Device Characteristics of CZTSSe Thin‐Film Solar Cells with 12.6% Efficiency

Abstract

The thin-fi lm photovoltaic material Cu 2 ZnSnS x Se 4-x (CZTSSe) has drawn world-wide attention due to its outstanding performance and earth-abundant composition. Until recently, [ 1 ] stateof-the-art CZTSSe thin-fi lm solar cells were limited to 11.1% power conversion effi ciency (PCE), with these performance levels being achieved via a hydrazine slurry approach. [ 2 ] Other vacuum-and non-vacuum-based deposition techniques have also been successful in fabricating CZTSSe solar cells with PCE above 8%. [ 3,4 ] However, even record devices with PCE of 11% are still far below the physical limit, known as the ShockleyQueisser (SQ) limit, of about 31% effi ciency under terrestrial conditions. [ 5 ] For a solar cell with 1.13 eV bandgap such as the previous 11.1% champion, [ 2 ] the SQ limits for open circuit voltage ( V oc ) and short-circuit current density ( J sc ) are 820 mV and 43.4 mA cm −2 , respectively. The previous 11.1% champion only achieved a V oc of 460 mV and a J sc of 34.5 mA cm −2 , corresponding to about 56% and 79% of the SQ limit values. In order to boost J sc , an optical architecture with optimized transparent conductive oxide (TCO) and CdS thicknesses has recently been reported, leading to a new CZTSSe record PCE of 12.0% and a J sc that reaches 83% of the SQ limit. [ 1 ] Despite improvements in shortcircuit current, the V oc defi cit, equal to the difference between the bandgap and V oc , is currently the biggest hurdle preventing CZTSSe devices from achieving higher effi ciency. [ 6 ] Enhancement of V oc also directly improves device fi ll factor. [ 7 ] Although many factors can infl uence V oc in a solar cell, carrier generation and recombination near the charge-separating junction play a dominant role. Thus, in order to decrease the V oc defi cit and increase effi ciency beyond 12%, it is critical to understand junction characteristics, current collection, and recombination mechanisms in the current generation of devices.Here, an independently certifi ed world-record 12.6% PCE CZTSSe thin-fi lm solar cell is presented. The new champion device was fabricated using a recently described hydrazine pure-solution approach, targeting a Cu-poor and Zn-rich condition. [ 8 ] Secondary ion mass spectrometry (SIMS) shows that the obtained CZTSSe fi lms exhibit very low carbon and oxygen concentrations, comparable to fi lms fabricated by the more traditional hydrazine-slurry method. [ 9 ] The rheological properties of the particle-free solution, relative to the slurry process, signifi cantly improves the coating uniformity and fi lm structure and, consequently, the performance of the solar cells. [ 4,8 ] By simultaneously optimizing the TCO and CdS thicknesses to maximize photon transmission to the absorber and improving the bulk qualities of CZTSSe with the hydrazine pure-solution approach, both J sc and V oc are boosted in the 12.6% champion device. Device characteristics of the new champion cell, as deduced from current-voltage, quantum effi ciency, capacitance, and electron-beam-induced current (EBI...

High absorption coefficients of the CuSb(Se,Te)2 and CuBi(S,Se)2 alloys enable high-efficient 100 nm thin-film photovoltaics

“…Since the topmost VBs are flat, also the DOS near the valence-band edges are strong if one compare with the DOS of CIGS and CZTSSe. Thus, the CuSb(Se,Te) 2 and CuBi(S,Se) 2 compounds have flat CBs and VBs, and that is an advantage for a strong onset of the optical absorption.…”

“…CZTSSe has not only earth-abundant and low-cost elements but, similar to CIGS, also tunable band-gap energy and large absorption coefficient. The maximum efficiency for CZTSSe based solar cell is today 12.6% by the IBM in New York [2]. However, the device efficiency together with the material usage and manufacturing costs of CIGS and CZTSSe technologies must be considered.…”

Optical properties and surface characterization of pulsed laser-deposited Cu 2 ZnSnS 4 by spectroscopic ellipsometry

“…Unlike CIGS-and CdTebased solar cells, which have surpassed 20% power-conversion efficiencies on the laboratory scale, the current records for CZTS are 8.4% in the case of a sulfur-pure material [1] and 12.6% if S is alloyed with Se [2]. In order to improve the efficiency, both technological issues and a still incomplete understanding of the material need to be addressed.…”

Extended antisite defects in tetrahedrally bonded semiconductors

“…A technologically important example is CZTS which has attracted high interest as a solar absorber material 32,33 . The formation of Cu Sn anti-site point defect in this material leads to the creation of four unfavorable S-Cu 3 Zn motifs, which violate the octet rule by 0.75 electrons.…”