphology in PSCs can affect the charge carrier transport properties.…”

“…[12][13][14][15][16][17][18][19] Both the electronic structures of the variousinterfaces and the morphology in PSCs can affect the charge carrier transport properties. [7,[20][21][22][23] Reduced graphene oxide (RGO), [6,[24][25][26][27][28][29][30] graphene quantum dots (GQDs), [11,31] or fullerene, [28] have been used as an interlayer between the ETL/HTL and the perovskite layer,o r being incorporated within the ETL/HTL scaffold to improvet he charge-transport efficiency for mesoporousP SCs. In another case, the graphene-derived nanomaterials have been used as top electrode for the PSC to provide efficient charget rans-fer.…”