Challenge:
Decrease Voc deficit of current CZTSSe (1.13 eV) solar cells.
The reported device has 12.6 % efficiency with
500 mV of Voc from a maximum of 820 mV calculated by SQ analysis. Therefore if Voc is enhanced the device would get better. But to achieve this enhancement we should understand the dependence between minority carrier lifetime and recombination process.
Highlights:
- Kesterites are fabricated with Cu-poor and Zn-rich content
- Understand: junction CdS/CZTSSe, current collection and recombination mechanism
- Defects impact the minority carrier lifetime and thus collection length (Lc = Xp + Ln).
- Lifetime (µn, µp, defects)
Characterization Techniques:
- SIMS - Analysis of carbon and oxygen concentration
- SEM - Morphology (Front and cross section)
- EDX - Composition (Cu, Zn, Sn) profiling
- JV - Basic parameters (Voc, Jsc, FF, Eff)
- Sites method: Diode parameter - Ideality factor, Saturation current Jo, Rs, Rsh
- CV - Concentration and nature of defects: Sensitive to interface traps
- DLCP - (Drive level capacitance profile): Sensitive to bulk defects
- JVT - Activation energy of the main recombination process
- EQE - External quantum efficiency: Eg
- UV-VIS-NIR: Optical reflectance
- EBIC - Indicate collection region for minority carriers.
Device fabrication:
- CZTSSe fabricate by pure-solution method (Hydrazine)
- Back contact: Molybdenum (500 nm)
- Mo(S,Se)2: approx (180 nm)
- Absorber: CZTSSe (2 µm)
- Buffer: CdS (25 nm)
- Window: ZnO/ITO (10 nm / 50 nm)
- Grid: Ni/Al (2 µm)
- Anti-reflective: MgF2
- Total area: 0.42 cm2 defined by mechanic scribe
