Evaporated Undoped Spiro‐OMeTAD Enables Stable Perovskite Solar Cells Exceeding 20% Efficiency

Abstract

Thermal evaporation (TE) as a scalable and low‐cost technique for fabrication of organic hole transport materials (HTMs) typically produces low photovoltaic performance and poor device reproducibility in the application of perovskite solar cells (PSCs), and there is a clear need to understand the weaknesses of TE. Here, a versatile manufacturing technology, solvent‐annealing assisted thermal evaporation (SATE), enabling effective modulation of organic film morphology as well as optoelectronic properties, is introduced. The SATE method produces undoped spiro‐OMeTAD layers with high density, good film homogeneity, enhanced conductivity, and remarkable film stability, all of which are superior to that made by conventional TE. In addition, SATE films eliminate the dopant induced degradation mechanism and simultaneously improve the electrical conductivity of undoped HTMs. Significantly, the resulting devices yield a 36% enhancement of power conversion efficiency (PCE) from 14.68% (TE) to 20.02% (SATE), which is the highest reported PCE for evaporated HTMs in n–i–p PSCs. Moreover, unencapsulated PSC devices with SATE demonstrate an impressive environmental and thermal stability by maintaining 85% of initial performance after 2500 h in air with 30% humidity. The high efficiency with simultaneously improved stability demonstrates SATE can be generally applicable to controllable fabrication of organic thin film and reliable devices.

Conjugation Engineering of Spiro-Based Hole Transport Materials for Efficient and Stable Perovskite Solar Cells

“…Due to the favorable properties, high photovoltaic performance has been demonstrated for various spiro-type HTMs. − However, most spiro-type HTMs suffer from low intrinsic hole mobility (<10 –5 cm 2 V –1 s –1 ), and they must be chemically doped to have effective hole extraction capability. , Unfortunately, the hygroscopic nature of the dopants such as lithium salts may cause the degradation of the perovskite and thus reduce the stability of PSCs . Although some excellent works have been done to improve the PCE of undoped Spiro-OMeTAD , or develop new spiro cores , for dopant-free HTMs, there is still an urgent need for a simple but effective strategy to construct spiro-type HTMs with intrinsic high hole mobility and good hydrophobicity. This is crucial for improving the device stability because HTMs with decent hole mobility can be used in dopant-free PSCs and good hydrophobicity of HTM layer is beneficial for protecting the underlying perovskite. , …”

Constructing Molecular Bridge for High-Efficiency and Stable Perovskite Solar Cells based on P3HT Hole Transport Material

“…Besides, the capacitance − frequency plots (Fig. 5c) present a 2 orders of magnitude decrease of capacitance at low frequency for devices with M-P3HT or R-P3HT when comparing with conventional PSC based on P3HT HTM, owing to the fact that MDN brings about an effective defect passivation along with the formation of charge transfer channels, resulting in reducing the charge accumulation at perovskite/HTM interface 25,40 .…”

“…In addition, Zhang et al reported a high PCE, ca. 20%, based on the undoped Spiro-OMeTAD through solvent-annealing assisted thermal evaporation (SATE) 25 . However, this complex evaporation technique is not applicable for most laboratories and the reproducibility still needs veri cation.…”

Spiro‐OMeTAD‐Based Hole Transport Layer Engineering toward Stable Perovskite Solar Cells

“…Reproduced with permission. [100] Copyright 2022, John Wiley and Sons. and enable a fast intramolecular charge transport (Figure 11c).…”

“…Left: with 30% RH for 200 and 1000 h. Right: with 70% RH for 10 and 100 h. c) Shelf stability of the unencapsulated devices prepared via thermal evaporation (TE), SATE, and SP in air conditions with 30% RH at room temperature.The inset shows the MPP tracking in air conditions with 40% RH. Reproduced with permission [100]. Copyright 2022, John Wiley and Sons.…”