Journal
SUSTAINABLE ENERGY & FUELS
Volume 3, Issue 2, Pages 550-563Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c8se00509e
Keywords
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Funding
- German Federal Ministry of Education and Research (BMBF), within the project Materialforschung fur die Energiewende [03SF0540]
- German Federal Ministry for Economic Affairs and Energy (BMWi) through the PersiST project [0324037C]
- HyPerCells (a Joint Graduate School of the Potsdam University)
- German Research Foundation (DFG) within the collaborative research center 951 Hybrid Inorganic/Organic Systems for Opto-Electronics (HIOS)
- HyPerCells (a Joint Graduate School of the HZB)
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The incorporation of even small amounts of strontium (Sr) into lead-base hybrid quadruple cation perovskite solar cells results in a systematic increase of the open circuit voltage (V-oc) in pin-type perovskite solar cells. We demonstrate via absolute and transient photoluminescence (PL) experiments how the incorporation of Sr significantly reduces the non-radiative recombination losses in the neat perovskite layer. We show that Sr segregates at the perovskite surface, where it induces important changes of morphology and energetics. Notably, the Sr-enriched surface exhibits a wider band gap and a more n-type character, accompanied with significantly stronger surface band bending. As a result, we observe a significant increase of the quasi-Fermi level splitting in the neat perovskite by reduced surface recombination and more importantly, a strong reduction of losses attributed to non-radiative recombination at the interface to the C-60 electron-transporting layer. The resulting solar cells exhibited a V-oc of 1.18 V, which could be further improved to nearly 1.23 V through addition of a thin polymer interlayer, reducing the non-radiative voltage loss to only 110 meV. Our work shows that simply adding a small amount of Sr to the precursor solutions induces a beneficial surface modification in the perovskite, without requiring any post treatment, resulting in high efficiency solar cells with power conversion efficiency (PCE) up to 20.3%. Our results demonstrate very high V-oc values and efficiencies in Sr-containing quadruple cation perovskite pin-type solar cells and highlight the imperative importance of addressing and minimizing the recombination losses at the interface between perovskite and charge transporting layer.
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