Solar Energy Research Institute of Sun Yat-sen University

Abstract Silicon heterojunction (SHJ) solar cells have reached high power conversion efficiency owing to their effective passivating contact structures. Improvements in the optoelectronic properties of these contacts can enable higher device efficiency, thus further consolidating the commercial potential of SHJ technology. Here we increase the efficiency of back junction SHJ solar cells with improved back contacts consisting of p-type doped nanocrystalline silicon and a transparent conductive oxide with a low sheet resistance. The electrical properties of the hole-selective contact are analysed and compared with a p-type doped amorphous silicon contact. We demonstrate improvement in the charge carrier transport and a low contact resistivity (<5 mΩ cm 2 ). Eventually, we report a series of certified power conversion efficiencies of up to 26.81% and fill factors up to 86.59% on industry-grade silicon wafers (274 cm 2 , M6 size).

As the photovoltaic (PV) industry heading towards the multi-TW scale, PV technologies need to be carefully evaluated based on material consumption rather than just efficiency or cost to ensure sustainable growth of the industry.

Abstract We present an industrial tunnel oxide passivated contacts (i‐TOPCon) bifacial crystalline silicon (c‐Si) solar cell based on large‐area n ‐type substrate. The interfacial thin SiO 2 is thermally growth and in situ capped by an intrinsic poly‐Si layer deposited by low‐pressure chemical vapor deposition (LPCVD). The intrinsic poly‐Si layer is doped in an industrial POCl 3 diffusion furnace to form the n + poly‐Si at the rear, which shows an excellent surface passivation characteristics with J 0 = 2.6 fA/cm 2 when passivated by a SiN x :H layer deposited by plasma‐enhanced chemical vapor deposition (PECVD). With an industrial fabrication process, the cells are manufactured with screen‐printed front and rear metallization, using large‐area 6‐in. n ‐type Czochralski (Cz) Si wafers. We demonstrate an average front‐side efficiency greater than 23% and an open‐circuit voltage V oc greater than 700 mV. These results are based on more than 20 000 pieces of cells from mass production on a single day, in an old conventional multicrystalline silicon (mc‐Si) Al‐back surface field (BSF) cell workshop, which has been upgraded to i‐TOPCon process. The best cell efficiency reaches 23.57%, as independently confirmed by Fraunhofer CalLab. A median module power greater than 345 W and a best module power greater than 355 W are demonstrated with double‐glass bifacial i‐TOPCon modules consisting of 120 pieces of half‐cut 161.7 mm pseudosquare i‐TOPCon cells with nine busbars.

In this study, a NiO-based resistive memristor was manufactured using a solution combustion method. In this device, both analog and digital bipolar resistive switching were observed. They are dependent on the stressed bias voltage. Prior to the electroforming, the analog bipolar resistive switching was realized through the change of the Schottky barrier at p-type NiO/Ag junction by the local migration of the oxygen ion in the interface. On the basis of the analog resistive switching, several synaptic functions were demonstrated, such as nonlinear transmission characteristics, spike-rate-dependent plasticity, long-term/short-term memory, and "learning-experience" behavior. In addition, once the electroforming operation was carried out using a high applied voltage, the resistive switching was changed from analog to digital. The formation and rupture of the oxygen vacancy filaments is dominant. This novel memristor with the multifunction of analog and digital resistive switching is expected to decrease the manufacturing complexity of the electrocircuits containing analog/digital memristors.

Abstract A highly transparent passivating contact (TPC) as front contact for crystalline silicon (c-Si) solar cells could in principle combine high conductivity, excellent surface passivation and high optical transparency. However, the simultaneous optimization of these features remains challenging. Here, we present a TPC consisting of a silicon-oxide tunnel layer followed by two layers of hydrogenated nanocrystalline silicon carbide (nc-SiC:H(n)) deposited at different temperatures and a sputtered indium tin oxide (ITO) layer (c-Si(n)/SiO 2 /nc-SiC:H(n)/ITO). While the wide band gap of nc-SiC:H(n) ensures high optical transparency, the double layer design enables good passivation and high conductivity translating into an improved short-circuit current density (40.87 mA cm −2 ), fill factor (80.9%) and efficiency of 23.99 ± 0.29% (certified). Additionally, this contact avoids the need for additional hydrogenation or high-temperature postdeposition annealing steps. We investigate the passivation mechanism and working principle of the TPC and provide a loss analysis based on numerical simulations outlining pathways towards conversion efficiencies of 26%.

Quantifying recombination in halide perovskites is a crucial prerequisite to control and improve the performance of perovskite-based solar cells. While both steady-state and transient photoluminescence are frequently used to assess recombination in perovskite absorbers, quantitative analyses within a consistent model are seldom reported. We use transient photoluminescence measurements with a large dynamic range of more than ten orders of magnitude on triple-cation perovskite films showing long-lived photoluminescence transients featuring continuously changing decay times that range from tens of nanoseconds to hundreds of microseconds. We quantitatively explain both the transient and steady-state photoluminescence with the presence of a high density of shallow defects and consequent high rates of charge carrier trapping, thereby showing that deep defects do not affect the recombination dynamics. The complex carrier kinetics caused by emission and recombination processes via shallow defects imply that the reporting of only single lifetime values, as is routinely done in the literature, is meaningless for such materials. We show that the features indicative for shallow defects seen in the bare films remain dominant in finished devices and are therefore also crucial to understanding the performance of perovskite solar cells.

To meet the target set by the Paris agreement in 2015 to keep the Earth average temperature rise to less than 2 °C (or even 1.5 °C), the best choice is to transition the energy economy to 100% renewable energy using solar photovoltaic energy (PV), playing a central role along with wind, hydro, geothermal, and biomass energy, to power directly or indirectly all sectors of the economy. The development of a large global energy storage capacity and the production of green hydrogen or other synthetic fuels by renewable energy will be critical. The estimated needed global PV generating capacity will be about 70 TW by 2050. The PV industry needs to rapidly grow its production capacity to about 3 TW p.a. to reach this objective. The industry has demonstrated that it is capable to grow at a very high rate and to continuously reduce the cost of manufacturing. There are no challenges related to the technology, manufacturing cost, or sustainability, except for the consumption of silver, which needs to be reduced by at least a factor of 4, and the recycling of material used in the PV system, which needs to be dramatically improved. The deployment of PV systems must be accelerated to reach a fast growth (>25%) until at least 2032 to avoid a major market downturn in 2050.

While halide perovskites have excellent optoelectronic properties, their poor stability is a major obstacle toward commercialization. There is a strong interest to move away from organic A-site cations such as methylammonium and formamidinium toward Cs with the aim of improving thermal stability of the perovskite layers. While the optoelectronic properties and the device performance of Cs-based all-inorganic lead-halide perovskites are very good, they are still trailing behind those of perovskites that use organic cations. Here, the state-of-the-art of all-inorganic perovskites for photovoltaic applications is reviewed by performing detailed meta-analyses of key performance parameters on the cell and material level. Key material properties such as carrier mobilities, external photoluminescence quantum efficiency, and photoluminescence lifetime are discussed and what is known about defect tolerance in all-inorganic is compared relative to hybrid (organic-inorganic) perovskites. Subsequently, a unified approach is adopted for analyzing performance losses in perovskite solar cells based on breaking down the losses into several figures of merit representing recombination losses, resistive losses, and optical losses. Based on this detailed loss analysis, guidelines are eventually developed for future performance improvement of all-inorganic perovskite solar cells.

Abstract Semitransparent perovskite solar cells (st‐PSCs) have received remarkable interest in recent years because of their great potential in applications for solar window, tandem solar cells, and flexible photovoltaics. However, all reported st‐PSCs require expensive transparent conducting oxides (TCOs) or metal‐based thin films made by vacuum deposition, which is not cost effective for large‐scale fabrication: the cost of TCOs is estimated to occupy ≈75% of the manufacturing cost of PSCs. To address this critical challenge, this study reports a low‐temperature and vacuum‐free strategy for the fabrication of highly efficient TCO‐free st‐PSCs. The TCO‐free st‐PSC on glass exhibits 13.9% power conversion efficiency (PCE), and the four‐terminal tandem cell made with the st‐PSC top cell and c‐Si bottom cell shows an overall PCE of 19.2%. Due to the low processing temperature, the fabrication of flexible st‐PSCs is demonstrated on polyethylene terephthalate and polyimide, which show excellent stability under repeated bending or even crumbing.

Defects passivation is widely devoted to improving the performance of formamidinium lead triiodide perovskite solar cells; however, the effect of various defects on the α-phase stability is still unclear. Here, using density functional theory, we first reveal the degradation pathway of the formamidinium lead triiodide perovskite from α to δ phase and investigate the effect of various defects on the energy barrier of phase transition. The simulation results predict that iodine vacancies are most likely to trigger the degradation, since they obviously reduce the energy barrier of α-to-δ phase transition and have the lowest formation energies at the perovskite surface. A water-insoluble lead oxalate compact layer is introduced on the perovskite surface to largely suppress the α-phase collapse through hindering the iodine migration and volatilization. Furthermore, this strategy largely reduces the interfacial nonradiative recombination and boosts the efficiency of the solar cells to 25.39% (certified 24.92%). Unpackaged device can maintain 92% of its initial efficiency after operation at maximum power point under simulated air mass 1.5 G irradiation for 550 h.

Abstract The explosion of mobile data from the internet of things (IoT) is leading to the emergence of 5G technology with dramatic frequency band expansion and efficient band allocations. Along with this, the demand for high‐performance filters for 5G radio frequency (RF) front‐ends keeps growing. The most popular 5G filters are constructed by piezoelectric resonators based on AlN semiconductor. However, AlN possesses a piezoelectric constant d 33 lower than 5 pm V −1 and it becomes necessary to develop novel semiconductors with larger piezoelectric constant. In this work, it is shown that strong piezoelectricity exists in ε ‐Ga 2 O 3 . High‐quality phase‐pure ε ‐Ga 2 O 3 thin films with a relatively low residual stress are prepared. A switching spectroscopy piezoelectric force microscope (SS‐PFM) measurement is carried out and the piezoelectric constant d 33 of ε ‐Ga 2 O 3 is determined to be ≈10.8–11.2 pm V −1 , which is twice as large as that of AlN. For the first time, surface acoustic wave (SAW) resonators are demonstrated on the ε ‐Ga 2 O 3 thin films and different vibration modes resonating in the GHz range are observed. The results suggest that ε ‐Ga 2 O 3 is a great material candidate for application in piezoelectric devices, thanks to its wide bandgap, strong piezoelectric property, small acoustic impedance, and low residual stress.

The certified efficiency of perovskite solar cells (PSCs) has reached 25.5% within just around 10 years, approaching the highest reported value of mainstream silicon solar cells. The application of metal–oxide (MO) electron transport layers (ETLs), including TiO 2 and SnO 2 , is crucial for achieving highly efficient PSCs because of their wonderful photoelectrical properties, resulting in n–i–p conventional structure devices, constantly breaking the world record efficiency. However, these MOETLs inevitably lead to the degradation of PSCs due to their photocatalytic activity under actual sunlight which includes ultraviolet (UV) range. Overcoming the UV photocatalytic degradation is still a great challenge for the state‐of‐the‐art PSCs toward practical applications. Herein, the recent progress related to the UV photocatalytic degradation of PSCs induced by the MOETLs based on recent literature reports is reviewed, including the photocatalysis origin, degradation mechanism, challenges, and various strategies. Perspectives for future efforts in overcoming UV photocatalytic degradation are provided. It is believed that this review is advantageous for achieving stable PSCs under actual outdoor sunlight.

The present study investigates the electrical properties of transition metal oxide (TMO) emitters in dopant‐free n‐Si back contact solar cells by comparing the properties of solar cells employing three TMOs (WO x , MoO x and V 2 O x ) with varying electrical properties acting as p‐type contacts. The TMOs are found to induce large band bending in n‐Si, which reduces the injection level dependent interfacial recombination speed S eff and contact resistivity ρ c . Among the TMO/n‐Si contacts considered, the V 2 O x /n‐Si contact achieves the lowest S eff of 138 cm/s and ρ c of 0.034 Ω cm 2 , providing the significant advantages over heavily doped a‐Si:H(p)/n‐Si contacts. The best device performance was achieved by the V 2 O x /n‐Si solar cell, demonstrating an efficiency of 16.59% and an open‐circuit voltage of 610 mV relative to solar cells based on MoO x /n‐Si (15.09%, 594 mV) and WO x /n‐Si (12.44%, 539 mV). Furthermore, the present work is the first to employ WO x , V 2 O x and Cs 2 CO 3 in back contact solar cells. The fabrication process employed offers great potential for the mass production of back contact solar cells owing to simple, metal mask patterning with high alignment quality and dopant‐free steps conducted at a lower temperature.

Crystalline-silicon heterojunction back contact solar cells represent the forefront of photovoltaic technology, but encounter significant challenges in managing charge carrier recombination and transport to achieve high efficiency. In this study, we produced highly efficient heterojunction back contact solar cells with a certified efficiency of 27.09% using a laser patterning technique. Our findings indicate that recombination losses primarily arise from the hole-selective contact region and polarity boundaries. We propose solutions to these issues and establish a clear relationship between contact resistivity, series resistance, and the design of the rear-side pattern. Furthermore, we demonstrate that the wafer edge becomes the main channel for current density loss caused by carrier recombination once electrical shading around the electron-selective contact region is mitigated. With the advanced nanocrystalline passivating contact, wafer edge passivation technologies and meticulous optimization of front anti-reflection coating and rear reflector, achieving efficiencies as high as 27.7% is feasible. The management of charge carrier recombination and transport in heterojunction back contact solar cells poses significant challenges in achieving a high efficiency. Here, authors analyze various loss mechanisms of devices fabricated by laser patterning, and achieve a certified efficiency of 27.09%.

Layer-by-layer morphology is a crucial signature of the quality of epitaxial thin films. In this study, layer-by-layer growth of an ε-phase gallium oxide (ε-Ga2O3) thin film is demonstrated using metal–organic chemical vapor deposition. A two-step growth method, in which a nucleation layer is grown at 600 °C and an epilayer is grown at 640 °C, is employed to fabricate a high-quality ε-Ga2O3 thin film on a c-plane sapphire substrate. The morphology of the ε-Ga2O3 film is evaluated by atomic force microscope. The density of screw-type threading dislocations determined by an X-ray diffraction rocking curve is as low as 1.8 × 108 cm−2.

Here, we demonstrate the in situ growth of SnO2 nanosheets on a freestanding carbonized eggshell membrane (CEM), which provides three-dimensional, bicontinuous electron and ion transport pathways through a massively interconnected carbon fiber skeleton and interpenetrated pore network, respectively. This CEM has other advantages such as the ability to alleviate mechanical stress during cycling as a buffer matrix. When used as an additive-free anode in a sodium-ion battery, SnO2 nanosheets can realize a complete electrochemical reaction and maintain good cycling stability with the help of a CEM. For instance, SnO2 nanosheets delivered a high reversible capacity of 656 mA h g–1 in the 5th cycle at 0.1 A g–1, approaching 98% of its theoretical specific capacity, and maintained a high reversible specific capacity of 420 mA h g–1 after 200 cycles at 0.2 A g–1.

Efficiency and manufacturing cost are two key elements for the photovoltaic (PV) industry. In this paper, we look at the time-dependent evolution of efficiency and manufacturing cost for PV devices. For efficiency improvements, the empirical model developed by Goetzberger et al. is applied to describe the time-dependent improvements for a concrete technology in laboratory cell's research and development, and the learning factor c is extracted. The application of the Goetzberger's model is extended to industrial PV modules. It is forecasted that cadmium telluride (CdTe) and copper gallium indium diselenide (CIGS) will have the average module efficiency in 2020 of 17.9% and 16.4%, respectively. Over 21.8% commercial module efficiency is projected with n-type Si interdigitated back contact technology, while average module efficiencies of 17.4%, 18.4%, and 19.4% are projected for conventional p-type multi-, mono-, and mono-passivated emitter and rear cell (PERC), respectively. For the manufacturing cost, we parameterized the learning curve model of manufacturing cost for industrial crystalline silicon (c-Si), CdTe, and CIGS technologies. As projected by the learning curve, the manufacturing cost of c-Si and thin-film modules may reach 0.2 $/Wp or below, when the cumulative production reach 1 TW. The learning rate for Si (24.2%) is greater than CdTe (19.1%) and CIGS (8.1%).

Novel multilayer back contact (MLBC) solar cells employing V₂O_x (8 nm)/metal/V₂O_x (8 nm) multilayers achieve an efficiency of 19.02%.

Interconnected MoS₂ nanosheets were grown on Ti foil <italic>via</italic> a self-supported TiO₂ bonding interface to preferentially expose the active edge sites.

A high recombination rate and high thermal budget for aluminum (Al) back surface field are found in the industrial p-type silicon solar cells. Direct metallization on lightly doped p-type silicon, however, exhibits a large Schottky barrier for the holes on the silicon surface because of Fermi-level pinning effect. As a result, low-temperature-deposited, dopant-free chromium trioxide (CrOx, x < 3) with high stability and high performance is first applied in a p-type silicon solar cell as a hole-selective contact at the rear surface. By using 4 nm CrOx between the p-type silicon and Ag, we achieve a reduction of the contact resistivity for the contact of Ag directly on p-type silicon. For further improvement, we utilize a CrOx (2 nm)/Ag (30 nm)/CrOx (2 nm) multilayer film on the contact between Ag and p-type crystalline silicon (c-Si) to achieve a lower contact resistance (40 mΩ·cm2). The low-resistivity Ohmic contact is attributed to the high work function of the uniform CrOx film and the depinning of the Fermi level of the SiOx layer at the silicon interface. Implementing the advanced hole-selective contacts with CrOx/Ag/CrOx on the p-type silicon solar cell results in a power conversion efficiency of 20.3%, which is 0.1% higher than that of the cell utilizing 4 nm CrOx. Compared with the commercialized p-type solar cell, the novel CrOx-based hole-selective transport material opens up a new possibility for c-Si solar cells using high-efficiency, low-temperature, and dopant-free deposition techniques.