Non-toxic and earth-abundant V–VI–VII semiconductors for solar cells

Contributed presentation at the EMRS Spring 17 conference in Strasbourg.

Transcript

1. E-mail: alex.ganose.10@ucl.ac.uk @alexganose Non-toxic and earth-abundant V–VI–VII semiconductors for solar cells Alex Ganose, Saya Matsumoto, Keith Butler, Aron Walsh, and David Scanlon Department of Chemistry, University College London Diamond Light Source Ltd. &
2. The inexorable rise of MAPbI3 MAPbI3 is a superstar solar absorber Ganose, Savory and Scanlon, Chem. Commun. (2017), 53, 20–44
3. Desired properties of solar absorbers Other ns2 materials show excellent properties Ganose, Savory and Scanlon, Chem. Commun. (2017), 53, 20–44
4. Beyond MAPbI3 MAPbI3 is extremely efficient but unstable Issue over environmental contamination by toxic Pb Cost analysis indicates 20 yr. lifetime needed for viability Bi3+ confers similar properties but is non-toxic Chang, Ho-Baillie et al., Prog. Photovolt. (2017), 25, 390–405
5. V–VI–VII Materials (Bismuth Chalcohalides) Entire family of BiChX materials exists: – BiOX (X = Cl, Br, I) are great photocatalysts – BiTeX show Rashba splitting & other exotic quantum effects – BiSI & BiSeI are semiconductors w. band gaps ~1.5 eV
6. BiSI & BiSeI BiSI & BiSeI as candidate solar absorbers: – Earth-abundant & non-toxic – Band gaps of 1.57 & 1.29 eV – 1D Ribbon structure BiSI–BiSeI alloy devices performed poorly (< 1%)
7. Electronic Structure 7 BiSI Eg ind = 1.78 eV me = 1.2 m0 mh = 0.4 m0 εr = 37 BiSeI Eg ind = 1.52 eV me = 0.5 m0 mh = 0.3 m0 εr = 36 Band gaps overestimated w.r.t. experiment (temp effects?) Ganose, Butler, Walsh, and Scanlon, J. Mater. Chem. A (2016), 4, 2060–2068
8. Band Alignments Mullins used FTO and CuSCN as the TCO and the HTM Calculations show that they are not ideal, and likely a source of the low efficiency Predict ITO and F8 (poly-fluorene-2,7-diyl) as alternative contacts Ganose, Butler, Walsh, and Scanlon, J. Mater. Chem. A (2016), 4, 2060–2068
9. Phase Stability Ganose, Matsumoto, and Scanlon, in prep
10. Defect Chemistry – BiSI Deep n and p- type defects: – BiI and BiS are ultra deep acceptors – Donor IS is relatively shallow – Compensated by SI EF trapped in the band gap Ganose, Matsumoto, and Scanlon, in prep
11. Defect Chemistry – BiSeI Similar to BiSI defects – SeI is lower energy acceptor but deeper due to size mismatch – n-type defects slightly shallower due to lower CBM EF again trapped mid gap Ganose, Matsumoto, and Scanlon, in prep
12. Conclusions BiSI and BiSeI earth-abundant & non-toxic PV candidates Possess suitable electronic structure, w. small difference between direct and indirect band gaps Small effective masses and high dielectric constants beneficial for PV applications Band misalignments cause of poor device performance? Best suited to p–i–n solar cell architecture
13. Acknowledgements People: • Saya Matsumoto, Dr. David Scanlon (UCL) • Prof. Aron Walsh, Dr. Jarvist Frost (Imperial) • Dr. Keith Butler (Bath) Compute Resources: • Legion & Grace (UCL) • Archer (EPSRC)