Periodic Reporting for period 1 - ENLIGHTEN (full harvEst of solar radiatioN using a quantum-dot-in-perovskite absorber and LIGHT managemENt structures)
Reporting period: 2020-12-01 to 2022-11-30
Europe has set the energy transition to renewable sources as a priority policy to minimize the effects of climate change. Photovoltaic (PV) energy is called to play a major role in the world’s electricity production in the mid-term. The present market-dominant technology, crystalline silicon (Si), has reached its practical efficiency record of 26%, and the energy cost of this technology – which has been diminishing in the last decades, following a technology learning curve – seems to be stagnating now. Given the in-creasing fraction of the total cost of PV electricity represented by area-related costs (e.g. encapsulation and field-installation), any improvement in the solar cell’s efficiency will partly translate in a further reduction of the PV electricity price. For this reason, research on new ways of increasing the conversion efficiency of solar cells is still extensive. In parallel, PV is expected to expand in distributed autonomous systems, with thin solar cells supported on a variety of rigid or flexible (e.g. polymers and metal foils) low-cost substrates; thereby fostering a wide range of solar-powered systems for portable electronics, electric cars, medical diagnostic, smart-packaging, etc.
Among the proposed novel concepts for high-efficiency solar cells, the intermediate band solar cell (IBSC) has received great attention by the scientific community. In conventional single-gap solar cells, photons with energy lower than the bandgap of the absorber material are wasted. The IBSC concept allows harvesting below-bandgap photons without voltage loss, which increases the limiting efficiency from 33% to 50%. So far, IBSCs have been realized with epitaxially-grown quantum-dot (QD) super-lattices of III-V semiconductors. However, no pronounced efficiency enhancement has been yet report-ed, since this technological approach is unable to produce nanostructured materials with the required opto-electronic properties. Recently, a new family of semiconductor materials, colloidal QDs in a perovskite host (CQDs@Perovskite), has emerged as a promising way to develop efficient IBSCs. This project’s goal is to exploit CQDs@Perovskite materials combined with microstructure-based light trap-ping to pave the way for low-cost high-efficiency solar cells, compatible with flexible- substrate technology.
Among the proposed novel concepts for high-efficiency solar cells, the intermediate band solar cell (IBSC) has received great attention by the scientific community. In conventional single-gap solar cells, photons with energy lower than the bandgap of the absorber material are wasted. The IBSC concept allows harvesting below-bandgap photons without voltage loss, which increases the limiting efficiency from 33% to 50%. So far, IBSCs have been realized with epitaxially-grown quantum-dot (QD) super-lattices of III-V semiconductors. However, no pronounced efficiency enhancement has been yet report-ed, since this technological approach is unable to produce nanostructured materials with the required opto-electronic properties. Recently, a new family of semiconductor materials, colloidal QDs in a perovskite host (CQDs@Perovskite), has emerged as a promising way to develop efficient IBSCs. This project’s goal is to exploit CQDs@Perovskite materials combined with microstructure-based light trap-ping to pave the way for low-cost high-efficiency solar cells, compatible with flexible- substrate technology.
During the course of the project both theoretical and experimental works were carried out.
In the theoretical part: Photonic structures for integration in perovskite technology were simulated and optimized. Moreover, modelling of IBSCs from a theoretical standpoint confirmed that CQD@Perovskites have potential for high below-bandgap absorption.
In the experimental part: A new setup for the synthesis of CQDs was developed, focusing on the material targeted, lead sulfide (PbS). The process of inclusion of the PbS CQDs in different perovskite hosts was optimized. After exhaustive material characterization (morphological, optical, structural and surface chemical analysis), methylammonium lead iodide (MAPbI3) was chosen as the most adequate host. IBSCs were fabricated, using the optimized PbS@MAPbI3 as absorber material. Opto-electronic characterization of the IBSCs was performed in order to investigate characteristic IBSC behaviour.
The description and results of the project were disseminated both to the scientific community and to the general public. As scientific output, there were 2 journal publications and the participation in 7 international conferences, in addition to several national conferences. As dissemination to the general public, the content and motivation of the project was presented in an informational talk to the Photovoltaic Spanish Technological Platform (Fotoplat), and explained to visiting high-school students during the ‘open-days’ of the host institution.
In the theoretical part: Photonic structures for integration in perovskite technology were simulated and optimized. Moreover, modelling of IBSCs from a theoretical standpoint confirmed that CQD@Perovskites have potential for high below-bandgap absorption.
In the experimental part: A new setup for the synthesis of CQDs was developed, focusing on the material targeted, lead sulfide (PbS). The process of inclusion of the PbS CQDs in different perovskite hosts was optimized. After exhaustive material characterization (morphological, optical, structural and surface chemical analysis), methylammonium lead iodide (MAPbI3) was chosen as the most adequate host. IBSCs were fabricated, using the optimized PbS@MAPbI3 as absorber material. Opto-electronic characterization of the IBSCs was performed in order to investigate characteristic IBSC behaviour.
The description and results of the project were disseminated both to the scientific community and to the general public. As scientific output, there were 2 journal publications and the participation in 7 international conferences, in addition to several national conferences. As dissemination to the general public, the content and motivation of the project was presented in an informational talk to the Photovoltaic Spanish Technological Platform (Fotoplat), and explained to visiting high-school students during the ‘open-days’ of the host institution.
The first prototypes of IBSCs based on PbS CQDs and MAPbI3 perovskite were fabricated. With them, it was demonstrated that the interband thermal escape of charge carrier is strongly suppressed in the CQDs@Perovskite material developed in the project. The inhibition of such process was a long-sought milestone in the IBSC community since it is a requisite for high-efficiency operation. Additionally, the absorption coefficient of below-bandgap photons was measured to be in the order of 103 cm-1, much higher than in previous IBSC attempts, which corroborates experimentally the idea that CQDs@Perovskite are ideal candidates to fabricate high-efficiency IBSCs. The prospective development of such highly-efficient devices would have a great socio-economic impact, as they could be used to reduce the cost of PV electricity as well as to integrate the PV technology in new niche markets, such as those demanding flexible/portable solar cells.