Perovskite Solar Cells in the Shadow: Understanding the Mechanism of Reverse‐Bias Behavior toward Suppressed Reverse‐Bias Breakdown and Reverse‐Bias Induced Degradation

Abstract

to be connected in series to output larger voltage. Like any classical solar cell, when PSCs are connected in series for largearea modules and panels applications, special attention should be paid to the reverse bias electrical stress of the subcells, because excessive reverse bias due to shading effect (Figure 1a,b) is detrimental to the whole module. In the real environment, external factors such as trees, vegetation, dead leaves, wildlife, snow, and dark clouds will shade some units of the modules from the sun light, leading to the shading effect. For PSCs in modules, the shaded cells can be under reverse bias supplied by the other solar light irradiated cells, [2] as the photocurrent of the illuminated cells can flow to the shaded cells as a reverse current (Figure 1c,d), resulting in power dissipation and subcells thermal degradation that deteriorates the power output of the whole panel. [4][5][6] Joule heat generated in this process will even lead to the local irreversible thermal breakdown of the subcells in the shadow. [7][8][9] At present, however, the reverse bias stability issues of PSCs have not been systematically studied yet. Thus, investigating the phenomenon and mechanism of reverse bias behavior of PSCs, as well as the mechanism of reverse bias breakdown, with anticipating to improve the reverse stability of PSCs, is urgently necessary to promote the commercial application of PSCs.Generally, the overall performance of a solar module and panel depends on the beneficial performance of each individual subcell. Four essential parameters measuring the photovoltaic performance of a solar cell are PCE, FF, V oc , and J sc . In actual testing, these parameters are obtained under forward bias scan, which leads to more attention focusing on the forward bias portion of J-V curve than the reverse bias region. It is worth noting that the investigation of the reverse bias region of J-V curve is equally important, as the p-n junction characteristics of the PSCs is also reflected in their reverse bias behavior. [13][14][15][16][17][18] It has been reported that the reverse current density of classical solar cells (such as Si and CIGS) starts to increase abruptly when the reverse bias voltage is large In recent years, the power conversion efficiencies of halide perovskite solar cells (PSCs) have reached 25.7%. Further commercialization puts forward higher requirements for the stability of PSCs under different stresses. Current research on the stability of PSCs predominantly focuses on investigating the effects of temperature, humidity, oxygen, ultraviolet light, and electrical bias stress, while stability under reverse bias has been poorly studied among the many factors. When large-area application of PSCs panels occurs, the shading effect and local hot spots of PSCs modules in real scenarios all indicate that the research on reverse bias stability of PSCs is urgently needed. Within this review, a bird's-eye view of the recent advances on the reverse bias stability issue and reverse bias behavior of PSCs is obtai...

Multifunctional dual-interface layer enables efficient and stable inverted perovskite solar cells

“…It can be seen that optimizing the device structure helps to improve the reverse bias stability of the device, which is very helpful for future commercial components to cope with shading effects. 46,47 The improvement of the device bias stability may be due to the inhibition of ion migration by the interface layer. 48,49 Also, we tracked the normalization efficiency of three unencapsulated devices under dark conditions.…”

Physically and Chemically Stable Molybdenum‐Based Composite Electrodes for p–i–n Perovskite Solar Cells

“…Considering the practical application scenarios of the solar module, the shading effect tended to cause reverse bias in the sub-cells connected in series within the module. [37][38][39][40] As shown in Figure S20 (Supporting Information), the PCE for the Mo and Ag electrode device was monitored after being under a continuous 60 s duration of different bias voltages ranging from 1 to 5 V. The voltage applied on the metal electrode side was positive during the test. The Ag electrode device experienced complete failure after applying the 5 V bias, whereas the Mo electrode device was still able to maintain 87.4% of the initial efficiency.…”

Abnormal Dynamic Reverse Bias Behavior and Variable Reverse Breakdown Voltage of ETL‐free Perovskite Solar Cells

“…When the PV modules are working outdoors, some cells are likely to be shaded by snow, tree shade, bird droppings, and black clouds, etc. [ 15 ] Next, the shaded cells no longer act as a power output unit, but become a power dissipation diode. The illuminated cells continue to generate current, which forces the shaded cells into being under reverse bias.…”

“…[ 5 ] Until now, these limited reports indicate that the research on reverse bias behavior is far from enough in the field of PSCs, and its urgently needed to accelerate the establishment of standard procedures to judge the reverse bias stability of commercial PSCs. [ 7,15,26 ] In addition, there is potential for further optimization of the bias stability testing procedure (ISOS‐V) recommended in ref. [4].…”