Short Minority Carrier Lifetime Research Articles

Measuring the Electronic Bandgap of Carbon Nanotube Networks in Non-Ideal p-n Diodes.

The measurement of the electronic bandgap and exciton binding energy in quasi-one-dimensional materials such as carbon nanotubes is challenging due to many-body effects and strong electron-electron interactions. Unlike bulk semiconductors, where the electronic bandgap is well known, the optical resonance in low-dimensional semiconductors is dominated by excitons, making their electronic bandgap more difficult to measure. In this work, we measure the electronic bandgap of networks of polymer-wrapped semiconducting single-walled carbon nanotubes (s-SWCNTs) using non-ideal p-n diodes. We show that our s-SWCNT networks have a short minority carrier lifetime due to the presence of interface trap states, making the diodes non-ideal. We use the generation and recombination leakage currents from these non-ideal diodes to measure the electronic bandgap and excitonic levels of different polymer-wrapped s-SWCNTs with varying diameters: arc discharge (~1.55 nm), (7,5) (0.83 nm), and (6,5) (0.76 nm). Our values are consistent with theoretical predictions, providing insight into the fundamental properties of networks of s-SWCNTs. The techniques outlined here demonstrate a robust strategy that can be applied to measuring the electronic bandgaps and exciton binding energies of a broad variety of nanoscale and quantum-confined semiconductors, including the most modern nanoscale transistors that rely on nanowire geometries.

Effect of crystal growth conditions on carrier lifetime and lattice defects in the solar absorber material ZnSnP2

We investigated the minority carrier lifetime and behavior of lattice defects in ZnSnP2 bulk crystals through experiments on carrier recombination and defect properties. Advanced deep level transient spectroscopy (DLTS) revealed that an electron trap with a short time constant at 0.2 eV below the conduction band minimum edge may contribute to the short minority carrier lifetime evaluated by time-resolved photoluminescence (TRPL). The temperature dependence of steady-state photoluminescence suggested that the carrier recombination through the electron trap was nonradiative around room temperature, which supports the fact of the short carrier lifetime and lower current density in ZnSnP2 solar cells. Previously reported theoretical calculation suggests that such a trap comes from the antisite defect of Sn from the viewpoint of the thermodynamic transition level. We, thus, prepared ZnSnP2 crystals by the solution growth method under conditions with a higher chemical potential of Zn, and we achieved the enhancement of the carrier lifetime compared to that under other growth conditions. In this case, the evaluation of the liquidus temperature and chemical potentials by a thermodynamic model indicated that the formation of Sn antisite was effectively suppressed by a lower precipitation temperature in addition to the effect of chemical potentials. Finally, we demonstrated the improvement of current density in ZnSnP2 solar cells using crystals with a longer lifetime, especially in the longer wavelength range.

Bandgap Fluctuations, Hot Carriers, and Band‐to‐Acceptor Recombination in Cu2ZnSn(S,Se)4 Microcrystals

Temperature and laser power dependencies of the band‐to‐acceptor recombination in Cu2ZnSn(S x Se1−x )4 (x = 0.7) microcrystals, which exhibit large bandgap energy fluctuations, are studied. The average depth of these fluctuations is approximately 79 meV. The shape of the corresponding wide photoluminescence (PL) band is analyzed using a modified localized‐state ensemble model. The temperature dependence of this PL band is demonstrated to be influenced by the redistribution of holes between potential wells in the valence band with varying depths. The shape of this band at different temperatures is well fitted when an effective carrier temperature is introduced. This temperature is found to be approximately 300 K higher than the lattice temperature in the samples, and it is mainly caused by the very short minority carrier lifetime. According to the laser power‐dependent PL studies, there is a consistent reduction in the effective carrier temperature as the laser power increases. This phenomenon is explained by the dominance of nonradiative Shockley–Read–Hall recombination at lower temperatures.

Efficient GaAs nanowire solar cells with carrier selective contacts: FDTD and device analysis

Nanowire (NW) solar cells (SCs) with III-V materials have demonstrated superior light harvesting and anti-reflection characteristics, while also consuming less material than planar SCs. However, the performance of NW-based SCs in actual applications falls short of expectations because to their high surface-to-volume ratio and short minority carrier lifetimes. To tackle this, core-shell radial junction SCs are proposed. However, it is extremely difficult to achieve precise doping in both core and shell of NWs while preserving defect-free interface characteristics in the experimental realization, resulting in poor p-n junction quality and significant recombination processes. In this article, we have proposed a core-shell heterojunction SCs composed of p-type GaAs NW as the core material and ITO/TiO2 as the shell material to achieve high efficiency. Using the finite-difference time-domain (FDTD) methodology, we have shown that a coating of ITO/TiO2 shell over a geometrically optimized GaAs core may considerably reduce the cell's optical losses. In addition, using Lumerical's Charge solver module we found that the use of n-type TiO2 coating as an electron-selective can significantly improve the minority carrier transport and collection in the device. The optimized structure has exhibited an efficiency of 18.43% even for low minority carrier life-time (τn) of 100ps and carrier mobility (μn) of 1000cm2V−1s−1 while maintaining high surface recombination velocity (SRV) of 107 cm/s and 104 cm/s at contacts and TiO2/GaAs interface, respectively.

Efficiency enhancement of CZTSe solar cell using CdS(n)/(AgxCu1–x)2ZnSnSe4 (p) /Cu2ZnSnSe4 (p+) structure

Direct bandgap Cu2ZnSnSe4 (CZTSe) material is a promising absorber for thin film photovoltaics due to its affordable production cost and ecofriendly constituents. However, bulk defects, small grain size, short minority carrier lifetime and band bending at CZTSe/Mo (back contact) interface limit the performance of CZTSe solar cells. To overcome these issues, we design a single junction CdS(n)/ (AgxCu1–x)2ZnSnSe4 (p) /Cu2ZnSnSe4 (p + ) solar cell where we use (AgxCu1–x)2ZnSnSe4 (ACZTSe) as the main absorber layer. We have chosen the carrier density of each layer in a such way that ACZTSe becomes depleted and generated minority are collected efficiently. In our design, we utilize CZTSe as the back surface field layer to prevent surface recombination and indium doped tin oxide (ITO) as the back electrode to avoid band bending and increase the open circuit voltage. Additionally, we optimize the thicknesses of different layers and achieve a maximum efficiency of 18.63% including Shockley-Read-Hall, radiative and surface recombination mechanisms. The photo conversion efficiency (PCE) of our designed solar cell is 6% higher (12.6% vs 18.63%) than that of the best reported selenium rich CZTSe solar cell. The design concept proposed in this work would help in harvesting solar energy efficiently from next generation CZTSe solar cells.

Defect Engineering in Earth‐Abundant Cu2ZnSn(S,Se)4 Photovoltaic Materials via Ga3+‐Doping for over 12% Efficient Solar Cells

AbstractThe efficiency of earth‐abundant Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is considerably lower than the Shockley–Queisser limit. One of the main reasons for this is the presence of deleterious cation disordering caused by SnZn antisite and 2CuZn+SnZn defect clusters, resulting in a short minority carrier lifetime and significant band tailing, leading to a large open‐circuit voltage deficit, and hence, low efficiency. In this study, Ga‐doping is used to increase the CZTSSe solar cell efficiency to as high as 12.3%, one of the highest for this type of cells. First‐principles calculations show that the preference of Ga3+ occupying Zn and Sn sites has a benign effect on suppressing the formation of the SnZn deep donor defects by upwardly shifting the Fermi level, which is further confirmed by deep‐level transient spectroscopy characterization. Besides, the Ga dopants can also form defect‐dopant clusters, such as GaZn+CuZn and GaZn+GaSn, which also have positive effects on suppressing the band‐tailing states. The defect engineering via Ga3+‐doping may suppress the band‐tailing defect with a decreased Urbach energy, elevate the minority carrier lifetime, and in the end, enhance the VOC from 473 to 515 mV. These results provide a new route to further increase CZTSSe‐based solar cell efficiency by defect engineering.

Progress of long wavelength infrared focal plane arrays based on antimonide compounds superlattice

<p indent=0mm>The research of antimonide compounds began with 1950s. With the appearing of superlattice concept and energy band engineering in the 1970s, the potentials in infrared detection of antimonide compounds gradually emerged. Due to the reality demand, epitaxy and preparation technologies of antimonide-based materials have achieved rapid progress. The rapid advance of T2SL also benefits from the previously five decades ago of development of III-V group materials and devices research. The development of InAs/GaSb type-II superlattices (T2SLs) results from two primary motivations: the InAs/GaSb superlattice has more apparent advantages than HgCdTe in low cost, reproducibility, operability and high uniformity, especially for long wavelength detector. Secondly, the Auger recombination probability of type II superlattices is lower than that of HgCdTe, which means that the infrared detector of type II superlattice has a lower dark current or a higher working temperature than that of HgCdTe detector. And improving the working temperature of the long-wave focal plane is crucial for reducing the power consumption, size and weight of the imaging system. In addition, the atmosphere window with highest transmittance is located at the range of <sc>8−14 μm.</sc> And the emitted infrared radiation by an object at room temperature <sc>(300 K)</sc> has a wavelength of about <sc>10 μm.</sc> Therefore, long wavelength infrared detection is extremely valuable for InAs/GaSb type-II superlattices. Compared with HgCdTe device, T2SL detectors can provide equivalent or better performance under the same cutoff wavelength. But the short minority carrier lifetime of InAs/GaSb superlattice cause a high level of generation-recombination current (<italic>J</italic>_gr). In order to suppress <italic>J</italic>_gr and other dark current, the different device structures like W-structure, PπMN structure, CBIRD and unipolar barrier were put forward and employed in the detectors. As a result, the dark current and impedance was greatly improved. Furthermore, with the putting forward of InAs/InAsSb superlattice, the defects level in band gap introduced by Ga were avoided, and the minority carriers lifetime were effectively improved. The reproducibility, operability and uniformity of T2SL bring more advantages than HgCdTe detector with the sustainable developement of T2SL technologies and theories.

Carrier lifetime control by intentional boron doping in aluminum doped p-type 4H-SiC epilayers

The carrier lifetime control in p-type 4H-SiC epilayers with intentional aluminum (Al) and boron (B) doping is demonstrated as part of work to develop a p-type “recombination-enhancing layer” for n-channel insulated gate bipolar devices fabricated on p-type substrates. The (Al + B)-doped epilayers (Al: 5 × 1017, B: 4 × 1016 cm−3) showed a very short minority carrier lifetime of less than 20 ns at 293 K, resembling that of highly Al-doped epilayers (Al: 1 × 1019 cm−3). Besides, the minority carrier lifetimes in (Al + B)-doped epilayers are stable against post-annealing in Ar and H2 ambient, while that of Al-doped epilayers varied considerably. PiN diodes with a 10 μm-thick (Al + B)-doped buffer layer inserted on p-type substrates showed no evident degradation after a stress test under a pulse current density of 2000 A/cm2.

Growth and Characterization of Arsenic-Doped CdTe1−xSex Single Crystals Grown by the Cd-Solvent Traveling Heater Method

The photovoltaic performance of CdTe solar cells is mainly limited by low doping and short minority carrier lifetime. Group-V element doping and Se-alloying have a significant impact on tuning these fundamental CdTe properties. In this paper, we report the growth of p-type As-doped, Cd-rich CdTe1−xSex single crystals using metallic Cd as the solvent in the traveling-heater method. The structural and electrical properties of CdTe1−xSex are examined for different Se concentrations. CdTe1−xSex single crystals (0 ≤ x ≤ 0.5) with zincblende structure indicate homogeneous composition. The 1017 cm−3 As-doping activation efficiency can be maintained at close to 50% for x ≤ 0.2. Se alloying leads to bulk minority carrier lifetime exceeding 30 ns for samples doped near 1017 cm−3. These results help us to overcome the current roadblocks in device performance.

InSb pixel loaded microwave resonator for high-speed mid-wave infrared detection

High-speed mid-wave infrared (MWIR) detectors are of significant interest for a wide range of applications in communication and spectroscopy. High-speed photodetection is conventionally achieved using reverse biased semiconductor p-i-n junction devices. However, implementing such structures in the mid-infrared (mid-IR) is challenging due to both the limited available material platforms and challenges associated with device design. Here we demonstrate a high-speed MWIR detector architecture that uses a microwave resonator circuit loaded with a photoconductive indium antimonide (InSb) pixel, originally grown highly lattice-mismatched on a GaAs substrate. Time domain measurements demonstrate sub-nanosecond detector response at temperatures from 77 K to room temperature. Frequency response measurements demonstrate that optical signals modulated at frequencies as high as 2 GHz can be well resolved up to room temperature. Time domain circuit simulations support the experimentally measured short minority carrier lifetimes in the InSb pixel, while also suggesting a circuit time constant of ~200 ps, which is ultimately the limiting factor for the bandwidth of the presented detector architecture. Our results provide an alternative approach for the development of contact-free, high-speed infrared detectors capable of directly interfacing with microwave components and structures for a range of RF/mid-IR applications.

Minority carrier lifetime of Ge film epitaxial grown on a large-grain seed layer on glass

To develop high-efficiency multijunction solar cells onto inexpensive substrates, an innovative technique for growing a large-grained Ge layer on glass is strongly desired. We investigated the epitaxial growth of a light absorbing Ge film (500-nm thickness) on a large-grained (>100 μm) Ge seed layer (50-nm thickness) formed on glass by Al-induced layer exchange. After examining molecular beam epitaxy (MBE) and solid-phase epitaxy (SPE) for both methods, Ge layers with a low Al concentration were epitaxial grown at 350 °C. Microwave photoconductivity decay revealed that the MBE-Ge layer exhibited a short minority carrier lifetime owing to the rough surface. Conversely, the SPE-Ge layer was relatively flat and exhibited a long bulk minority carrier lifetime (5.6 μs), which is close to that of a single-crystal Ge. Therefore, the seed layer concept that combines SPE with Al-induced layer exchange is a promising way for fabricating ideal bottom cells for high-efficiency multijunction solar cells based on inexpensive substrates.

Dielectric-induced interface states in black phosphorus and tungsten diselenide capacitors

The interfaces between two-dimensional (2D) materials and gate dielectrics play an important role in the performance and reliability of 2D electronic devices. In this work, we systematically studied the capacitance and interface states of a narrow bandgap material (black phosphorus, BP) and an intermediate bandgap material (tungsten diselenide, WSe2). We found that their capacitance–voltage (CV) characteristics are drastically different. The BP capacitor CVs demonstrate ambipolar and low-frequency properties, while WSe2 capacitor CVs shows unipolar (p-type) and high-frequency behavior. The narrow bandgap of BP (∼0.3 eV) enables large amounts of minority carriers, low generation-recombination resistance, and short minority carrier lifetime, giving low-frequency behavior of the CVs, while the wide bandgap of WSe2 (∼1.21 eV) leads to the high-frequency behavior of the CVs. The nearly intrinsic (low) doping of the BP flake results in ambipolar CVs which are symmetric about the midgap. The naturally p-type doping in WSe2 gives unipolar CVs similar to p-type silicon. In both materials, the interface state density is as high as 1013 cm−2 eV−1. Although 2D materials are free of dangling bonds, their intimate contact with high-k dielectrics like Al2O3 could generate a larger number of interface states and degrades the device performance. Hexagonal boron nitride (hBN) effectively reduces the interface state density as dielectrics. The interface state for BP/hBN capacitor shows much lower density than counterpart with Al2O3 gate dielectric. We also found that the interface state density increases exponentially with the gate voltage when the surface Fermi level is swept from the midgap toward the band edge.

Electron and Proton Irradiation Damage in β-Ga2O3 Vertical Rectifiers

Wide bandgap semiconductors materials have always been the interest of their ability that can withstand high radiation fluences for the military, nuclear-industry monitoring, satellites and other space-borne applications. Monoclinic β phase Ga2O3 is attracting great attention for power electronics and solar-blind photodetectors because of its large bandgap (~4.9 eV) and a critical electric field strength of 8 MV/cm.[1,2,3] Also, the large diameter bulk β- Ga2O3 is commercially available with a controllable n-type doping for its epitaxial layers. Given its high bond strength and expected high vacancy formation energy, β- Ga2O3 is likely to be very radiation hard based on the reduced density of atomic displacements expected for a given energy of non-ionizing radiation exposure.[4] The cosmic rays, trapped radiation in the Earth’s radiation belts, and solar particle events are three primary sources of space irradiation. The cosmic rays consist predominantly of protons; the radiation belts contain energetic protons and electrons while solar particle events are mostly lower energy protons and electrons, in which the average integral proton fluxes at 10 MeV are of order 1014 cm-2.[1] Thus, it is important to understand the effect of energetic proton irradiation on Ga2O3. For electron irradiation, vertical rectifiers fabricated on epi Ga2O3 (Si-doped, 10 μm) on bulk (001) β- Ga2O3 substrate (Sn-doped, 650 μm) with Ti/Au as the ohmic contact for the full back area and Ni/Au for Schottky contacts in the front. The rectifiers were subject to 1.5 MeV electron irradiation at fluences from 1.79 × 1015 to 1.43 × 1016 cm-2 at a fixed beam current of 10-3 A. The electron irradiation caused a reduction in carrier concentration in the epi Ga2O3, with a carrier removal rate of 4.9 cm-1. The electron-induced damage would cause the 2kT region of the forward current-voltage characteristics increase. For the highest electron fluence, the diode ideality factor increased around 8% along with two orders of magnitude increase in on-state resistance. There was a significant reduction in reverse bias current that scaled with electron fluence. The diode on/off ratio was measured when switching from +1 V to -40 V. At -10 V reverse bias voltage, the on/off ratio was severely degraded by electron irradiation, decreasing from ~107 in the reference diodes to ~2 × 103 for the 1.43 × 1016 cm-2 fluence. The reverse recovery characteristics showed little changes even at the highest fluence, with the reverse recovery time in the range 21-25 nsec for all rectifiers. This phenomenon can be explained by the short minority carrier lifetime. which controls the carrier storage time in Ga2O3 intrinsic layer.[3] Also, based on the diode on/off ratio, the primary cause of the degradation was introduced by the reduction of majority carrier concentration. Regarding proton irradiation, β- Ga2O3 vertical rectifiers were subject to 10 MeV proton irradiation at a fixed fluence of 1014 cm-2. The electrical performance of vertical rectifiers was measured before and after proton irradiation, as well as subsequent annealing up to 450°C. The carrier removal rate was determined to be 235.7 cm-1, which is comparable to the carrier removal rate for GaN-based heterostructures under the same proton energy. Point defects introduced by the proton damage create trap states that reduce the carrier concentration in the Ga2O3. Even annealing at 300°C produces a recovery of approximately half of the carriers in the Ga2O3, while annealing at 450°C almost restores the reverse breakdown voltage. The diode on/off ratio of the rectifiers switched from +1 V to -40 V. The diode on/off ratio was severely degraded by proton irradiation and this was only partially recovered by 450°C annealing. The minority carrier diffusion length decreased from ~340 nm for the reference diode to ~315 nm after the proton irradiation. R. Benton and E. V. Benton, Nucl. Instr. and Meth. in Phys. Res. B 184, 255 (2001).Higashiwaki, K. Sasaki, H. Murakami, Y. Kumagai, A. Koukitu, A. Kuramata, T. Masui and S. Yamakosh, Semicond. Sci. Technol., 31, 034001 (2016).Higashiwaki, K. Sasaki, A. Kuramata, T. Masui and S. Yamakoshi, Appl. Phys. Lett., 100, 013504 (2012).I. Stepanov, V.I. Nikolaev, V. E. Bougrov and A.E. Romanov, Rev. Adv. Mater. Sci., 44, 63 (2016). Figure 1

Minority lifetime and efficiency improvement for CZTS solar cells via Cd ion soaking and post treatment

Short minority carrier lifetime and low open circuit voltage (Voc) are key issues limiting the current efficiency development for Cu2ZnSnS4 (CZTS) thin film solar cells. This work presents the use of Cd ion soaking and post-heat treatment to increase the lifetime and Voc of CZTS. The time-resolved photoluminescence (TRPL) results confirmed that Cd ion soaking and post heat treatment is effective in enhancing the minority lifetime, from ∼10 ns up to ∼28 ns. With analyses of the current density- voltage (J-V) curves and external quantum efficiency (EQE) data, Cd ion soaking and subsequent post heat treatment is found to greatly reduce the recombination and improve the junction quality, contributing to a ∼70 mV Voc enhancement and resulting in the increased device efficiency of 7.6%, from 5.9%.

V and Ti Doping in 4H-SiC Epitaxy for Reduction of Carrier Lifetimes

Epitaxial growth of 4H-SiC with intentional V or Ti doping was performed to obtain short minority carrier lifetimes, using VCl4 or TiCl4 as the doping sources. The doping efficiencies and quality of the epilayers were compared for H2+SiH4+C3H8 and H2+SiH4+C3H8+HCl gas systems. The addition of V or Ti in highly N-doped epilayer demonstrated very short minority carrier lifetimes of 20-30 ns at 250°C.

Suppression of the Forward Degradation in 4H-SiC PiN Diodes by Employing a Recombination-Enhanced Buffer Layer

Application of highly N-doped buffer layers or a (N+B)-doped buffer layer to PiN diodes to suppress the expansion of Shockley stacking faults (SSFs) from the epilayer/substrate interface was studied. These buffer layers showed very short minority carrier lifetimes of 30–200 ns at 250°C. The PiN diodes were fabricated with buffer layers of various thicknesses and were then tested under high current injection conditions of 600A/cm2. The thicker buffer layers with shorter minority carrier lifetimes demonstrated the suppression of SSFs expansion and thus that of diode degradation.

Analysis of loss mechanisms in Ag2ZnSnSe4 Schottky barrier photovoltaics

Recently, a new type of photovoltaic device based on an n-type Ag2ZnSnSe4 (AZTSe) absorber was demonstrated with an efficiency of over 5%. This work examines in detail several critical loss mechanisms in FTO/AZTSe/MoO3/ITO Schottky barrier devices. It is shown that the Schottky barrier height in the present devices under illumination is only ∼0.82 eV. With a barrier height of this magnitude, the device has an upper-bound of only 6.4% to the efficiency. Second, the AZTSe thin films used in the present devices exhibit exceptionally short minority carrier lifetimes (≤225 ps), as probed using two-photon spectroscopy. Third, hysteresis is observed in the J–V response of these devices. Pulsed electrical measurements reveal that reverse-bias voltage pulses create residual shunts in the device proportional to the pulse amplitude and duration. Reversible Ag-doping of the MoO3 buffer is proposed as an explanation of the observed shunting upon reverse bias. Therefore, improving the contact materials and the minority carrier lifetime is identified to be critically important for improving AZTSe-based photovoltaics. Finally, AZTSe is found to be photo-conductive with a Hall carrier density that increases by two orders of magnitude upon illumination. The origin of this effect is still unknown.

Short minority carrier lifetimes in highly nitrogen-doped 4H-SiC epilayers for suppression of the stacking fault formation in PiN diodes

We investigated the dependency of minority carrier lifetimes on the nitrogen concentration, temperature, and the injected carrier concentration for highly nitrogen-doped 4H-SiC epilayers. The minority carrier lifetimes greatly shortened when the nitrogen concentration exceeded 1018 cm−3 through enhancing direct band-to-band and Auger recombination and showed a slight variation in the temperature range from room temperature (RT) to 250 °C. The epilayer with a nitrogen concentration of 9.3 × 1018 cm−3 exhibited a very short minority carrier lifetime of 38 ns at RT and 43 ns at 250 °C. The short minority carrier lifetimes of the highly nitrogen-doped epilayer were confirmed to maintain the values even after the subsequent annealing of 1700 °C. 4H-SiC PiN diodes were fabricated by depositing a highly nitrogen-doped epilayer as a “recombination enhancing layer” between an n− drift layer free from basal plane dislocations and the substrate. The PiN diodes showed no formation of stacking faults and no increase in forward voltage during current conduction of 600 A/cm2 (DC), demonstrating that a highly nitrogen-doped buffer layer with a short minority carrier lifetime successfully suppresses the “bipolar degradation” phenomenon.

Core-shell structured Si/ZnO photovoltaics

Periodic Si pillar arrays synthesized by metal assisted chemical etching method exhibit an excellent light harvesting capability, ideal for core-shell structured solar cell applications. To investigate the photovoltaic prospective, a radial heterojunction device is fabricated by conformal coating a layer of Al doped ZnO film on the p-Si pillar array. This core-shell structure has achieved low reflectance (<12%) over a broad wavelength range, and has demonstrated more than doubled enhancement of the short-circuit current as compared to the traditional planar architecture. Although reverse recovery transient measurement shows that this device with no surface passivation has shorter minority carrier life time than the planar structure, the overall efficiency is enhanced. It suggests that device efficiency could be much improved through proper surface treatment. This renders a promising path for core-shell structured solar cell with higher efficiency yet reduced material per device element.

Indications of short minority-carrier lifetime in kesterite solar cells

Solar cells based on kesterite absorbers consistently show lower voltages than those based on chalcopyrites with the same bandgap. We use three different experimental methods and associated data analysis to determine minority-carrier lifetime in a 9.4%-efficient Cu2ZnSnSe4 device. The methods are cross-sectional electron-beam induced current, quantum efficiency, and time-resolved photoluminescence. These methods independently indicate minority-carrier lifetimes of a few nanoseconds. A comparison of current-voltage measurements and device modeling suggests that these short minority-carrier lifetimes cause a significant limitation on the voltage produced by the device. The comparison also implies that low minority-carrier lifetime alone does not account for all voltage loss in these devices.