The performance of dye-sensitized solar cells (DSCs) could be improved by using rationally designed mesoporous film structure for electron collection, dye adsorption and light scattering. The development of a novel double layer film prepared by TiO2 hierarchical submicrospheres and nanoparticles was reported in this article. The submicrospheres were composed of rutile nanorods of 10 nm diameter and the length of 150–250 nm, which facilitated fast electron transport, charge collection and light scattering. Using a double layer structure consisting of the 10 wt% film as a dye loading layer and the 50 wt% film as the light scattering layer, C101 sensitizer and liquid electrolyte, DSC yielded power conversion efficiency of 9.68% under 1 sun illumination.

•Upper-limited iVoc (745 mV) and Joe (9.5 fA/cm2) are predictive for 1-Ω cm 200-μm wafer.•Dit of 1 × 1010 cm−2 eV−1 & Dph of < 1 × 10−4 is needed for a high-efficiency device.•Tunnel current (>0.01 A/cm2) of Si/SiO2/n+-Si structure is needed for obtaining a high FF (>84%).•A TOPCon solar cell with predictive efficiency is possible with a well-designed manufacture.In this work, we used the numerical simulation method to study the tunnel oxide passivated carrier-selective contacts (TOPCon) structured solar cells, with the focus especially on the paths towards excellent surface passivation and low contact resistance. The presence of an ultra-thin silicon oxide (SiO2) with high quality (typically low interface-states density, Dit ≈ 1 × 1010 cm−2 eV−1 and low pinhole density, Dph < 1 × 10−4) suppresses the recombination of carriers at the rear surface. As a result, implied open circuit voltage (iVoc) could be promoted by a value of more than 30 mV comparing with the solar cell without oxide layer, which is the primary benefit originated from TOPCon structure. Corresponding, the iVoc and recombination current density (Joe) could reach ∼745 mV and ∼9.5 fA/cm2 (Δn = 5 × 1015 cm−3) for the 1-Ω cm and 200-μm n-type wafer covered with high-quality oxide and n+-Si layers. In addition to passivation, a well-designed SiO2/n+-Si backside structure is also critical for carrier collection. The tunneling current is susceptible to oxide thickness, i.e., a 0.2-nm increase in SiO2 thickness results in the decrease of the tunneling current by more than one magnitude under certain circumstance. Fortunately, raising the doping in n+-Si layer enhances the tunneling possibility of electron, which allows for a thicker oxide that is favorable to a stable mass production. The simulation suggests that to obtain a high fill factor (FF, >84%), a minimum forward-bias saturated tunneling current of about 0.01 A/cm2, more favorable of 0.1 A/cm2, is required for the Si/SiO2/n+-Si structure. Generally, our work offers an improved understanding of tunnel oxide, doping layer and their combined effects on TOPCon solar cells. Besides simulation, we also discuss the practical manufactures of how to control the above mentioned parameters, as well as the problems needed to be solved for further work.

Poor light extraction efficiency (LEE) has been one of the major challenges responsible for the low external quantum efficiency of AlGaN-based ultraviolet light emitting Diodes (UV-LEDs). In this study, AlGaN nanostructure arrays were fabricated using a large-scale nanosphere self-assembly technique followed by reactive ion etching, and the transmission property of the AlGaN thin film and the photoluminescence (PL) behavior of AlGaN/GaN multiple-quantum-wells (MQWs) were investigated. A 90% light transmission value was obtained for the AlGaN thin film and a 2.5-fold increase in the band edge luminescence of the MQWs were obtained with an optimized nanostructure periodicity. Essentially, a general rule of periodicity-MQW emission wavelength matching criteria-was provided. Both the light transmission properties of the Al0.55Ga0.45N/AlN/sapphire thin film and the photoluminescence (PL) behavior of the AlGaN/GaN MQWs contribute to an improved understanding of the light extraction mechanism of PhC patterned UV-LEDs. Raman spectra also demonstrated the strain relaxation inside the MQW after nanostructure fabrication and thermal annealing. This study provides a pathway towards higher efficiency UV-LEDs with the help of a periodicity-wavelength matched nanostructure array.

Heterojunction solar cells (HSCs) featuring half and full contact of poly(3,4-ethylenedioxythiophene):polystyrene (PEDOT:PSS) with pyramid-textured silicon (Si) were thoroughly compared via simulations and experiments, and the following conclusions have been reached: (1) The insufficient electrical passivation inherent to the half contact results in enormous decline in short-circuit current density (Jsc) and open-circuit voltage (Voc). (2) For the full-contact HSCs, Jsc is mainly dependent on the recombination at the rear interface. With tuning of the contact properties from both sides, calculated (experimental) efficiencies of 14.46%/16.89% (13.94%/16.21%) for the half-/full-contact HSCs were finally obtained. A superior power conversion efficiency (PCE) over 21% is further predicted by considering more optimal contact resistance as well as doping concentration of Si. Our findings clarify why textured-Si/PEDOT:PSS HSCs show Voc and PCE that are inferior to those of planar counterparts in previous reports and further suggest a pathway to fully explore the efficiency potential of Si/PEDOT:PSS hybrid solar cells.

Recently, Si/organic polymer hybrid solar cells have been widely studied as the candidate for low-cost photovoltaics due to the simple low-temperature fabrication process. However, the rear electrode typically formed by directly depositing Al on the n-type Si is a Schottky contact, severely impacting the electron collecting efficiency. Here, an alcohol soluble polymer, poly[(9,9-bis(3′-(N,N-diethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), is firstly introduced to the Al/n-Si interface to improve the contact property, resulting in a remarkable reduced work function of the Al electrode and thus a good ohmic contact. An excellent photovoltaic efficiency of 13.35% is achieved in a planar device with a PFN layer. The facilitated electron collection efficiency associated with the ohmic contact not only improves the fill factor, but also enhances the short circuit current. Furthermore, the open circuit voltage increases significantly mainly due to the constructive effect of the built-in electric field of the rear contact on the total built-in electric field of the solar cell. Dark current–voltage, capacitance–voltage and electrochemical impedance spectra are used to systemically investigate the influence of the PFN layer on the performance, with prospects of receiving a high efficiency device with the quality rear contact.

Silicon/organic heterojunction solar cells (HSCs) based on conjugated polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and n-type silicon (n-Si) have attracted wide attention due to their potential advantages of high efficiency and low cost. However, the state-of-the-art efficiencies are still far from satisfactory due to the inferior junction quality. Here, facile treatments were applied by pretreating the n-Si wafer in tetramethylammonium hydroxide (TMAH) solution and using a capping copper iodide (CuI) layer on the PEDOT:PSS layer to achieve a high-quality Schottky junction. Detailed photoelectric characteristics indicated that the surface recombination was greatly suppressed after TMAH pretreatment, which increased the thickness of the interfacial oxide layer. Furthermore, the CuI capping layer induced a strong inversion layer near the n-Si surface, resulting in an excellent field effect passivation. With the collaborative improvements in the interface chemical and electrical passivation, a competitive open-circuit voltage of 0.656 V and a high fill factor of 78.1% were achieved, leading to a stable efficiency of over 14.3% for the planar n-Si/PEDOT:PSS HSCs. Our findings suggest promising strategies to further exploit the full voltage as well as efficiency potentials for Si/organic solar cells.Keywords: CuI; hybrid solar cells; inversion layer; Si/PEDOT:PSS; surface passivation; TMAH;

A high throughput surface texturing process for optical and optoelectric devices based on a large-area self-assembly of nanospheres via a low-cost micropropulsive injection (MPI) method is presented. The novel MPI process enables the formation of a well-organized monolayer of hexagonally arranged nanosphere arrays (NAs) with tunable periodicity directly on the water surface, which is then transferred onto the preset substrates. This process can readily reach a throughput of 3000 wafers/h, which is compatible with the high volume photovoltaic manufacturing, thereby presenting a highly versatile platform for the fabrication of periodic nanotexturing on device surfaces. Specifically, a double-sided grating texturing with top-sided nanopencils and bottom-sided inverted-nanopyramids is realized in a thin film of crystalline silicon (28 μm in thickness) using chemical etching on the mask of NAs to significantly enhance antireflection and light trapping, resulting in absorptions nearly approaching the Lambertian limit over a broad wavelength range of 375–1000 nm and even surpassing this limit beyond 1000 nm. In addition, it is demonstrated that the NAs can serve as templates for replicas of three-dimensional conformal amorphous silicon films with significantly enhanced light harvesting. The MPI induced self-assembly process may provide a universal and cost-effective solution for boosting light utilization, a problem of crucial importance for ultrathin solar cells.

Hybrid silicon/polymer solar cells promise to be an economically feasible alternative energy solution for various applications if ultrathin flexible crystalline silicon (c-Si) substrates are used. However, utilization of ultrathin c-Si encounters problems in light harvesting and electronic losses at surfaces, which severely degrade the performance of solar cells. Here, we developed a metal-assisted chemical etching method to deliver front-side surface texturing of hierarchically bowl-like nanopores on 20 μm c-Si, enabling an omnidirectional light harvesting over the entire solar spectrum as well as an enlarged contact area with the polymer. In addition, a back surface field was introduced on the back side of the thin c-Si to minimize the series resistance losses as well as to suppress the surface recombination by the built high–low junction. Through these improvements, a power conversion efficiency (PCE) up to 13.6% was achieved under an air mass 1.5 G irradiation for silicon/organic hybrid solar cells with the c-Si thickness of only about 20 μm. This PCE is as high as the record currently reported in hybrid solar cells constructed from bulk c-Si, suggesting a design rule for efficient silicon/organic solar cells with thinner absorbers.Keywords: charge recombination; heterojunction; hybrid solar cell; light trapping; surface nanotexturing;

Interfacial properties currently hinder the performance of Si/organic heterojunction solar cells for an alternative to high-efficiency and low-cost photovoltaics. Here, we present a simple and repeatable wet oxidation method for developing the surface passivation layer, SiOx, on the Si surface for the fabrication of high-efficiency Si/poly(3,4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT:PSS) heterojunction solar cells. The uniform and dense SiOx thin layer introduced by the oxidizing aqueous solution of H2O2 or HNO3 provided the better surface passivation and stronger wettability of the Si surface, compared to those in the native oxide case. These two types of progress helped create a lower defect density at the Si/PEDOT:PSS interface and thus a high-quality p–n junction with a lower interface recombination velocity. As a result, the HNO3-oxidized device displayed better performance with a power conversion efficiency (PCE) of 11%, representing a 28.96% enhancement from the PCE of 8.53% in the native oxide case. The effects on the performance of the Si/PEDOT:PSS hybrid solar cells of the wet oxidation treatment procedure, including the differences in surface roughness and wettability of the Si substrate, the quality and thickness of the SiOx, etc., were explored extensively. Such a simple and controllable oxidizing treatment could be an effective way to promote the interfacial properties that are an important cornerstone for more efficient Si/organic hybrid solar cells.Keywords: heterojunction solar cells; interface modification; Si/PEDOT:PSS; SiOx passivation; wet oxidation

Monodisperse anatase hierarchical microspheres were produced via a simple sol–gel process. These microspheres in the sub-wavelength diameter of 320–750 nm could scatter visible light efficiently as whispering gallery modes (WGM) corresponding to the dye sensitized wavelength, and load a large number of dye molecules with a large surface area (149.82 m2 g−1). Dye-sensitized solar cells (DSCs) based on the microsphere monolayer adsorbed light fully over the entire wavelength region and facilitated electrolyte diffusion due to larger voids between the microspheres, compared to the conventional film. Furthermore, the dynamics of electron transport and recombination was investigated systematically, indicating the higher charge collection efficiency of the TiO2 microsphere film. Overall, DSCs based on the 7.5 μm hierarchical microsphere monolayer exhibited more outstanding photovoltaic performances, yielding a high power conversion efficiency (PCE) of 11.43% under simulated AM 1.5 sunlight. Half of the normal film thickness was used to cut the device cost significantly.