Polymer Solar Cell Reverse-Bias Sweeps for Burn-In Degradation
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Solution Overview
Problem
Polymer solar cells, such as PCDTBT:PC70BM, experience rapid degradation due to photo-induced burn-in losses, leading to inefficient power conversion efficiency (PCE) and short lifetimes, which is a significant barrier to commercial adoption.
Innovation Solution
Applying a reverse bias voltage during current-voltage sweeps intermittently helps to de-trap charge carriers, reducing the series resistance and slowing down the degradation process, thereby extending the lifespan and efficiency of solar cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If polymer solar cells are operated under light exposure, then power conversion efficiency is achieved, but photo-induced burn-in loss occurs causing rapid PCE degradation
Solution Approach 1:
The patent applies periodic reverse bias voltage sweeps at specific intervals (e.g., every 30 minutes to several hours) during light exposure to mitigate photo-induced degradation. This periodic electrical stress resets the energetic disorder in the active layer, preventing accumulation of sub-bandgap states that would otherwise cause continuous PCE decay during operation.
2Power
If high efficiency polymer solar cells are developed, then PCE comparable to a-Si cells is achieved, but rapid PCE degradation prevents commercial adoption
Solution Approach 1:
The patent performs preliminary reverse bias voltage treatment during initial device operation to prevent degradation before it becomes severe. By applying reverse sweeps early in the device lifetime, the method proactively resets charge carrier traps and energetic disorder, extending the functional lifetime of high-efficiency polymer solar cells without compromising their initial PCE performance.
3Reliability
If reverse bias voltage is applied continuously, then charge carrier de-trapping is maximized, but excessive energy consumption and potential device damage occur
Solution Approach 1:
The patent employs periodic rather than continuous reverse bias voltage application, with intervals ranging from minutes to hours between sweeps. This periodic approach maintains charge carrier mobility by periodically resetting energetic disorder while minimizing energy consumption and avoiding continuous electrical stress that could damage the active layer or electrodes.
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 method significantly reduces PCE decay by maintaining charge carrier mobility and inhibiting the formation of defects, resulting in a longer device lifetime and improved performance under simulated real-world exposure.
Implementation Method 1
Applying a reverse bias voltage during current-voltage sweeps intermittently helps to de-trap charge carriers, reducing the series resistance
Implementation Method 2
Photovoltaic solar cells have received a great deal of attention in industrial and research contexts over the past several decades
Data Source
AI summary
Methods and systems for reducing solar cell degradation are provided. The methods and systems related to frequently applying large reverse bias current-voltage (J-V) sweeps to the cell to reduce the rates of internal degradation of the solar cells. The frequent sweeps serve to detrap charge carriers formed in the cell due to photo-oxidative damage. This detrapping reduces the rate of power conversion efficiency (PCE) degradation throughout the life of the solar cell.