Enhancing Phonon Group Velocities and Interfacial Heat Conduction for Efficient and Stable Perovskite Solar Cells

The inherently low thermal conductivity of conventional hole-transport layers (HTLs) in inverted perovskite solar cells (PSCs) introduces a substantial discrepancy in interlayer heat-transfer dynamics, leading to detrimental heat accumulation and nonradiative recombination. Herein, we develop a spinel-type semiconductor of CuBi2O4, and integrate it into a composite HTL architecture to regulate heat conduction for the first time. Leveraging enhanced phonon group velocities, the CuBi2O4-based composite HTL achieves exceptional thermal compatibility with the perovskite absorber, demonstrating enhanced heat conduction and optimal thermal-expansion coefficient alignment. These synergistic effects significantly delay hot-carrier relaxation and reduce excess energy dissipation by approximately 10-fold. Consequently, we obtain high-quality perovskite films with ordered orientation and released residual strain, yielding an impressive power conversion efficiency (PCE) of 27.18% (certified 26.83%). Remarkably, these phonon-engineered devices maintain 90.1%, 82.3%, 85.6% and 93.7% of their initial PCEs under ISOS-D-2Ⅰ, ISOS-D-3, ISOS-T-1 and ISOS-L-1 conditions for 2000 h, respectively. Low thermal conductivity of hole-transport layers in perovskite solar cells causes heat buildup, energy loss, and reduced stability. Wu et al. introduce a copper bismuth oxide composite layer to improve heat flow, achieving higher efficiency and long-term device stability.