Lead contamination and intrinsic instability of lead-based perovskite materials greatly limit their application in reliable and scalable manner, and the development of efficient and stable lead-free alternatives is highly desirable....
Poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) represents the state‐of‐the‐art hole transport material (HTM) in inverted perovskite solar cells (PSCs). However, unsatisfied surface properties of PTAA and high energy disorder in the bulk film hinder the further enhancement of device performance. Herein, a simple small molecule 10‐(4‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)phenyl)‐3,7‐bis(4‐vinylphenyl)‐10H‐phenoxazine (MCz‐VPOZ) is strategically developed for in situ fabrication of polymer hole conductor (CL‐MCz) via a facile and low‐temperature cross‐linking technology. The resulting polymer CL‐MCz offers high energy ordering and improved electrical conductivity, as well as appropriate energy‐level alignment, enabling efficient charge carrier collection in the devices. Meanwhile, CL‐MCz synchronously provides satisfied surface wettability and interfacial functionalization, facilitating the formation of high‐quality perovskite films with fewer bulk iodine vacancies and suppressed carrier recombination. Significantly, the device with CL‐MCz yields a champion efficiency of 23.9% along with an extremely low energy loss down to 0.41 eV, which represents the highest reported efficiency for non‐PTAA‐based polymer HTMs in inverted PSCs. Furthermore, the corresponding unencapsulated devices exhibit competitive shelf‐life stability under various operational stressors up to 2500 h, reflecting high promises of CL‐MCz in the scalable PSC application. This work underscores the promising potential of the cross‐linking approach in preparing low‐cost, stable, and efficient polymer HTMs toward reliable PSCs.
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.
Chemical dopants are often required
in organic hole transport materials
(HTMs) to enhance the film conductivity and power conversion efficiency
(PCE) of solar cells. Although additives (LiTFSI + tBP) and oxidants
(FK209) are key dopants in HTMs, their hygroscopic and volatile nature
induce severe morphology change, ion accumulation, as well as perovskite
corrosion, which significantly hinder PSC stability. Various dopant
structures and compositions have been developed, but challenges remain
in fundamentally understanding their complementary effects and individual
roles of additives and oxidants in PSCs. In this study, dopants with
different configurations were investigated thoroughly toward optimizing
the device efficiency and stability. The results show that the additives
LiTFSI + tBP play more essential roles in enhancing the spiro-OMeTAD
(Spiro) conductivity and device efficiency, even though the oxidant
FK209 produces more Spiro+ cations. Consequently, the cooperative
effects of additives and oxidants enable the highest conductivity
(2 × 10–5 S cm–1) and a PCE
of over 21% compared to their individual counterparts. The additives
LiTFSI + tBP exhibit deleterious influences on film stability under
different environmental conditions, whereas FK209-only devices significantly
alleviate these negative effects on device stability, meanwhile achieving
a satisfied conductivity (5 × 10–6 S cm–1) and a high PCE of 19.6%. Besides, unencapsulated
FK209 devices exhibit remarkable environmental and operational stability.
Our work provides new insights into understanding dopants’
roles in charge conduction and offers new doping approaches for organic
semiconductors.
The state-of-the-art electron transport materials (ETMs) in n-i-p PSCs strongly rely on inorganic metal oxides (e.g. TiO2), but they often require high-temperature fabrication and complicated manufacturing. Moreover, little attention has...
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