The tunnel oxide passivated contact (TOPCon) structure got more consideration for development of high performance solar cells by the introduction of a tunnel oxide layer between the substrate and poly-Si is best for attaining interface passivation. The quality of passivation of the tunnel oxide layer clearly depends on the bond of SiO in the tunnel oxide layer, which is affected by the subsequent annealing and the tunnel oxide layer was formed in the suboxide region (SiO, Si₂O, Si₂O₃) at the interface with the substrate. In the suboxide region, an oxygen-rich bond is formed as a result of subsequent annealing that also improves the quality of passivation. To control the surface morphology, annealing profile, and acceleration rate, an oxide tunnel junction structure with a passivation characteristic of 700 mV or more (V_oc) on a p-type wafer could achieved. The quality of passivation of samples subjected to RTP annealing at temperatures above 900℃ declined rapidly. To improve the quality of passivation of the tunnel oxide layer, the physical properties and thermal stability of the thin layer must be considered. TOPCon silicon solar cell has a boron diffused front emitter, a tunnel-SiO_x/n⁺-poly-Si/SiN_x:H structure at the rear side, and screen-printed electrodes on both sides. The saturation currents J_o of this structure on polished surface is 1.3 fA/cm² and for textured silicon surfaces is 3.7 fA/cm² before printing the silver contacts. After printing the Ag contacts, the J_o of this structure increases to 50.7 fA/cm² on textured silicon surfaces, which is still manageably less for metal contacts. This structure was applied to TOPCon solar cells, resulting in a median efficiency of 23.91%, and a highest efficiency of 24.58%, independently. The conversion efficiency of interdigitated back-contact solar cells has reached up to 26% by enhancing the optoelectrical properties for both-sides-contacted of the cells.

The power conversion efficiency of Cu₂ZnSnSe₄ (CZTSe) solar cells depends on the absorber layer thickness; however, changes in the characteristics of the cells with varying absorber layer thickness are unclear. In this study, we investigated the changes in the characteristics of CZTSe solar cells for varying absorber layer thickness. Five absorber thicknesses were employed: CZTSe1 2.78 ㎛, CZTSe2 1.01 ㎛, CZTSe3 0.55 ㎛, CZTSe4 0.29 ㎛, and CZTSe5 0.15-0.23 ㎛. The efficiency of the CZTSe solar cells decreased as the absorber thickness decreased, resulting in power conversion efficiencies of 10.45% (CZTSe1), 8.67% (CZTSe2), 7.14% (CZTSe3), 3.44% (CZTSe4), and 1.54% (CZTSe5). As the thickness of the CZTSe absorber layer decreased, the electron-hole recombination at the grain boundaries and the absorber-back-contact interface increased. This caused an increase in the current loss, owing to light loss in the long-wavelength region. In addition, as the thickness of the CZTSe absorber layer decreased, more ZnSe was produced, and the resulting defects and defect clusters led to an open-circuit voltage loss.

Even though above 22% efficiencies have been reported in Cd-free Cu(In,Ga)Se₂ (CIGS) solar cell with Zn-containing buffers, the efficiencies with Zn-containing buffers, in general, are well below 20%. One of the reasons is Zn diffusion from the Zn-containing buffer layer to CIGS film during buffer growth. To avoid the degradation, it is necessary to prevent the diffusion of Zn atoms from Zn-containing buffer to CIGS film. For the purpose, we characterized an In₂Se₃ film as a possible diffusion barrier layer because In₂Se₃ has no Zn component. It was found that an In₂Se₃ layer grown at 300℃ was very effective in preventing Zn diffusion from a Zn-containing buffer. Also, the In₂Se₃ had a large potential barrier in the valence band at the In₂Se₃/CIGS interface. Therefore, In₂Se₃ passivation has the potential to achieve a super-high efficiency in CIGS solar cells that employ Cd-free ALD processed buffers containing Zn.

In order to perform photovoltaic (PV) operation and management (O&M) efficiently, individual PV module monitoring is becoming more important. In this research, we developed wireless IoT sensor which can monitor individual photovoltaic modules. This IoT sensor can detect the output voltage, current and module temperature of individual modules and provide monitored data by wireless communication. Measured voltage error was 1.23%, and it shows 16.6 dBM, 0.42sec and 7.1 mA for voltage, transmittance output, response time and mean power consumption, respectively. IoT sensors were demonstrated in the test field with real climate environment condition and each of 5 sensors showed precise results of voltage, current and temperature. Also, sensors were compared with commercial power-optimizers and showed result difference within 5%.