Thin Film Photovoltaic Research Articles

Human-friendly semitransparent organic solar cells achieving high performance

We systematically evaluated the photobiological safety of mainstream ST-PV devices and fabricated a series of high-performance human-friendly ST-PV devices with LUE values exceeding 5.0% and low skin/eye damage levels for human beings.

Origin of sputter damage during transparent conductive oxide deposition for semitransparent perovskite solar cells

The origin of sputter damage during transparent conductive oxide deposition is ion bombardment rather than plasma radiation. Ion bombardment increased recombination, whereas plasma radiation reduced recombination.

Collaborative regulation strategy of donor and acceptor analogues realizes multifunctional semitransparent organic solar cells with excellent comprehensive performance

We propose a collaborative regulation strategy of donor and acceptor analogues to develop multi-functional ST-OSCs with highly comprehensive performance.

Efficient and stable semitransparent perovskite photovoltaics via a Lewis base incorporation.

Semitransparent perovskite solar cells (ST-PSCs) have great potential in building integrated photovoltaics. However, semitransparent devices suffer from a low electron mobility and an imbalanced charge-carrier transport, leading to an unsatisfactory power conversion efficiency (PCE) and limited stability. Herein, we report a high-performance ST-PSC via the incorporation of a special Lewis base. A better perovskite with an improved crystallinity and less defects was achieved, and a matched energy level alignment between the perovskite and [6,6]-phenyl-C61-butyric acid methyl ester was also induced, thereby leading to a high electron mobility and an exceptional balance of hole and electron mobility approaching 1 : 1. The prepared ST-PSC exhibited a PCE of 20.22% at average visible transmittance (AVT) of 4.93%, 18.32% at AVT of 14.38%, and 15.00% at AVT of 25.65%. These PCEs are the highest values among those ST-PSCs based on top metallic electrodes at a close AVT. The ST-PSCs maintained 92% of the initial PCE in storage for 1000 h, and they held 84% of the initial PCE under the continuous maximum power point tracking measurement for 530 hours. The work paves the way to realize ST-PSCs with a high PCE, high light utilization efficiency and substantially enhanced stability.

An electrochemical impedance study to analyse the phase transformation pattern and stability during electro-crystallization of CIGS photo-voltaic thin films

In this study, an effort has been made to gain a thorough knowledge of the phase transformation mechanism of quaternary thin films Cu (In, Ga) Se2 on FTO-glass substrates through electrochemical impedance spectroscopy (EIS). Here, a methodical strategy that starts with the investigation of unitary (Cu, Se, In and Ga), binary (Cu-In, Cu-Se, Cu-Ga, In-Se, In-Ga, and Se-Ga), tertiary (Cu-In-Se, Cu-In-Ga, In-Se-Ga, and Cu-Se-Ga), and finally quaternary (Cu-In-Ga-Se) deposition has been put forward. CuCl2, H2SeO4, InCl3, and GaCl3 were the salts utilized, and their combinations for each stage of deposition. The information obtained from EIS i.e., solution resistance (Rs), double layer capacitance (Cdl), charge transfer resistance (Rct), film resistances (Rfilm), and film capacitances (Cfilm) were used to find the mechanism. For unitary baths, Cu has the highest Rct and high Cdl under the optimized concentration. Binary baths further explained that Se-Ga and In-Ga can be used to perform one stage of deposition considering the low Rct and moderate Cdl. The tertiary bath combinations favored CIS as one stage of deposition in a similar manner (i.e., low Rct and Cdl). While using the quaternary bath, Rct and Cdl were found to have values of 483.6 Ω.cm2 and 285.78 µF/cm2. From the impedance pattern, it was deduced that the deposition takes place in two layers i.e., CIS and CGS tertiary films which eventually give the quaternary composition. Further, the stability of the films was also evaluated in the Na2SO4 solution, the CIGS film is found to be sufficiently stable.

Figure-of-merit for assessment of semitransparent solar cells

Figure-of-merit for assessment of semitransparent solar cells

The buffer – Free semitransparent perovskite solar cells with ion-beam sputtered back electrode

Semitransparent perovskite solar cells (PSCs) have the potential for utilization in tandem photovoltaics (PV) and see-through PV for building integration. The passage of light through the thin-film device structure requires transparent contact at the front and back sides of the device. Typically, transparent contacts are made of wide bang-gap conductive oxides (In2O3:SnO2(ITO), etc.) deposited by magnetron sputtering (MS). The use of conventional MS usually requires the addition of a buffer layer to avoid the damage of the charge transporting layers. In this work, the semitransparent perovskite solar cell with p-i-n architecture is fabricated with ITO back electrode deposited directly on C60 electron transporting layer. A comparative analysis was conducted to evaluate the performance and properties of ITO films deposited using ion-beam sputtering (IBS) and the more common MS method. The IBS process was found to eliminate plasma-substrate interaction, resulting in improved deposition on organic layers. Conversely, the MS method resulted in poor output performance and S-shaped IV characteristics of the semitransparent-PSCs. By utilizing IBS fabrication for the back electrode, the relevant efficiency of 12.65% was achieved for the best device. The changes in chemical, optical, and transport properties of the ITO samples fabricated with different methods were investigated. This study represents the first successful utilization of ion-beam sputtering for the fabrication of semitransparent PSCs.

High-performance semi-transparent organic solar cells driven by the dipole-controlled optoelectrical response of bilateral self-assembled monolayer strategy

A bilateral self-assembled monolayer (SAM) strategy is proposed to improve the performance of both opaque/translucent and rigid/flexible organic solar cells (OSCs), which have great potential for various high-value applications such as portable, building-integrated and vehicle-integrated photovoltaics. By applying the dipole-controlled SAMs to both ITO/ZnO and ZnO/active layer interfaces, the work function of the ZnO electron transport layer was reduced, which improved charge transport and reduced carrier recombination at the interface. The opaque OSCs with the bilateral SAM demonstrated significant performance improvement with power conversion efficiencies (PCEs) reaching 17.20% and 16.96% for rigid and flexible OSCs. When used in semi-transparent OSCs together with MoO3/Ag/MoO3 electrode, in semi-transparent (ST) OSCs, PCE and average visible transmittance (AVT) can be improved simultaneously, and 10.37% PCE and 36.27% AVT demonstrate a remarkable light utilization efficiency (LUE) of 3.85%. Finally, the large area (10 × 10 cm2) ST-OSC module was fabricated and demonstrated a PCE of 8.17% and LUE of 2.5%, among the best-reported values for inverted module devices. The developed bilateral SAM strategy can be useful in developing high-performance OSCs of both opaque/translucent and rigid/flexible types for various practical applications.

High-performance and selective semi-transparent perovskite solar cells using 3D-structured FTO

Perovskite solar cells (PSCs) have been in the spotlight as a promising next-generation solar cell. With the tremendous development of power conversion efficiency (PCE) over the past decades, a considerable amount of research has focused on semi-transparent perovskite solar cells for applications. However, the short-circuit current density (JSC) greatly decreases in semi-transparent PSCs with an increase in transmittance, and this results in a significant decrease in PCE. In this study, semi-transparent PSCs were fabricated by controlling the absorption layer thickness and aperture ratio using a 3D-structured FTO manufactured via processes that can work large areas (direct printing and mist-CVD). This strategy has an advantage in that the aperture ratio (transmission/entire area) can be controlled easily by adjusting pattern specification. The effect of a 3D-structured FTO enhanced the diffuse transmittance and shortened the carrier travel distance; further, it minimized the decrease in PCE because of an increase in transmittance. Our fully semi-transparent PSCs (F–PSCs) with the ITO cathode achieved a PCE of 12.0 %–14.6 %, and an average visible transmittance (AVT) of 13.4 %–17.0 %. These results demonstrate that the parameter of semi-transparent PSCs (transmittance and PCE) can be easily tailored to the application by controlling the specification of the pattern.

Single-component organic solar cells-Perspective on the importance of chemical precision in conjugated block copolymers.

Organic photovoltaics (OPV) present a promising thin-film solar cell technology with particular benefits in terms of weight, aesthetics, transparency, and cost. However, despite being studied intensively since the mid 90's, OPV has not entered the mass consumer market yet. Although the efficiency gap with other thin-film photovoltaics has largely been overcome, active layer stability and performance reproducibility issues have not been fully resolved. State-of-the-art OPV devices employ a physical mixture of electron donor and acceptor molecules in a bulk heterojunction active layer. These blends are prone to morphological changes, leading to performance losses over time. On the other hand, in "single-component" organic solar cells, the donor and acceptor constituents are chemically connected within a single material, preventing demixing and thereby enhancing device stability. Novel single-component materials affording reasonably high solar cell efficiencies and improved lifetimes have recently emerged. In particular, the combination of donor and acceptor structures in conjugated block copolymers (CBCs) presents an exciting approach. Nevertheless, the current CBCs are poorly defined from a structural point of view, while synthetic protocols remain unoptimized. More controlled synthesis followed by proper structural analysis of CBCs is, however, essential to develop rational structure-property-device relations and to drive the field forward. In this perspective, we provide a short overview of the state-of-the-art in single-component organic solar cells prepared from CBCs, reflect on their troublesome characterization and the importance of chemical precision in these structures, give some recommendations, and discuss the potential impact of these aspects on the field.

Tunneling-enhanced interface recombination and current loss curves in kesterite solar cells

An approach to developing durable, light-weight, flexible, and semi-transparent solar cells is through the utilization of Cu2ZnSnS4 (CZTS) monograin powder. However, CZTS cells are currently far from their theoretically predicted efficiency. One reason for this is tunneling-enhanced interface recombination, which leads to a decrease in VOC and FF under higher forward bias conditions. We calculated the current loss curves JR–V of three different CZTS monograin layer solar cells for this report by subtracting the dark J–V curve from the light curve and adding a short circuit current density JSC. By quantum tunneling of holes through a bell-shaped potential barrier with additional recombination at the interface between CdS and CZTS, the shape of the current loss curve was examined. We showed that using the derivative dJR/dV of the measured curves allows us to simplify our analysis. The maximum position of this curve is proportional to the effective barrier height, and the intensity and the full width at half maximum give information about the width. At lower temperatures, the effective barrier height increases according to our theoretical model. We demonstrated that the properties of CZTS solar cells may be significantly enhanced by eliminating current loss at higher bias voltages.

MXene‐Interconnected Two‐Terminal, Mechanically‐Stacked Perovskite/Silicon Tandem Solar Cell with High Efficiency

AbstractTwo‐terminal, mechanically‐stacked perovskite/silicon tandem solar cells offer a feasible way to achieve power conversion efficiencies (PCEs) of over 35%, provided that the state‐of‐the‐art industrial silicon solar cells and perovskite solar cells (PSCs) are fully compatible with one another. Herein, two‐terminal, mechanically‐stacked perovskite/silicon tandem solar cells are developed by mechanically interconnecting semitransparent PSCs and TOPCon solar cells with a MXene interlayer. The semitransparent PSCs are made from wide‐bandgap perovskite Cs0.15FA0.65MA0.20Pb(I0.80Br0.20)3 films. Furthermore, the co‐additives KPF6 and CH3NH3Cl(MACl) are employed to reduce grain boundaries and intragranular defects in the perovskite, boosting the PCE of the semitransparent PSCs to a record‐high value of 20.96% under reverse scan (RS) through a reduction in non‐radiative recombination probability. These optimized semitransparent PSCs are then employed in MXene‐interconnected two‐terminal, mechanically‐stacked tandem solar cells. The enhanced interfacial carrier transportation, with minimal influence on light transmission, imparted by the MXene flakes allows the tandem solar cells to achieve a stabilized PCE of 29.65%. The tandem cells also exhibit acceptable operational stability and are able to retain ≈93% and 92% of their initial PCEs after 120 min of continuous illumination or storage in ambient air for 1000 h, respectively.

Development of semitransparent CdTe polycrystalline thin-film solar cells modified with a CuCl layer for BIPV

In the current context of renewable energy development, CdTe polycrystalline thin-film solar cells are expected to have broad prospects in fields such as Building Integrated Photovoltaics. It is crucial to fabricate sub-micron-thick, semitransparent CdTe solar cells for photovoltaic glass curtain walls that require a certain degree of transparency. As a result, we have employeded a high-quality deposition technique for sub-micron-thick CdTe polycrystalline films. We have analyzed the influence of post-treatment processes on the film properties and investigated the impact of solution-based CuCl back buffer layer preparation on device performance. By improving the quality of sub-micron-thick CdTe polycrystalline films, and optimizing the concentration and process of Cu doping, we have successfully fabricated semitransparent CdTe solar cells with an average visible light transmittance of 14.21%, ηFront: 6.2%, ηRear: 4.4%, and bifacial factor:0.7.

Effects of the Electrical Properties of SnO2 and C60 on the Carrier Transport Characteristics of p-i-n-Structured Semitransparent Perovskite Solar Cells.

Recently, metal halide perovskite-based top cells have shown significant potential for use in inexpensive and high-performance tandem solar cells. In state-of-the-art p-i-n perovskite/Si tandem devices, atomic-layer-deposited SnO2 has been widely used as a buffer layer in the top cells because it enables conformal, pinhole-free, and highly transparent buffer layer formation. In this work, the effects of various electrical properties of SnO2 and C60 layers on the carrier transport characteristics and the performance of the final devices were investigated using a numerical simulation method, which was established based on real experimental data to increase the validity of the model. It was found that the band alignment at the SnO2/C60 interface does, indeed, have a significant impact on the electron transport. In addition, as a general design rule, it was suggested that at first, the conduction band offset (CBO) between C60 and SnO2 should be chosen so as not to be too negative. However, even in a case in which this CBO condition is not met, we would still have the means to improve the electron transport characteristics by increasing the doping density of at least one of the two layers of C60 and/or SnO2, which would enhance the built-in potential across the perovskite layer and the electron extraction at the C60/SnO2 interface.

Semitransparent Organic Solar Cells with Homogeneous Transmission and Colorful Reflection Enabled by an ITO-Free Microcavity Architecture.

Semitransparent organic photovoltaics (ST-OPVs), owing to the merits of high power generation, thermal insulation, and aesthetic features, have become a promising candidate for intellectual building- integrated photovoltaic windows. However, the traditional optical evaluation only focuses on the transmission properties and ignores the reflection behaviors. And the lack of quantitative descriptions for array appearance hinders implementation of ST-OPV based large-area modules. To tackle with these issues, an indium tin oxide (ITO)-free optical microcavity architecture into ST-OPVs for achieving high homogeneity in transmittance with controllable reflective appearances through tunning the thickness of individual component layers is introduced. A set of parameters based on optical characteristics of sub-units to provide a quantitative description for the transmittance brightness, transmissive and reflective color purity, and versatility of optical arrays, is further proposed. The optical simulations reveal that reflection modulation from blue to red colors can be realized for devices based on various bulk-heterojunction material systems through regulating the thickness of active layers and antireflection coatings. This work offers a viable design strategy for ST-OPVs toward applications in next-generation smart photovoltaic windows.

How backreflection contributes to light absorption for high-performance radial junction photovoltaics

A robust radial junction (RJ) structure directly constructed upon the surface of a flexible Al foil substrate shows a promising potential to boost wearable and portable applications, where the silicon nanowire (SiNW) supported multilayer has proven beneficial in excellent mechanical stability and sufficient light harvesting. Assigned to the beneficial backreflection contributed by the Al foil, a much larger light current can be achieved than that on glass. While a comprehensive understanding of the light absorption under the backreflection of the substrate remains mainly unexplored. Herein, a straightforward comparison of light absorption of RJ units on Al and glass substrates, within a theoretical framework based on a finite-element simulation, is performed. Then, taking SiNW geometric parameters and i-layer thickness into account, the evolutions of light harvesting and the external quantum efficiency curves are systematically studied. These results indicate that, under the backreflection of the substrate, the light absorption shows a reduced dependency on SiNW geometry and i-layer thickness to some extent, laying a critical basis to establish a simpler/easier fabrication process for high-performance flexible RJ thin film photovoltaics.

Can Lead-Free Double Halide Perovskites Serve as Proper Photovoltaic Absorber?

The emerging Pb-free double perovskites (DPs) are acknowledged as the most potential nontoxic alternatives to lead halide perovskites for thin-film photovoltaics, yet their photophysical properties significantly lag behind expectations. To tackle this issue, it is imperative to conduct a systematic investigation of the structure and optoelectronic properties and to sift through vast chemical space to extract new types of Pb-free DPs with exceptional optoelectronic characteristics and thermal stability. Through high-throughput first-principal calculations, we demonstrate that apart from a select few Pb-free DPs (e.g., Cs2InSbCl6 and Cs2TlBiBr6), other categories, even with suitable direct electronic bandgaps, exhibit inferior optical absorption due to the inversion symmetry-induced parity-forbidden transitions. The mismatch between the electronic and optical bandgap, thence, casts doubt on the reliability of the electronic bandgap as a criterion for Pb-free DPs in various optoelectronics. The assessed limited thermostability under operational conditions, however, hinders any Pb-free DPs from effectively serving as photovoltaic absorbers. Alongside the compositional engineering discussed above, the prospect of manipulating local-site symmetry and disrupting the parity forbidden transitions in stabilized Pb-free DPs through materials engineering should be recognized as a pivotal and rational avenue toward achieving high performance.

Exploring the impact of different annealing conditions on physical properties of CdSeTe thin films for solar cell absorber layer applications

The perovskite and Silicon based single junction solar cells certainly showed higher efficiency but the perovskite solar cells are highly degradable and unstable in environment whereas conventional Silicon solar cells are relatively costly. The CdTe absorber based thin film solar cells have attained efficiency of greater than 22% where doping of Selenium into the CdTe absorber layer seems to improve the photovoltaic performance. The CdCl2 treatment is proven to be critical process which induces the grain growth and recrystallization in CdSeTe films. Thus herein, air and CdCl2 annealing is performed over thermally evaporated CdSeTe thin films to seek out their applicability as an effective absorber for Cd-based thin film photovoltaics. The XRD diffractograms exposed the appearance of cubic phase with (111) preferred orientation where crystallite size is increased with annealing temperature. The optical absorbance is found to be altered with temperature of annealing and Tauc’s plots exhibited that bandgap is found to be changed in the range of 1.40–1.52 eV with increasing annealing temperature. Electrical analysis divulges Ohmic character of films where electrical resistivity and conductivity are affected by nature and temperature of post-deposition annealing. The EDS patterns confirmed the deposition of CdSeTe thin films and post deposition CdCl2 activation treatment. The FESEM images demonstrated alteration in surface morphology by grain growth where the grain size of CdSeTe films is increased from 70 nm to 235 nm with CdCl2 annealing temperature. The findings confirm that annealed CdSeTe thin films showed demanding behavior for solar cell devices as prominent light harvesting absorber layers.

Optical enhancement in perovskite thin films using moth-eye anti-reflection film

Perovskite solar cells represent an emerging photovoltaic technology. With the latest record efficiencies exceeding 25% coupled with low fabrication cost and tunable transparency, perovskite solar cells demonstrate promising applications as solar windows. For these applications, the perovskite solar cells need to be semi-transparent to allow incident light to pass through the windows while generating electricity. However, semi-transparency compromises light absorption in the solar cells. In this work, optical enhancement in perovskite thin films using moth-eye anti-reflection (AR) film is investigated. Perovskite thin films with different thicknesses are used and the thickness is controlled by varying the spin speeds during the deposition of the perovskite precursor. The optical effects in the perovskite films without and with moth-eye AR film are studied. From the findings, the reflection loss is reduced by maximum of ∼4%, which contributes to a higher light absorption in the perovskite layer, due to the AR effect of the moth-eye structure. These results imply that the moth-eye film can be a promising and facile alternative for developing a highly efficient and semi-transparent perovskite solar cell with a thin absorber layer.

X-ray Investigation of CsPbI3:EuCl3 Infiltrated into Gig-Lox TiO2 Spongy Layers for Perovskite Solar Cells Applications.

In this study, we explore the potential of a blended material comprising CsPbI3:EuCl3 perovskite and Gig-Lox TiO2, a unique transparent spongy material known for its multi-branched porous structure, for application in solar cells. The inclusion of EuCl3 in CsPbI3 serves to stabilize the photoactive γ-phase with a bandgap of 1.75 eV, making it suitable for solar energy conversion in tandem solar cells. Our study applies X-ray-based techniques to investigate the structural properties and interfacial behavior within this blended material, in comparison with a reference perovskite layer deposited on glass. In addition, Spectroscopic ellipsometry is complemented with density functional theory calculations and photoluminescence measurements to elucidate the absorption and radiative emission properties of the blend. Notably, our findings reveal a significant quenching of photoluminescence within the blended material, underscoring the pivotal role of the distributed interfaces in facilitating efficient carrier injection from the CsPbI3:EuCl3 perovskite into the Gig-Lox TiO2 sponge. These findings pave the way for the application of the blend as an Electron Transport Layer (ETL) in semi-transparent perovskite solar cells for tandem and building integrated photovoltaics.