ZnCdS Window Layer for Photovoltaic Devices
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Solution Overview
Problem
Conventional photovoltaic devices suffer from inefficient energy conversion and complex manufacturing processes, with cadmium sulfide's low bandgap leading to current loss and issues like shunting, and harsh processing conditions affecting thermal stability.
Innovation Solution
A photovoltaic device with a transparent window layer comprising cadmium sulfide and oxygen, deposited using a pulsed direct current plasma sputtering method, which enhances the fill factor to greater than 0.65 and improves thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If cadmium sulfide is used to make the window layer, then optical loss by absorption is reduced, but current loss and shunting issues occur due to low bandgap
Solution Approach 1:
The patent changes the compositional parameters of the window layer by incorporating zinc into cadmium sulfide to form ZnCdS. This alloying modifies the bandgap and electrical properties, reducing shunting while maintaining optical absorption performance. The gradual transition from pure CdS to ZnCdS represents a parameter change strategy to resolve the contradiction between optical loss reduction and current loss prevention.
Solution Approach 2:
The patent creates a composite material system by combining zinc sulfide and cadmium sulfide in the window layer. This composite approach allows tuning of both optical and electrical properties simultaneously. The ZnCdS composite provides higher bandgap than pure CdS, reducing shunting, while maintaining sufficient absorption for optical performance.
2Reliability
If a high resistive transparent buffer layer is employed to prevent shunting, then device reliability improves, but device complexity increases
Solution Approach 1:
The patent merges the window layer and buffer layer functions into a single ZnCdS layer. This layer simultaneously provides optical transparency, absorption, and high resistance to prevent shunting. By combining multiple functions into one layer, the device structure is simplified while maintaining reliability, eliminating the need for separate buffer layers.
Solution Approach 2:
The ZnCdS window layer is designed to perform multiple functions: it serves as the optical window, the absorption layer, and the high-resistance buffer all in one. This multi-functional design reduces device complexity while ensuring shunting prevention, as the same layer provides both optical and electrical performance.
3Ease of manufacture
If conventional sputtering methods are used, then manufacturing process is simple, but thermal stability of layers at high temperatures is compromised
Solution Approach 1:
The patent employs pulsed direct current (pulsed DC) sputtering instead of continuous DC sputtering. This periodic deposition method allows better control of film formation, creating denser and more thermally stable layers. The pulsed nature enables proper adatom migration and film densification during deposition, improving thermal stability while maintaining manufacturing feasibility.
Solution Approach 2:
The patent changes the deposition parameters by using pulsed DC power instead of continuous DC, and by controlling oxygen partial pressure during sputtering. These parameter changes result in films with improved thermal stability. The pulsed deposition allows better film density and crystallinity, making the layers resistant to thermal degradation at high processing temperatures.
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 improved energy conversion efficiency and thermal stability, reducing current loss and shunting issues, while simplifying the manufacturing process by incorporating cadmium sulfide and oxygen in the window layer.
Implementation Method 1
applying a plurality of direct current pulses to the target to create a pulsed direct current plasma; sputtering the target with the pulsed direct current plasma to eject a material comprising cadmium and sulfur into the plasma; and depositing a film comprising the material onto a substrate
Data Source
AI summary
One aspect of the present invention provides a device that includes a substrate; a first semiconducting layer; a transparent conductive layer; a transparent window layer. The transparent window layer includes cadmium sulfide and oxygen. The device has a fill factor of greater than about 0.65. Another aspect of the present invention provides a method of making the device.