Yan'an University researchers have developed a surface modulation strategy using graphite fluorinated polymers (GFPs) to improve both the efficiency and stability of carbon-based perovskite solar cells (PSCs), addressing persistent challenges related to defect density and film quality in perovskite absorbers.
Carbon-based PSCs (C-PSCs) are particularly attractive due to their low cost, chemical stability, and hydrophobic nature. However, device performance remains highly sensitive to film quality, with defects, moisture sensitivity, and interfacial recombination limiting both efficiency and long-term stability. In this work, GFPs are introduced as a surface functional layer on methylammonium lead iodide (MAPbI3) perovskite films. The approach combines defect passivation, energy level modulation, and crystallization control. The fluorine groups in GFPs exhibit strong electronegativity and interact preferentially with undercoordinated Pb2+ ions, effectively reducing trap states at the film surface. This interaction suppresses non-radiative recombination and contributes to improved charge transport.
A key outcome of the GFP treatment is the promotion of secondary grain growth at the perovskite surface. This process leads to significantly enlarged grain sizes and improved film fusion, reducing grain boundaries that typically act as recombination centers. At the same time, the GFP layer induces a shift in the perovskite energy band structure, which facilitates more efficient surface charge extraction.
The GFPs also spontaneously accumulate at the top interface of the perovskite layer, forming a hydrophobic dipole layer. This interfacial layer serves two critical functions: it enhances charge extraction at the perovskite/carbon interface and improves environmental stability by limiting moisture ingress. Additionally, the dipole effect contributes to favorable energy level alignment, further supporting carrier transport.
Devices fabricated with the structure ITO/SnO2/perovskite/GFPs/carbon achieved a PCE of 18.35% (reverse scan), representing the highest reported efficiency for carbon electrode MAPbI3-based PSCs in this configuration. Stability testing showed that unencapsulated devices retained 77.64% of their initial efficiency after 1200 hours under ambient conditions (25–35% humidity, room temperature), highlighting the effectiveness of the hydrophobic surface layer.
Mechanistically, the performance improvements arise from a combination of factors: strong coordination between fluorine groups and Pb2+ defects, reduced defect density, enhanced crystallinity through secondary growth, optimized energy level alignment, and suppressed ion migration. Together, these effects demonstrate how synergistic surface passivation and crystallization control can overcome key limitations in perovskite film quality.
This work provides a practical pathway for integrating surface-functional polymers to regulate both the electronic structure and morphology of perovskite films, offering an interesting direction for advancing efficient and stable carbon-based perovskite solar cells.
