Emitter Doping Research Articles

Selective Boron Emitters Using Laser-Induced Forward Transfer Versus Laser Doping From Borosilicate Glass

Although highly doped boron selective emitters (SEs) can be formed by using laser doping (LD) from the borosilicate glass remaining after boron tribromide tube diffusion, the dopant concentration is limited. This limitation can be overcome by using a laser-induced forward transfer (DLIFT) approach. In this work, SEs formed by DLIFT and LD are compared to a homogenous tube diffusion (Diff) emitter. We investigated the correlation of the emitter saturation current density ( j 0 e ) and the specific contact resistance $(\rho _{c})$ with the sheet resistance $(R_{{\rm{sheet}}})$ and the laser pulse energy density $(E_{p,d})$ . For passivated emitters, $j_{{0}e}$ of DLIFT and LD emitters was around ten times higher than $j_{{0}e}$ of Diff emitters. For metallized emitters, simulated $j_{{0}e}$ of DLIFT emitters was lower than $j_{{0}e}$ of LD and Diff emitters for $R_{{\rm{sheet}}}\,{\rm{ glt; \,40.0\,\Omega / sq}}$ . Moreover, we show how $j_{{0}e}$ can be further reduced by increasing the surface dopant concentration of the boron emitter and by reducing the laser-induced defects in the silicon crystal. Additionally, the metallization of DLIFT emitters with aluminum–silver paste by screen printing provided low contact resistances between metal and silicon ( ρc < 1.0 mΩ · cm2). Thus, p-type emitters can be optimized by forming an SE with the highly doped boron regions achieved by DLIFT under the screen-printed metallization.

Challenges for lowly-doped phosphorus emitters in silicon solar cells with screen-printed silver contacts

This work points out that the application of phosphorus emitters with low surface concentration Nsurf of a few 1019 cm-3 in combination with state-of-the-art screen-printed and fired silver contacts is no more limited by the specific contact resistance ρC but by the dark saturation current densities underneath the metal contacts j0,met. Eight emitter doping profiles have been designed with different Nsurf ranging between 3.3·1019 cm-3 and 1.2·1020 cm-3 which feature very similar junction depths of about 350 nm. The measured ρC values for these emitters are determined to be between 2 mΩcm2 and 5 mΩcm2 for about 50 µm-wide contact fingers. Their emitter dark saturation current density (alkaline textured and passivated surface) range from 40 fA/cm² to 90 fA/cm². From these parameters and the current-voltage data of large-area Czochralski-grown silicon solar cells featuring an aluminum back surface field, we estimate j0,met to be between 1200 fA/cm² and 3900 fA/cm². Our results show that for decreasing Nsurf, the recombination underneath the metal contacts increases significantly which mainly limits the cell’s open-circuit voltage. We thus conclude that the major challenge for emitters with low Nsurf consists in achieving reasonable low j0,met values in order to benefit on the cell level from the lower recombination activity in the passivated, non-metallized surface area.

1.0 eV GaAs based InAs quantum dot solar cells

There are great improvements in III-V semiconductor solar cells including GaAs single junction solar cell and tandem solar cells in last decades. The common commercially used triple-junction solar cell mostly utilize a Ge bottom cell with an (In)GaAs and InGaP middle and top cell respectively. The (In)GaAs middle cell absorbs limited solar spectrum and show minimum short-circuit current in multiple junction solar cell, which determine the overall current of the cell. Theoretically, higher energy conversion efficiency will be obtained when introducea subcell with 1.0 eV band gap in series to the InGaP/GaAs/Ge tandem structures. Lattice-matched GaInNAs and lattice-mismatched In0.3Ga0.7As are two common choices for achieving 1.0 eV band gap. However, the addition of N to GaAs has detrimental effects on the material quality, limiting its utility to approaches that required photocurrent. And the lattice mismatch makes thick In0.3Ga0.7As heterogeneous epitaxial difficult. The incorporation of low band gap nanoscale materials, such as quantum well and quantum dots, into current limiting junction of a multijunction solar cell can tuning the effective bandgap and enhance the low-energy photon absorption, thereby increasing the short-circuit current. The samples are grown by solid-source molecular beam epitaxy (V80H) on p-GaAs (001) substrates using an As4 source. Sample A is a standard GaAs solar cell with PIN structure. Sample B contains 10 period 8 nm In0.15Ga0.85As QW and sample C contains 10 period InAs dots-in-well structure. The intrinsic region of these samples was at the same length of 630 nm to obtain the same build-in electric field. Besides the instinct region, the three samples are designed the same. The ohmic contact layer’s doping concentration is N D/ N A=3×1018 cm−3 and its thickness is 300 nm. The emitter doping concentration is N D=5×1017 cm−3 and its thickness is 150 nm; The base doping concentration is N A=5×1017 cm−3 and its thickness is 300 nm. The As4 pressure and the InAs QDs growth rate are 1×10−5 Torr and 0.1 ML/s, respectively. The XRD pattern of sample B (QWSC) shows clearly defined and intense satellite peaks indicating steep interface and periodicity quantum well. However, the XRD pattern of sample C (the InAs dots in well solar cell) shows blurring diffraction peaks which means increased interface roughness. Uniform QD structure with density of 2×1010 cm−2 can be observed in SEM. From the STEM, we can see well-defined unrelated pyramidal quantum dots separated by a nominal 50 nm GaAs spacing. From the contrast, the pyramid InAs QDs are estimated to have the lateral dimension of 27 nm and the height of 12 nm. The PC response of sample A rise at 600 nm and fall off at 870 nm, which is corresponding to the GaAs bandgap according to the PL peak position; the PC response of QWSC (sample B) rise at 600 nm and fall off at 990 nm, which is corresponding to the In0.15Ga0.85As bandgap in PL spectrum. The incorporation of In0.15Ga0.85As quantum wells in GaAs standard solar extend the absorption of solar spectrum from 900 nm to 1000 nm. The wavelength region from 700 nm to 900 nm in PC of QWSC is weaker than the GaAs standard solar cell. The insertion of InAs QDs into QWSC can extend the infrared photon absorption to the wavelength of 1300 nm. The insertion of InAs quantum dots into In0.15Ga0.85As/GaAs quantum well solar cell extend the absorption of infrared light and the J sc reaches 13.68 mA/cm2, giving a 37.8% increase in short-circuit current over the baseline solar cell current. Because the voltage of multiple junction solar cell is the sum of the sub cell’s voltage. The voltage decreasement with the insertion of InAs quantum dots do not influence the overall voltage of multiple junction solar cell. In summary, the incorporation of quantum well and quantum dots in GaAs solar cell result in extended solar spectrum absorption and contribute to the sub-band gap current gains for GaAs solar cell. Especially, InAs dots-in-well solar cell can extend the absorption spectrum to the wavelength of 1300 nm, and increase by 37.8% in short-circuit current, which shows great potential in mitigating current mismatch of multiple junction solar cell. Furthermore, designing new multiple junction solar cell becomes possible.

Lifetime Analysis for Comparing POCl3 Diffused Emitter Doping Characteristics in p-Type Silicon Solar Cells Using QSSPC

Analysis of the emitter property of solar cells is important because the emitter doping characteristics can affect the surface recombination velocity, contact resistance, emitter saturation current density, and cell efficiency. To analyze the emitter quality, we used the following methods: the four-point probe method, quasi-steady-state photoconductance (QSSPC), and secondary ion mass spectroscopy (SIMS). The four-point probe method is used to measure the doping dose in the emitter. Using QSSPC, we can characterize the emitter quality, including the lifetime of the emitter, and using SIMS, we can measure the concentration of dopants as a function of depth in the emitter. However, SIMS measurement is destructive and limited to the measurement of planar surface wafers. To solve this problem, we investigated the relationship between the minority carrier lifetime and the emitter doping profile using the QSSPC. The relationship between the lifetime and emitter doping profile showed that the lifetime of the emitter decreases as the emitter doping concentration increases. From this result, we performed a lifetime analysis for differently doped POCl3-diffused emitters. The results obtained using the theoretical model for the lifetime agreed with experimental SIMS measurement results, indicating that the model can be used as a quantitative model for comparing emitter doping characteristics.

Recombination processes in passivated boron-implanted black silicon emitters

In this paper, we study the recombination mechanisms in ion-implanted black silicon (bSi) emitters and discuss their advantages over diffused emitters. In the case of diffusion, the large bSi surface area increases emitter doping and consequently Auger recombination compared to a planar surface. The total doping dose is on the contrary independent of the surface area in implanted emitters, and as a result, we show that ion implantation allows control of emitter doping without compromise in the surface aspect ratio. The possibility to control surface doping via implantation anneal becomes highly advantageous in bSi emitters, where surface passivation becomes critical due to the increased surface area. We extract fundamental surface recombination velocities Sn through numerical simulations and obtain the lowest values at the highest anneal temperatures. With these conditions, an excellent emitter saturation current (J0e) is obtained in implanted bSi emitters, reaching 20 fA/cm2 ± 5 fA/cm2 at a sheet resistance of 170 Ω/sq. Finally, we identify the different regimes of recombination in planar and bSi emitters as a function of implantation anneal temperature. Based on experimental data and numerical simulations, we show that surface recombination can be reduced to a negligible contribution in implanted bSi emitters, which explains the low J0e obtained.

Simultaneous measurement of doping concentration and carrier lifetime in silicon using terahertz time-domain transmission

In this work, we present a measurement approach enabling the simultaneous determination of sheet resistance and carrier lifetime in semiconductor samples. It is based on a classic Terahertz (THz) time-domain transmission spectroscopy scheme extended by quasi-steady state optical excitation. The carrier lifetime is determined by contactless THz probing of the increase in sheet conductance associated with quasi-steady-state excitation. Combining a successive etch-back of the surface with repeated THz measurements yields a depth profile of the doping concentration and the carrier lifetime, which is important for the optimization of the emitter of solar cells, for instance. The viability of our approach is demonstrated by investigating a phosphorous doped emitter of a silicon solar cell with the THz approach and comparing the results with electrochemical capacitance voltage measurements.

Color stable and highly efficient hybrid white organic light-emitting devices using heavily doped thermally activated delayed fluorescence and ultrathin non-doped phosphorescence layers

Blue/orange complementary fluorescence/phosphorescence hybrid white organic light-emitting devices with excellent color stability and high efficiency have been fabricated, which are based on an easily fabricated multiple emissive layer (EML) configuration with an ultrathin non-doped orange phosphorescence EML selectively inserted between heavily doped blue thermally activated delayed fluorescence (TADF) EMLs. Through systematic investigation and improvement on luminance-dependent color shift and efficiency deterioration, a slight Commission Internationale de 1′Eclairage coordinates shift of (0.008, 0.003) at a practical luminance range from 1000 to 10000 cd/m2, a maximum power efficiency of 45.8 lm/W, a maximum external quantum efficiency (EQE) of 15.7% and an EQE above 12% at 1000 cd/m2 have been achieved. The heavily doped blue TADF emitters which act as the main charge transport channels and recombination sites in the host with high-lying lowest triplet excited state, take advantage of the bipolar transport ability to broaden the major charge recombination region, which alleviates triplet energy loss. The selectively inserted ultrathin non-doped orange EML makes its emission mechanism dominated by Förster energy transfer, which is effective to keep color stable under different drive voltages.

Impact of Extended Contact Cofiring on Multicrystalline Silicon Solar Cell Parameters

During the temperature spike of the contact cofiring step in a solar cell process, it has been shown that the concentration of lifetime-killer dissolved metallic impurities increases, while adding an annealing after the spike getters most of the dissolved impurities toward the phosphorus emitter, where they are less detrimental. The contact cofiring temperature profile, including the after-spike annealing, has been called extended contact cofiring, and it has also been proposed as a means to decrease the emitter saturation current density of highly doped emitters, thus benefiting a wide range of materials in terms of detrimental impurity content. The aim of the present work is to determine the effect of performing this additional annealing on contact quality and solar cell performance, looking for an optimal temperature profile for reduction of bulk and emitter recombination without affecting contact quality. It presents the effect of the extended cofiring step on fill factor, series resistance, and contact resistance of solar cells manufactured with different extended cofiring temperature profiles. Fill factor decreases when extended cofiring is performed. Series resistance and contact resistance increase during annealing, and this happens more dramatically when the temperature peak is decreased. Scanning electron microscopic images show silver crystallites in contact with silver bulk before the annealing that allow a direct current path, and silver crystallites totally surrounded by glass layer ( $>$ 100 nm thick) after annealing. Glass layer redistribution and thickening at low temperatures at the semiconductor–metal interface can be related to the series resistance increase. Degradation of series resistance during the temperature spike, when it is below the optimum one, can also be attributed to an incomplete silicon nitride etching and silver crystallite formation. To make full use of the beneficial effects of annealing, screen-printing metallic paste development supporting lower temperatures without a thick glass layer growth is needed.

Small-area Si Photovoltaics for Low-Flux Infrared Energy Harvesting.

Silicon photovoltaics are prospective candidates to power mm-scale implantable devices. These applications require excellent performance for small-area cells under low-flux illumination condition, which is not commonly achieved for silicon cells due to shunt leakage and recombination losses. Small area (1-10 mm2) silicon photovoltaic cells are studied in this work, where performance improvements are demonstrated using a surface n-type doped emitter and Si3N4 passivation. A power conversion efficiency of more than 17% is achieved for 660 nW/mm2 illumination at 850 nm. The silicon cells demonstrate improved power conversion efficiency and reduced degradation under low illumination conditions in comparison to conventional crystalline silicon photovoltaic cells available commercially.

Comparison of Boron diffused emitters from BN, BSoD and H3BO3 dopants

In this work, we are comparing different limited boron dopant sources for the emitter formation in n-type c-Si solar cells. High purity boric acid solution, commercially available boron spin on dopant and boron nitride solid source are used for comparison of emitter doping profiles for the same time and temperature conditions of diffusion. The characterizations done for the similar sheet resistance values for all the dopant sources show different surface morphologies and different device parameters. The measured emitter saturation current densities (Joe) are more than 20 fA cm−2 for all the dopant sources. The bulk carrier lifetimes measured for different diffusion conditions and different solar cell parameters for the similar sheet resistance values show the best result for boric acid diffusion and the least for BN solid source. So, different dopant sources result in different emitter and cell performances.

Si Heterojunction Solar Cells: A Simulation Study of the Design Issues

Silicon heterojunction solar cells having semiconducting oxide-selective contacts can revolutionize the photovoltaic industry with the promise of low cost and high efficiency. In this paper, we have identified the potential design issues of silicon heterojunction cell using simulation. This paper compares two possible electron-selective oxides (TiO2 and ZnO) and two possible hole-selective oxides (CuAlO2 and NiO). The Fermi level in the oxide at the oxide/metal interface is pinned by the metal (its workfunction and eventual interface dipoles). We considered this effect, which determines the effective workfunction of the metal contact as opposed to the actual metal workfunction. Our simulation suggests that Fermi level pinning has significant impact on the device performance. We also considered different interface passivation effects and oxide dopings in our simulation. The simulation suggests that high doping in oxides is beneficial to counter balance the effect of poor surface passivation. This paper provides an extensive understanding of the design of Si heterojunction solar cell using band-engineered semiconducting oxide as the selective contact replacing highly doped emitter and back surface field.

POCl3 diffusion for industrial Si solar cell emitter formation

POCl3 diffusion is currently the de facto standard method for industrial n-type emitter fabrication. In this study, we present the impact of the following processing parameters on emitter formation and electrical performance: deposition gas flow ratio, drive-in temperature and duration, drive-in O2 flow rate, and thermal oxidation temperature. By showing their influence on the emitter doping profile and recombination activity, we provide an overall strategy for improving industrial POCl3 tube diffused emitters.

Emitter doping profiles optimization and correlation with metal contact of multi-crystalline silicon solar cells

A systematic investigation of Phosphorus Oxychloride (POCl3) based diffusion optimization for the formation of homogeneous emitters and correlation with metal contact in p-type multi-crystalline silicon (multi-Si) solar cell is presented. The deposition temperature (810, 804, 798, 792 and 786°C) was varied to achieve different sheet resistance (85, 90, 95, 100, and 105ohm/square) measured by four points probes. The correlation between emitter quality, metal contact resistance (Rc) and cell performance was investigated. The results showed that the sheet resistance is higher, phosphorus surface concentration (Cs) is lower and emitter saturation current density (Joe) is lower. The cell data showed that the higher Rsheet result in higher Voc and Isc due to better short wavelength response from the External Quantum Efficiency (EQE) measurement, but lower fill factor (FF) due to higher emitter sheet resistance and contact resistance with Ag paste. The optimal Rsheet for this type of Ag paste (Samsung SDI 8630A) in this test is 90ohm/square with the highest cell efficiency of 18.325%.

Recombination Behavior of Photolithography-free Back Junction Back Contact Solar Cells with Carrier-selective Polysilicon on Oxide Junctions for Both Polarities

We report on ion-implanted, inkjet patterned back junction back contact silicon solar cells with POLysilicon on Oxide (POLO) junctions for both polarities – n+ doped BSF and p+ doped emitter. The recombination behavior is investigated at two different processing stages: before and after trench separation of p+ and n+ regions within polysilicon (poly-Si). Before trench separation, we find a systematic dependence of the recombination behavior on the BSF index, i.e. the p+n+-junction meander length in the poly-Si. Obviously, recombination at the p+n+-junction in the poly-Si limits the implied open circuit voltage Voc,impl. at one sun illumination and the implied pseudo fill factor pFFimpl. to 695 mV and 80%, respectively. After trench isolation, however, Voc,impl (pFFimpl.) values increase up to 730 mV (85.5%), corresponding to a pseudo-efficiency of 26.2% for an assumed short circuit current density Jsc of 42 mA/cm2. We demonstrate a photolithography-free back junction back contacted solar cell with p-type and n-type POLO junctions with an in-house measured champion efficiency of 23.9% on a designated area of 3.97 cm2. This efficiency is mainly limited by the imperfect passivation in the undoped trench regions and at the undoped front side.

PC1Dmod 6.2 – Improved Simulation of c-Si Devices with Updates on Device Physics and User Interface

In this paper we present a new update to PC1Dmod, which extends the original PC1D program by implementing Fermi-Dirac statistics and a range of state-of-the-art models in order to improve the accuracy of c-Si device simulation. In PC1Dmod 6.2 the list of models is further expanded to include a parameterization of incomplete ionization of dopants (Altermatt et al., J. Appl. Phys.100, 113715, 2006), with parameters for phosphorus, boron, arsenic, gallium and aluminum. The results have been verified against a previous implementation of the model. We show that the inclusion of incomplete ionization is of particular importance for moderately doped surface regions with doping densities in the range ∼5 × 1017 to ∼5×1019 cm-3, resulting in a deviation of up to 15% in the simulated recombination current density and sheet resistance. The effect of incomplete ionization is also shown to be more pronounced in devices made from compensated Si material. Furthermore, the default solar spectrum has also been updated in PC1Dmod 6.2, taking advantage of the increased maximum file size to include a more realistic representation. The generation profiles calculated using PC1Dmod 6.2 together with input from OPAL 2 agree well with results from Sentaurus TCAD for both planar and pyramidally textured surfaces, thus facilitating a more direct comparison between PC1Dmod 6.2 and other simulation programs utilizing standard spectra. The simulation comparison is also extended to the electrical performance of the modeled devices, showing good agreement in the calculated short-circuit current density for a range of planar and textured solar cells with varying emitter doping. Finally, several new output options, including emitter saturation current and injection-dependent lifetime curves have been added, enabling a simpler and more direct way for users to access and plot important device properties.

Influence of the Dopant Penetration Depth on the Solar Cell Performance of n-type Interdigitated Back Contact Silicon Solar Cells

In this report a 2D modeling of n-type interdigitated back contact (IBC) crystalline silicon (c-Si) solar cell structures is presented for two different types of the BSF and emitter junctions: homojunction cells (referred as IBC-HOMO) and cells combining a homojunction and a heterojunction with hydrogenated amorphous silicon (a-Si:H), also called “hybrid” cells (referred as hybrid IBC). Both structures were analyzed and in particular we studied the effect of doping (peak concentration and penetration depth of the dopants) on the solar cell performances. For doping levels in the range 1018-1020 cm–3 relatively large dopant penetration depth (>100 nm) demonstrates better solar cell performance in contrary to very shallow penetration depths (10 nm). The best solar cell performance (25.6% conversion efficiency, 740 mV open circuit voltage, 41 mA/cm2 short circuit current and 84.2% fill factor) were found for hybrid IBC structures involving a BSF heterojunction and a highly doped emitter homojunction (NE = 1021 cm–3) with a dopant penetration depth of 10 nm in the case of n-type silicon wafer with a thickness of 100 μm. The implementation of defects at the c-Si/a-Si:H interface in the range (1-5)×1011 cm–2 shows that hybrid cells with BSF heterojunctions are more affected than the structures with emitter heterojunctions. However, solar cell efficiencies of 25% can be simulated for hybrid cells if the width of the BSF is reduced with respect to the emitter and combined with highly doped homojunctions and shallow dopant penetration depths.

Influence of ITO layer application on electrical parameters of silicon solar cells with screen printed front electrode

Purpose The purpose of this paper was investigation and comparison of electrical and optical properties of crystalline silicon solar cells with ITO or TiO2 coating. The ITO, similar to TiO2, is very well transparent in the visible part of optical radiation; however, its low resistivity (lower that 10-3 Ohm/cm) makes it possible to use simultaneously as a transparent electrode for collection of photo-generated electrical charge carriers. This might also invoke increasing the distance between screen-printed metal fingers at the front of the solar cell that would increase of the cell’s active area. Performed optical investigation showed that applied ITO thin film fulfill standard requirements according to antireflection properties when it was deposited on the surface of silicon solar cell. Design/methodology/approach Two sets of samples were prepared for comparison. In the first one, the ITO thin film was deposited directly on the crystalline silicon substrate with highly doped emitter region. In the second case, the TCO film was deposited on the same type of silicon substrate but with additional ultrathin SiO2 passivation. The fingers lines of 80 μm width were then screen-printed on the ITO layer with two different spaces between fingers for each set. The influence of application of the ITO electrode and the type of metal electrodes patterns on the electrical performance of the prepared solar cells was investigated through optical and electrical measurements. Findings The electrical parameters such as short-circuit current (Jsc), open circuit voltage (Voc), fill factor (FF) and conversion efficiency were determined on a basis of I-V characteristics. Short-circuit current density (Jsc) was equal to 32 mA/cm2 for a solar cell with a typical antireflection layer and 31.5 mA/cm2 for the cell with ITO layer, respectively. Additionally, electroluminescence of prepared cells was measured and analysed. Originality/value The influence of the properties of ITO electrode on the electrical performance of crystalline silicon solar cells was investigated through complex optical, electrical and electroluminescence measurements.

Low-frequency noise properties of p-type GaAs/AlGaAs heterojunction detectors

We have measured and analyzed, at different temperatures and bias voltages, the dark noise spectra of GaAs/AlGaAs heterojunction infrared photodetectors, where a highly doped GaAs emitter is sandwiched between two AlGaAs barriers. The noise and gain mechanisms associated with the carrier transport are investigated, and it is shown that a lower noise spectral density is observed for a device with a flat barrier, and thicker emitter. Despite the lower noise power spectral density of flat barrier device, comparison of the dark and photocurrent noise gain between flat and graded barrier samples confirmed that the escape probability of carriers (or detectivity) is enhanced by grading the barrier. The grading suppresses recombination owing to the higher momentum of carriers in the barrier. Optimizing the emitter thickness of the graded barrier to enhance the absorption efficiency, and increase the escape probability and lower the dark current, enhances the specific detectivity of devices.

Enhanced energy transfer by near-field coupling of a nanostructured metamaterial with a graphene-covered plate

Coupled surface plasmon/phonon polaritons and hyperbolic modes are known to enhance radiative transfer across nanometer vacuum gaps but usually require identical materials. It becomes crucial to achieve strong near-field energy transfer between dissimilar materials for applications like near-field thermophotovoltaic and thermal rectification. In this work, we theoretically demonstrate enhanced near-field radiative transfer between a nanostructured metamaterial emitter and a graphene-covered planar receiver. Strong near-field coupling with two orders of magnitude enhancement in the spectral heat flux is achieved at the gap distance of 20nm. By carefully selecting the graphene chemical potential and doping levels of silicon nanohole emitter and silicon plate receiver, the total near-field radiative heat flux can reach about 500 times higher than the far-field blackbody limit between 400K and 300K. The physical mechanism is elucidated by the near-field surface plasmon coupling with fluctuational electrodynamics and dispersion relations. The effects of graphene chemical potential, emitter and receiver doping levels, and vacuum gap distance on the near-field coupling and radiative energy transfer are analyzed in detail.

Emitter/absorber interface of CdTe solar cells

The performance of CdTe solar cells can be very sensitive to the emitter/absorber interface, especially for high-efficiency cells with high bulk lifetime. Performance losses from acceptor-type interface defects can be significant when interface defect states are located near mid-gap energies. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e., defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV ≤ ΔEC ≤ 0.3 eV) can help maintain good cell efficiency in spite of high interface defect density, much like with Cu(In,Ga)Se2 (CIGS) cells. The basic principle is that positive ΔEC, often referred to as a “spike,” creates an absorber inversion and hence a large hole barrier adjacent to the interface. As a result, the electron-hole recombination is suppressed due to an insufficient hole supply at the interface. A large spike (ΔEC ≥ 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a “cliff” (ΔEC &amp;lt; 0 eV) allows high hole concentration in the vicinity of the interface, which will assist interface recombination and result in a reduced open-circuit voltage. Another way to mitigate performance losses due to interface defects is to use a thin and highly doped emitter, which can invert the absorber and form a large hole barrier at the interface. CdS is the most common emitter material used in CdTe solar cells, but the CdS/CdTe interface is in the cliff category and is not favorable from the band-offset perspective. The ΔEC of other n-type emitter choices, such as (Mg,Zn)O, Cd(S,O), or (Cd,Mg)Te, can be tuned by varying the elemental ratio for an optimal positive value of ΔEC. These materials are predicted to yield higher voltages and would therefore be better candidates for the CdTe-cell emitter.