Origin of photovoltaic losses in selenium solar cells with open-circuit voltages approaching 1 V

Abstract

Research on selenium solar cells is regaining momentum due to the exciting prospect of integrating a single-element, wide-bandgap (≈1.95 eV) photoabsorber in tandem with a lower bandgap photovoltaic device. Low...

Selenium Thin-Film Solar Cells with Cadmium Sulfide as a Heterojunction Partner

“…Specifically, the devices using fluorine doped tin oxide (FTO) instead of ITO show no S-shaped kink in the J-V curve, which indicates that the carrier transport barrier could be attributed to the ZnMgO/TCO-interface. ZnMgO was first suggested for use in selenium thin-film solar cells by Todorov et al, 27 and later played a key role in achieving the record opencircuit voltage of V oc =0.99 V. 23 However, all ZnMgO-based selenium solar cells reported in literature have been synthesized on FTO-coated glass, whereas the devices fabricated on ITO use TiO 2 instead of ZnMgO as the n-type contact material. 26,33 To investigate the sensitivity towards the choice of TCO, we synthesize ZnMgO, TiO 2 and poly-Se thin-films and examine their relative energy band positions.…”

“…This point is consistent with our previous publications on improving the optoelectronic quality of the selenium absorber. 20,23 However, prior to undertaking elaborate efforts in defect-engineering of selenium, it is essential to determine the appropriate substrate materials on which to grow the absorber. The results of this work demonstrate the significant impact of using ITO instead of FTO.…”

“…[15][16][17][18][19][20] This inorganic semiconductor has a reported direct bandgap between 1.8 and 2.0 eV in its trigonal phase, which may be tuned within the range of 1.2-1.8 eV through alloying with tellurium. 21,22 Furthermore, selenium features a very high absorption coefficient (>10 5 cm -1 ) in the visible region, 23 long-term air-stability, 24,25 and its single-element composition and low melting point of 220 • C makes processing simple, potentially low cost, and compatible with most bottom cells. Nevertheless, the research progress on selenium plateaued with an efficiency record of PCE=5.0% achieved by Nakada et.…”

Laser-Annealing and Solid-Phase Epitaxy of Selenium Thin-Film Solar Cells

“…Laser-annealing is a compelling alternative to thermal annealing, as the energy induced upon exposure may be accurately localized in time and space. , This enables excellent control of the crystallization process as well as the crystal growth direction. The latter is particularly important in the case of trigonal selenium, as the optoelectronic material properties are anisotropic . The crystallographic orientation of the grains in the selenium thin-film is therefore expected to affect the PV device performance.…”

“…The latter is particularly important in the case of trigonal selenium, as the optoelectronic material properties are anisotropic. 14 The crystallographic orientation of the grains in the selenium thin-film is therefore expected to affect the PV device performance. The crystallization of amorphous selenium under the influence of light was first studied half a century ago, where it was observed that illumination increases the growth rate of crystallites and modifies their external morphology.…”