Expanding the absorption of lead-halide perovskites via the inclusion of QDs for enhanced photovoltaic conversion
Iñigo Ramiro a, Ugur Deneb Menda a, Guilherme Ribeiro a, Santanu Jana a, Daniela Nunes a, Elvira Fortunato a, Rodrigo Martins a, Manuel João Mendes a
a Universidade NOVA de Lisboa, CENIMAT-I3N, Faculdade de Ciências e Tecnologia, Portugal
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Iñigo Ramiro, 247
Publication date: 20th April 2022

Due to their favorable opto-electronic properties, lead-halide perovskites (HP) are tremendously investigated as the active layer of optoelectronic devices, with a particular interest in solar cells. In 2015 quantum-dot-in-perovskite (QDiP) solids were demonstrated by embedding PbS quantum dots (QDs) in a MAPbI3 perovskite matrix.[1] Such composite materials exhibit optical properties (absorption and emission) related to both the QDs and the HP matrix. It has been suggested[2,3] that QDiPs can be an ideal material family for implementing the so-called intermediate band solar cell (IBSC), a photovoltaic (PV) concept  that aims at increasing the efficiency of solar cells by up to 50% via the exploitation of below-bandgap absorption.[4] In the QDiP approach to an IBSC, the QDs harvest light below the bandgap of the HP, while the HP absorbs light above its bandgap and provides optimal transport properties for carrier collection. So far, one attempt of QDiP-based IBSC has been made,[5] using PbS QDs embedded in MAPbBr3. This work demonstrated photocurrent due to the absorption in the QDs of photons with an energy below the bandgap of the HP. However, the efficiency of this process was low (quantum efficiency ~10–3), consequent to a weak below-bandgap absorption. For QDiPs to give raise to high-efficiency IBSCs, they must exhibit strong absorptivity, not only in the supra-bandgap region, but in the below-bandgap region too. This requires introducing a high concentration of QDs in the CQiP composite while preserving good structural and optoelectronic properties in the HP matrix, which represents a great technological challenge. In this work, we report the fabrication of PbS@MAPbI3 QDiP films exhibiting high below-bandgap absorption coefficients (>10–3 cm–1) and excellent structural quality.

The thin films were prepared by a solution-based technique by adding the QDs to the HP precursor solution. Previously the QDs had undergone a complete halide ligand-exchange process, verified by FTIR spectroscopy. X-Ray diffractometry patterns confirm the high crystallinity of the MAPbI3 layers, preserved upon inclusion of the QDs. UV-VIS measurements reveal the emergence of below-bandgap absorption, proportional to the QD concentration in the films. Moreover, photoemission of the PbS QDs was also detected, in parallel to a notable intensity reduction in the emission of the HP, suggesting the presence of a charge transfer process from the perovskite host to the QDs. Overall, the optical and structural analyses prove an excellent material quality and present PbS/MAPbI3 QDiP as a premium candidate to realize high-efficiency IBSCs.

The work received funding from the European Union’s Horizon 2020 research and innovation programme under the project ENLIGHTEN (H2020-MSCA-IF-2019, Grant No. 891686) and Synergy (H2020-Widespread-2020-5, CSA) grant agreement No. 952169. The work was also financed by national funds from FCT, I.P., in the scope of the projects LA/P/0037/2020, UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N, and of the project LocalEnergy (PTDC/EAM-PEC/29905/2017).

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