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

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.

Automated summary

Solvent-annealing assisted thermal evaporation (SATE) method is introduced to produce undoped spiro-OMeTAD layers with higher density, better film homogeneity, enhanced conductivity, and remarkable stability compared to conventional thermal evaporation (TE). The resulting perovskite solar cells (PSCs) fabricated with SATE exhibit a 36% enhancement in power conversion efficiency (PCE) and impressive environmental and thermal stability.