Multi-junction Organic Photovoltaic Cells with Transparent Interconnecting Layer
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Solution Overview
Problem
Small molecule tandem photovoltaic cells face limitations in power conversion efficiency due to narrow absorption range, low VOC, and thermalization energy losses, as well as spectral overlaps and low charge recombination efficiency in conventional designs, which restrict the use of thicker subcells and effective absorption of electromagnetic radiation.
Innovation Solution
A multi-junction photovoltaic device with a donor-acceptor-acceptor molecule structure, specifically using a NIR-absorbing front subcell and a green-absorbing back subcell, along with nanocrystalline planar-mixed heterojunctions, to enhance charge collection length and minimize spectral overlap, combined with a transparent interconnecting layer to maximize photocurrent across a broad absorption spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the photoactive region is thickened to enhance optical absorption, then the absorption of electromagnetic radiation is improved, but the charge collection efficiency deteriorates due to the short exciton diffusion length
Solution Approach 1:
The device is divided into multiple subcells (front subcell, back subcell, and intermediate subcell) with distinct absorption ranges. Each subcell has its own photoactive region with donor-acceptor heterojunction, allowing independent optimization of thickness and charge collection in each segment while collectively achieving broad spectral coverage and high absorption.
2Device complexity
If conventional separating layers are used to separate subcells, then the structural separation is achieved, but the charge recombination efficiency is reduced and spectral overlap increases
Solution Approach 1:
An intermediate subcell is introduced between the front and back subcells, serving as a mediator that absorbs specific wavelength ranges (500-700 nm) and facilitates charge recombination. This intermediate layer prevents direct interaction between front and back subcells, reducing spectral overlap while maintaining efficient charge management through its own donor-acceptor heterojunction structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves power conversion efficiencies of up to 12.0% in four-junction OPVs, significantly improving upon previous efficiencies by optimizing subcell absorption and reducing spectral overlap, thereby enhancing overall energy harvesting.
Implementation Method 1
donor-acceptor-acceptor structure to facilitate strong intramolecular electron transfer leading to large molecular dipole moment thus promoting efficient electron orbital overlap between these molecules in the solid beneficial for charge transport
Implementation Method 2
nanocrystalline planar-mixed heterojunctions (PM-HJ) with the new donor molecule for the sub-cells in the stacks, the PM-HJ has a large charge collection length
Implementation Method 3
multi-junction photovoltaic device with a donor-acceptor-acceptor molecule structure, specifically using a NIR-absorbing front subcell and a green-absorbing back subcell
Data Source
AI summary
A highly efficient multi junction photovoltaic device, such as a two, three, or four junction device, is disclosed. The multi-junction device may include a first subcell comprising a first photoactive region and a second subcell comprising a second photoactive region. The first and second photoactive regions are designed to minimize spectral overlap and maximize photocurrent across a broad absorption spectra, such as wavelengths ranging from 400 nm to 900 nm. The device may further include an inter-connecting layer, disposed between the first subcell and the second subcell, that is at least substantially transparent. By introducing a transparent interconnecting layer, a dual element (tandem) cell achieves a power conversion efficiency of 10.0±0.5%. By adding an additional (3rd) sub-cell that absorbs at the second order optical interference maximum within the stack. The triple junction cell significantly improves the quantum efficiency at shorter wavelengths, achieving a power conversion efficiency of 11.1±0.5%. Adding additional sub-cells has been shown to increase power conversion efficiency above 12%.