Depleted Heterojunction Photovoltaics with Dual-Shell Nanoparticles
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Solution Overview
Problem
Colloidal quantum dot photovoltaics face limitations in achieving high power conversion efficiencies due to low short-circuit current density (Jsc) in cells sensitized by quantum dots and suboptimal open-circuit voltage (Voc) and fill factor (FF) in Schottky devices.
Innovation Solution
A depleted heterojunction is created by pairing a layer of light-harvesting nanoparticles with an electron-accepting material, where the junction is substantially depleted of free electrons and holes, using materials with different bandgap magnitudes, and employing dual-shell-passivated quantum dots to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If colloidal quantum dots are used as light-harvesting material with solution processing, then manufacturing cost is reduced, but short-circuit current density and power conversion efficiency remain limited
Solution Approach 1:
The patent combines colloidal quantum dots with a metal oxide electron-accepting layer to form a composite heterojunction structure. This composite approach allows the quantum dots to maintain their solution-processable advantage while the metal oxide layer provides efficient electron transport and extraction, thereby achieving both low-cost manufacturing and improved short-circuit current density.
Solution Approach 2:
The metal oxide layer serves as an intermediary between the quantum dot light-harvesting layer and the electrode. It mediates electron transport from the quantum dots to the electrode, improving electron extraction efficiency and reducing recombination losses, which directly enhances short-circuit current density while maintaining the solution processing benefit.
2Power
If Schottky junctions are used with quantum dots, then open-circuit voltage is improved, but fill factor remains suboptimal
Solution Approach 1:
The patent changes the material parameters of the electron-accepting layer from traditional Schottky contact metals to metal oxides with appropriate band structures. This parameter change optimizes both the open-circuit voltage through proper band alignment and the fill factor through improved charge transport properties and reduced interface recombination.
Solution Approach 2:
The patent creates a depleted heterojunction region at the interface between quantum dots and metal oxide, where the local electronic structure is optimized for charge separation. The depletion region provides localized high-quality interfaces that simultaneously support high open-circuit voltage and good fill factor by reducing recombination at the junction.
3Power
If quantum dot photovoltaic cells are sensitized with thin layers, then open-circuit voltage increases, but short-circuit current density decreases
Solution Approach 1:
The metal oxide layer acts as an intermediary that enables thin quantum dot layers to maintain high open-circuit voltage while achieving high short-circuit current density. The metal oxide provides efficient electron transport pathways that compensate for the reduced light absorption in thin layers, allowing both parameters to be optimized simultaneously.
Solution Approach 2:
The patent changes the electron transport parameters by introducing metal oxide with high electron mobility and appropriate conduction band alignment. This parameter change allows thin quantum dot layers to achieve both high open-circuit voltage through proper band offset and high short-circuit current density through efficient electron extraction.
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
This approach significantly enhances photovoltaic device performance by reducing recombination, improving carrier mobility, and minimizing defects, resulting in higher power conversion efficiencies and stability.
Implementation Method 1
Solar cells that generate electricity through the photovoltaic effect
Implementation Method 2
The depletion arises from charge transfer from the electron-accepting contact to the nanoparticles
Data Source
AI summary
Photovoltaic cells are fabricated in which the compositions of the light-absorbing layer and the electron-accepting layer are selected such that at least one side of the junction between these two layers is substantially depleted of charge carriers, i.e., both free electrons and free holes, in the absence of solar illumination. In further aspects of the invention, the light-absorbing layer is comprised of dual-shell passivated quantum dots, each having a quantum dot core with surface anions, an inner shell containing cations to passivate the core surface anions, and an outer shell to passivate the inner shell anions and anions on the core surface.